Skip to content
Snippets Groups Projects
Select Git revision
  • c2a9737f45e27d8263ff9643f994bda9bac0b944
  • kernelci-staging
  • linux-6.3-kselftest-build-fixes
  • linux-6.2-kselftest-build-fixes
  • linux-5.19-kselftest-llvm-x86-fix
  • linux-5.19-kselftest-lib-mk-error
  • linux-5.19-rc2-kselftest-build-fixup
  • linux-5.19-rc1-test-link
  • release-R94-14150.B-chromeos-4.14-serial
  • linux-5.15.rc6-vivid-no-fb
  • v5.15-mt8173-elm-hana-networking
  • linux-5.15-rc2-hana-mm-not-probed
  • for-kernelci
  • linux-5.14-rc3-vivid-no-fb
  • linux-5.14-rc3-hana-mm-not-probed
  • veyron-jaq-bisect
  • next-20210426-nyan-big-drm-read
  • next-20210419-nyan-big-drm-read
  • next-20210422-nyan-big-drm-read
  • next-20210416-nyan-big-drm-read
  • v5.11-vim3l-vhe
  • kernelci-bisect-snapshot-029
  • kernelci-bisect-snapshot-028
  • kernelci-staging-20230306.0
  • kernelci-staging-20230302.0
  • kernelci-staging-20230201.0
  • kernelci-bisect-snapshot-026
  • kernelci-bisect-snapshot-025
  • v5.15.68
  • next-20210422
  • next-20210419
  • next-20210416
  • next-20210222
  • v5.11
  • v5.11-rc6
  • v5.10-rc3
  • v5.10-rc2
  • kernelci-local-snapshot-064
  • kernelci-local-snapshot-063
  • v5.8-rc7
  • v5.7
41 results

filemap.c

Blame
  • filemap.c 77.47 KiB
    /*
     *	linux/mm/filemap.c
     *
     * Copyright (C) 1994-1999  Linus Torvalds
     */
    
    /*
     * This file handles the generic file mmap semantics used by
     * most "normal" filesystems (but you don't /have/ to use this:
     * the NFS filesystem used to do this differently, for example)
     */
    #include <linux/export.h>
    #include <linux/compiler.h>
    #include <linux/dax.h>
    #include <linux/fs.h>
    #include <linux/uaccess.h>
    #include <linux/capability.h>
    #include <linux/kernel_stat.h>
    #include <linux/gfp.h>
    #include <linux/mm.h>
    #include <linux/swap.h>
    #include <linux/mman.h>
    #include <linux/pagemap.h>
    #include <linux/file.h>
    #include <linux/uio.h>
    #include <linux/hash.h>
    #include <linux/writeback.h>
    #include <linux/backing-dev.h>
    #include <linux/pagevec.h>
    #include <linux/blkdev.h>
    #include <linux/security.h>
    #include <linux/cpuset.h>
    #include <linux/hardirq.h> /* for BUG_ON(!in_atomic()) only */
    #include <linux/hugetlb.h>
    #include <linux/memcontrol.h>
    #include <linux/cleancache.h>
    #include <linux/rmap.h>
    #include "internal.h"
    
    #define CREATE_TRACE_POINTS
    #include <trace/events/filemap.h>
    
    /*
     * FIXME: remove all knowledge of the buffer layer from the core VM
     */
    #include <linux/buffer_head.h> /* for try_to_free_buffers */
    
    #include <asm/mman.h>
    
    /*
     * Shared mappings implemented 30.11.1994. It's not fully working yet,
     * though.
     *
     * Shared mappings now work. 15.8.1995  Bruno.
     *
     * finished 'unifying' the page and buffer cache and SMP-threaded the
     * page-cache, 21.05.1999, Ingo Molnar <mingo@redhat.com>
     *
     * SMP-threaded pagemap-LRU 1999, Andrea Arcangeli <andrea@suse.de>
     */
    
    /*
     * Lock ordering:
     *
     *  ->i_mmap_rwsem		(truncate_pagecache)
     *    ->private_lock		(__free_pte->__set_page_dirty_buffers)
     *      ->swap_lock		(exclusive_swap_page, others)
     *        ->mapping->tree_lock
     *
     *  ->i_mutex
     *    ->i_mmap_rwsem		(truncate->unmap_mapping_range)
     *
     *  ->mmap_sem
     *    ->i_mmap_rwsem
     *      ->page_table_lock or pte_lock	(various, mainly in memory.c)
     *        ->mapping->tree_lock	(arch-dependent flush_dcache_mmap_lock)
     *
     *  ->mmap_sem
     *    ->lock_page		(access_process_vm)
     *
     *  ->i_mutex			(generic_perform_write)
     *    ->mmap_sem		(fault_in_pages_readable->do_page_fault)
     *
     *  bdi->wb.list_lock
     *    sb_lock			(fs/fs-writeback.c)
     *    ->mapping->tree_lock	(__sync_single_inode)
     *
     *  ->i_mmap_rwsem
     *    ->anon_vma.lock		(vma_adjust)
     *
     *  ->anon_vma.lock
     *    ->page_table_lock or pte_lock	(anon_vma_prepare and various)
     *
     *  ->page_table_lock or pte_lock
     *    ->swap_lock		(try_to_unmap_one)
     *    ->private_lock		(try_to_unmap_one)
     *    ->tree_lock		(try_to_unmap_one)
     *    ->zone_lru_lock(zone)	(follow_page->mark_page_accessed)
     *    ->zone_lru_lock(zone)	(check_pte_range->isolate_lru_page)
     *    ->private_lock		(page_remove_rmap->set_page_dirty)
     *    ->tree_lock		(page_remove_rmap->set_page_dirty)
     *    bdi.wb->list_lock		(page_remove_rmap->set_page_dirty)
     *    ->inode->i_lock		(page_remove_rmap->set_page_dirty)
     *    ->memcg->move_lock	(page_remove_rmap->lock_page_memcg)
     *    bdi.wb->list_lock		(zap_pte_range->set_page_dirty)
     *    ->inode->i_lock		(zap_pte_range->set_page_dirty)
     *    ->private_lock		(zap_pte_range->__set_page_dirty_buffers)
     *
     * ->i_mmap_rwsem
     *   ->tasklist_lock            (memory_failure, collect_procs_ao)
     */
    
    static int page_cache_tree_insert(struct address_space *mapping,
    				  struct page *page, void **shadowp)
    {
    	struct radix_tree_node *node;
    	void **slot;
    	int error;
    
    	error = __radix_tree_create(&mapping->page_tree, page->index, 0,
    				    &node, &slot);
    	if (error)
    		return error;
    	if (*slot) {
    		void *p;
    
    		p = radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
    		if (!radix_tree_exceptional_entry(p))
    			return -EEXIST;
    
    		mapping->nrexceptional--;
    		if (!dax_mapping(mapping)) {
    			if (shadowp)
    				*shadowp = p;
    			if (node)
    				workingset_node_shadows_dec(node);
    		} else {
    			/* DAX can replace empty locked entry with a hole */
    			WARN_ON_ONCE(p !=
    				(void *)(RADIX_TREE_EXCEPTIONAL_ENTRY |
    					 RADIX_DAX_ENTRY_LOCK));
    			/* DAX accounts exceptional entries as normal pages */
    			if (node)
    				workingset_node_pages_dec(node);
    			/* Wakeup waiters for exceptional entry lock */
    			dax_wake_mapping_entry_waiter(mapping, page->index,
    						      false);
    		}
    	}
    	radix_tree_replace_slot(slot, page);
    	mapping->nrpages++;
    	if (node) {
    		workingset_node_pages_inc(node);
    		/*
    		 * Don't track node that contains actual pages.
    		 *
    		 * Avoid acquiring the list_lru lock if already
    		 * untracked.  The list_empty() test is safe as
    		 * node->private_list is protected by
    		 * mapping->tree_lock.
    		 */
    		if (!list_empty(&node->private_list))
    			list_lru_del(&workingset_shadow_nodes,
    				     &node->private_list);
    	}
    	return 0;
    }
    
    static void page_cache_tree_delete(struct address_space *mapping,
    				   struct page *page, void *shadow)
    {
    	int i, nr = PageHuge(page) ? 1 : hpage_nr_pages(page);
    
    	VM_BUG_ON_PAGE(!PageLocked(page), page);
    	VM_BUG_ON_PAGE(PageTail(page), page);
    	VM_BUG_ON_PAGE(nr != 1 && shadow, page);
    
    	for (i = 0; i < nr; i++) {
    		struct radix_tree_node *node;
    		void **slot;
    
    		__radix_tree_lookup(&mapping->page_tree, page->index + i,
    				    &node, &slot);
    
    		radix_tree_clear_tags(&mapping->page_tree, node, slot);
    
    		if (!node) {
    			VM_BUG_ON_PAGE(nr != 1, page);
    			/*
    			 * We need a node to properly account shadow
    			 * entries. Don't plant any without. XXX
    			 */
    			shadow = NULL;
    		}
    
    		radix_tree_replace_slot(slot, shadow);
    
    		if (!node)
    			break;
    
    		workingset_node_pages_dec(node);
    		if (shadow)
    			workingset_node_shadows_inc(node);
    		else
    			if (__radix_tree_delete_node(&mapping->page_tree, node))
    				continue;
    
    		/*
    		 * Track node that only contains shadow entries. DAX mappings
    		 * contain no shadow entries and may contain other exceptional
    		 * entries so skip those.
    		 *
    		 * Avoid acquiring the list_lru lock if already tracked.
    		 * The list_empty() test is safe as node->private_list is
    		 * protected by mapping->tree_lock.
    		 */
    		if (!dax_mapping(mapping) && !workingset_node_pages(node) &&
    				list_empty(&node->private_list)) {
    			node->private_data = mapping;
    			list_lru_add(&workingset_shadow_nodes,
    					&node->private_list);
    		}
    	}
    
    	if (shadow) {
    		mapping->nrexceptional += nr;
    		/*
    		 * Make sure the nrexceptional update is committed before
    		 * the nrpages update so that final truncate racing
    		 * with reclaim does not see both counters 0 at the
    		 * same time and miss a shadow entry.
    		 */
    		smp_wmb();
    	}
    	mapping->nrpages -= nr;
    }
    
    /*
     * Delete a page from the page cache and free it. Caller has to make
     * sure the page is locked and that nobody else uses it - or that usage
     * is safe.  The caller must hold the mapping's tree_lock.
     */
    void __delete_from_page_cache(struct page *page, void *shadow)
    {
    	struct address_space *mapping = page->mapping;
    	int nr = hpage_nr_pages(page);
    
    	trace_mm_filemap_delete_from_page_cache(page);
    	/*
    	 * if we're uptodate, flush out into the cleancache, otherwise
    	 * invalidate any existing cleancache entries.  We can't leave
    	 * stale data around in the cleancache once our page is gone
    	 */
    	if (PageUptodate(page) && PageMappedToDisk(page))
    		cleancache_put_page(page);
    	else
    		cleancache_invalidate_page(mapping, page);
    
    	VM_BUG_ON_PAGE(PageTail(page), page);
    	VM_BUG_ON_PAGE(page_mapped(page), page);
    	if (!IS_ENABLED(CONFIG_DEBUG_VM) && unlikely(page_mapped(page))) {
    		int mapcount;
    
    		pr_alert("BUG: Bad page cache in process %s  pfn:%05lx\n",
    			 current->comm, page_to_pfn(page));
    		dump_page(page, "still mapped when deleted");
    		dump_stack();
    		add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
    
    		mapcount = page_mapcount(page);
    		if (mapping_exiting(mapping) &&
    		    page_count(page) >= mapcount + 2) {
    			/*
    			 * All vmas have already been torn down, so it's
    			 * a good bet that actually the page is unmapped,
    			 * and we'd prefer not to leak it: if we're wrong,
    			 * some other bad page check should catch it later.
    			 */
    			page_mapcount_reset(page);
    			page_ref_sub(page, mapcount);
    		}
    	}
    
    	page_cache_tree_delete(mapping, page, shadow);
    
    	page->mapping = NULL;
    	/* Leave page->index set: truncation lookup relies upon it */
    
    	/* hugetlb pages do not participate in page cache accounting. */
    	if (!PageHuge(page))
    		__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, -nr);
    	if (PageSwapBacked(page)) {
    		__mod_node_page_state(page_pgdat(page), NR_SHMEM, -nr);
    		if (PageTransHuge(page))
    			__dec_node_page_state(page, NR_SHMEM_THPS);
    	} else {
    		VM_BUG_ON_PAGE(PageTransHuge(page) && !PageHuge(page), page);
    	}
    
    	/*
    	 * At this point page must be either written or cleaned by truncate.
    	 * Dirty page here signals a bug and loss of unwritten data.
    	 *
    	 * This fixes dirty accounting after removing the page entirely but
    	 * leaves PageDirty set: it has no effect for truncated page and
    	 * anyway will be cleared before returning page into buddy allocator.
    	 */
    	if (WARN_ON_ONCE(PageDirty(page)))
    		account_page_cleaned(page, mapping, inode_to_wb(mapping->host));
    }
    
    /**
     * delete_from_page_cache - delete page from page cache
     * @page: the page which the kernel is trying to remove from page cache
     *
     * This must be called only on pages that have been verified to be in the page
     * cache and locked.  It will never put the page into the free list, the caller
     * has a reference on the page.
     */
    void delete_from_page_cache(struct page *page)
    {
    	struct address_space *mapping = page_mapping(page);
    	unsigned long flags;
    	void (*freepage)(struct page *);
    
    	BUG_ON(!PageLocked(page));
    
    	freepage = mapping->a_ops->freepage;
    
    	spin_lock_irqsave(&mapping->tree_lock, flags);
    	__delete_from_page_cache(page, NULL);
    	spin_unlock_irqrestore(&mapping->tree_lock, flags);
    
    	if (freepage)
    		freepage(page);
    
    	if (PageTransHuge(page) && !PageHuge(page)) {
    		page_ref_sub(page, HPAGE_PMD_NR);
    		VM_BUG_ON_PAGE(page_count(page) <= 0, page);
    	} else {
    		put_page(page);
    	}
    }
    EXPORT_SYMBOL(delete_from_page_cache);
    
    int filemap_check_errors(struct address_space *mapping)
    {
    	int ret = 0;
    	/* Check for outstanding write errors */
    	if (test_bit(AS_ENOSPC, &mapping->flags) &&
    	    test_and_clear_bit(AS_ENOSPC, &mapping->flags))
    		ret = -ENOSPC;
    	if (test_bit(AS_EIO, &mapping->flags) &&
    	    test_and_clear_bit(AS_EIO, &mapping->flags))
    		ret = -EIO;
    	return ret;
    }
    EXPORT_SYMBOL(filemap_check_errors);
    
    /**
     * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
     * @mapping:	address space structure to write
     * @start:	offset in bytes where the range starts
     * @end:	offset in bytes where the range ends (inclusive)
     * @sync_mode:	enable synchronous operation
     *
     * Start writeback against all of a mapping's dirty pages that lie
     * within the byte offsets <start, end> inclusive.
     *
     * If sync_mode is WB_SYNC_ALL then this is a "data integrity" operation, as
     * opposed to a regular memory cleansing writeback.  The difference between
     * these two operations is that if a dirty page/buffer is encountered, it must
     * be waited upon, and not just skipped over.
     */
    int __filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
    				loff_t end, int sync_mode)
    {
    	int ret;
    	struct writeback_control wbc = {
    		.sync_mode = sync_mode,
    		.nr_to_write = LONG_MAX,
    		.range_start = start,
    		.range_end = end,
    	};
    
    	if (!mapping_cap_writeback_dirty(mapping))
    		return 0;
    
    	wbc_attach_fdatawrite_inode(&wbc, mapping->host);
    	ret = do_writepages(mapping, &wbc);
    	wbc_detach_inode(&wbc);
    	return ret;
    }
    
    static inline int __filemap_fdatawrite(struct address_space *mapping,
    	int sync_mode)
    {
    	return __filemap_fdatawrite_range(mapping, 0, LLONG_MAX, sync_mode);
    }
    
    int filemap_fdatawrite(struct address_space *mapping)
    {
    	return __filemap_fdatawrite(mapping, WB_SYNC_ALL);
    }
    EXPORT_SYMBOL(filemap_fdatawrite);
    
    int filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
    				loff_t end)
    {
    	return __filemap_fdatawrite_range(mapping, start, end, WB_SYNC_ALL);
    }
    EXPORT_SYMBOL(filemap_fdatawrite_range);
    
    /**
     * filemap_flush - mostly a non-blocking flush
     * @mapping:	target address_space
     *
     * This is a mostly non-blocking flush.  Not suitable for data-integrity
     * purposes - I/O may not be started against all dirty pages.
     */
    int filemap_flush(struct address_space *mapping)
    {
    	return __filemap_fdatawrite(mapping, WB_SYNC_NONE);
    }
    EXPORT_SYMBOL(filemap_flush);
    
    static int __filemap_fdatawait_range(struct address_space *mapping,
    				     loff_t start_byte, loff_t end_byte)
    {
    	pgoff_t index = start_byte >> PAGE_SHIFT;
    	pgoff_t end = end_byte >> PAGE_SHIFT;
    	struct pagevec pvec;
    	int nr_pages;
    	int ret = 0;
    
    	if (end_byte < start_byte)
    		goto out;
    
    	pagevec_init(&pvec, 0);
    	while ((index <= end) &&
    			(nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
    			PAGECACHE_TAG_WRITEBACK,
    			min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1)) != 0) {
    		unsigned i;
    
    		for (i = 0; i < nr_pages; i++) {
    			struct page *page = pvec.pages[i];
    
    			/* until radix tree lookup accepts end_index */
    			if (page->index > end)
    				continue;
    
    			wait_on_page_writeback(page);
    			if (TestClearPageError(page))
    				ret = -EIO;
    		}
    		pagevec_release(&pvec);
    		cond_resched();
    	}
    out:
    	return ret;
    }
    
    /**
     * filemap_fdatawait_range - wait for writeback to complete
     * @mapping:		address space structure to wait for
     * @start_byte:		offset in bytes where the range starts
     * @end_byte:		offset in bytes where the range ends (inclusive)
     *
     * Walk the list of under-writeback pages of the given address space
     * in the given range and wait for all of them.  Check error status of
     * the address space and return it.
     *
     * Since the error status of the address space is cleared by this function,
     * callers are responsible for checking the return value and handling and/or
     * reporting the error.
     */
    int filemap_fdatawait_range(struct address_space *mapping, loff_t start_byte,
    			    loff_t end_byte)
    {
    	int ret, ret2;
    
    	ret = __filemap_fdatawait_range(mapping, start_byte, end_byte);
    	ret2 = filemap_check_errors(mapping);
    	if (!ret)
    		ret = ret2;
    
    	return ret;
    }
    EXPORT_SYMBOL(filemap_fdatawait_range);
    
    /**
     * filemap_fdatawait_keep_errors - wait for writeback without clearing errors
     * @mapping: address space structure to wait for
     *
     * Walk the list of under-writeback pages of the given address space
     * and wait for all of them.  Unlike filemap_fdatawait(), this function
     * does not clear error status of the address space.
     *
     * Use this function if callers don't handle errors themselves.  Expected
     * call sites are system-wide / filesystem-wide data flushers: e.g. sync(2),
     * fsfreeze(8)
     */
    void filemap_fdatawait_keep_errors(struct address_space *mapping)
    {
    	loff_t i_size = i_size_read(mapping->host);
    
    	if (i_size == 0)
    		return;
    
    	__filemap_fdatawait_range(mapping, 0, i_size - 1);
    }
    
    /**
     * filemap_fdatawait - wait for all under-writeback pages to complete
     * @mapping: address space structure to wait for
     *
     * Walk the list of under-writeback pages of the given address space
     * and wait for all of them.  Check error status of the address space
     * and return it.
     *
     * Since the error status of the address space is cleared by this function,
     * callers are responsible for checking the return value and handling and/or
     * reporting the error.
     */
    int filemap_fdatawait(struct address_space *mapping)
    {
    	loff_t i_size = i_size_read(mapping->host);
    
    	if (i_size == 0)
    		return 0;
    
    	return filemap_fdatawait_range(mapping, 0, i_size - 1);
    }
    EXPORT_SYMBOL(filemap_fdatawait);
    
    int filemap_write_and_wait(struct address_space *mapping)
    {
    	int err = 0;
    
    	if ((!dax_mapping(mapping) && mapping->nrpages) ||
    	    (dax_mapping(mapping) && mapping->nrexceptional)) {
    		err = filemap_fdatawrite(mapping);
    		/*
    		 * Even if the above returned error, the pages may be
    		 * written partially (e.g. -ENOSPC), so we wait for it.
    		 * But the -EIO is special case, it may indicate the worst
    		 * thing (e.g. bug) happened, so we avoid waiting for it.
    		 */
    		if (err != -EIO) {
    			int err2 = filemap_fdatawait(mapping);
    			if (!err)
    				err = err2;
    		}
    	} else {
    		err = filemap_check_errors(mapping);
    	}
    	return err;
    }
    EXPORT_SYMBOL(filemap_write_and_wait);
    
    /**
     * filemap_write_and_wait_range - write out & wait on a file range
     * @mapping:	the address_space for the pages
     * @lstart:	offset in bytes where the range starts
     * @lend:	offset in bytes where the range ends (inclusive)
     *
     * Write out and wait upon file offsets lstart->lend, inclusive.
     *
     * Note that `lend' is inclusive (describes the last byte to be written) so
     * that this function can be used to write to the very end-of-file (end = -1).
     */
    int filemap_write_and_wait_range(struct address_space *mapping,
    				 loff_t lstart, loff_t lend)
    {
    	int err = 0;
    
    	if ((!dax_mapping(mapping) && mapping->nrpages) ||
    	    (dax_mapping(mapping) && mapping->nrexceptional)) {
    		err = __filemap_fdatawrite_range(mapping, lstart, lend,
    						 WB_SYNC_ALL);
    		/* See comment of filemap_write_and_wait() */
    		if (err != -EIO) {
    			int err2 = filemap_fdatawait_range(mapping,
    						lstart, lend);
    			if (!err)
    				err = err2;
    		}
    	} else {
    		err = filemap_check_errors(mapping);
    	}
    	return err;
    }
    EXPORT_SYMBOL(filemap_write_and_wait_range);
    
    /**
     * replace_page_cache_page - replace a pagecache page with a new one
     * @old:	page to be replaced
     * @new:	page to replace with
     * @gfp_mask:	allocation mode
     *
     * This function replaces a page in the pagecache with a new one.  On
     * success it acquires the pagecache reference for the new page and
     * drops it for the old page.  Both the old and new pages must be
     * locked.  This function does not add the new page to the LRU, the
     * caller must do that.
     *
     * The remove + add is atomic.  The only way this function can fail is
     * memory allocation failure.
     */
    int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
    {
    	int error;
    
    	VM_BUG_ON_PAGE(!PageLocked(old), old);
    	VM_BUG_ON_PAGE(!PageLocked(new), new);
    	VM_BUG_ON_PAGE(new->mapping, new);
    
    	error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
    	if (!error) {
    		struct address_space *mapping = old->mapping;
    		void (*freepage)(struct page *);
    		unsigned long flags;
    
    		pgoff_t offset = old->index;
    		freepage = mapping->a_ops->freepage;
    
    		get_page(new);
    		new->mapping = mapping;
    		new->index = offset;
    
    		spin_lock_irqsave(&mapping->tree_lock, flags);
    		__delete_from_page_cache(old, NULL);
    		error = page_cache_tree_insert(mapping, new, NULL);
    		BUG_ON(error);
    
    		/*
    		 * hugetlb pages do not participate in page cache accounting.
    		 */
    		if (!PageHuge(new))
    			__inc_node_page_state(new, NR_FILE_PAGES);
    		if (PageSwapBacked(new))
    			__inc_node_page_state(new, NR_SHMEM);
    		spin_unlock_irqrestore(&mapping->tree_lock, flags);
    		mem_cgroup_migrate(old, new);
    		radix_tree_preload_end();
    		if (freepage)
    			freepage(old);
    		put_page(old);
    	}
    
    	return error;
    }
    EXPORT_SYMBOL_GPL(replace_page_cache_page);
    
    static int __add_to_page_cache_locked(struct page *page,
    				      struct address_space *mapping,
    				      pgoff_t offset, gfp_t gfp_mask,
    				      void **shadowp)
    {
    	int huge = PageHuge(page);
    	struct mem_cgroup *memcg;
    	int error;
    
    	VM_BUG_ON_PAGE(!PageLocked(page), page);
    	VM_BUG_ON_PAGE(PageSwapBacked(page), page);
    
    	if (!huge) {
    		error = mem_cgroup_try_charge(page, current->mm,
    					      gfp_mask, &memcg, false);
    		if (error)
    			return error;
    	}
    
    	error = radix_tree_maybe_preload(gfp_mask & ~__GFP_HIGHMEM);
    	if (error) {
    		if (!huge)
    			mem_cgroup_cancel_charge(page, memcg, false);
    		return error;
    	}
    
    	get_page(page);
    	page->mapping = mapping;
    	page->index = offset;
    
    	spin_lock_irq(&mapping->tree_lock);
    	error = page_cache_tree_insert(mapping, page, shadowp);
    	radix_tree_preload_end();
    	if (unlikely(error))
    		goto err_insert;
    
    	/* hugetlb pages do not participate in page cache accounting. */
    	if (!huge)
    		__inc_node_page_state(page, NR_FILE_PAGES);
    	spin_unlock_irq(&mapping->tree_lock);
    	if (!huge)
    		mem_cgroup_commit_charge(page, memcg, false, false);
    	trace_mm_filemap_add_to_page_cache(page);
    	return 0;
    err_insert:
    	page->mapping = NULL;
    	/* Leave page->index set: truncation relies upon it */
    	spin_unlock_irq(&mapping->tree_lock);
    	if (!huge)
    		mem_cgroup_cancel_charge(page, memcg, false);
    	put_page(page);
    	return error;
    }
    
    /**
     * add_to_page_cache_locked - add a locked page to the pagecache
     * @page:	page to add
     * @mapping:	the page's address_space
     * @offset:	page index
     * @gfp_mask:	page allocation mode
     *
     * This function is used to add a page to the pagecache. It must be locked.
     * This function does not add the page to the LRU.  The caller must do that.
     */
    int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
    		pgoff_t offset, gfp_t gfp_mask)
    {
    	return __add_to_page_cache_locked(page, mapping, offset,
    					  gfp_mask, NULL);
    }
    EXPORT_SYMBOL(add_to_page_cache_locked);
    
    int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
    				pgoff_t offset, gfp_t gfp_mask)
    {
    	void *shadow = NULL;
    	int ret;
    
    	__SetPageLocked(page);
    	ret = __add_to_page_cache_locked(page, mapping, offset,
    					 gfp_mask, &shadow);
    	if (unlikely(ret))
    		__ClearPageLocked(page);
    	else {
    		/*
    		 * The page might have been evicted from cache only
    		 * recently, in which case it should be activated like
    		 * any other repeatedly accessed page.
    		 * The exception is pages getting rewritten; evicting other
    		 * data from the working set, only to cache data that will
    		 * get overwritten with something else, is a waste of memory.
    		 */
    		if (!(gfp_mask & __GFP_WRITE) &&
    		    shadow && workingset_refault(shadow)) {
    			SetPageActive(page);
    			workingset_activation(page);
    		} else
    			ClearPageActive(page);
    		lru_cache_add(page);
    	}
    	return ret;
    }
    EXPORT_SYMBOL_GPL(add_to_page_cache_lru);
    
    #ifdef CONFIG_NUMA
    struct page *__page_cache_alloc(gfp_t gfp)
    {
    	int n;
    	struct page *page;
    
    	if (cpuset_do_page_mem_spread()) {
    		unsigned int cpuset_mems_cookie;
    		do {
    			cpuset_mems_cookie = read_mems_allowed_begin();
    			n = cpuset_mem_spread_node();
    			page = __alloc_pages_node(n, gfp, 0);
    		} while (!page && read_mems_allowed_retry(cpuset_mems_cookie));
    
    		return page;
    	}
    	return alloc_pages(gfp, 0);
    }
    EXPORT_SYMBOL(__page_cache_alloc);
    #endif
    
    /*
     * In order to wait for pages to become available there must be
     * waitqueues associated with pages. By using a hash table of
     * waitqueues where the bucket discipline is to maintain all
     * waiters on the same queue and wake all when any of the pages
     * become available, and for the woken contexts to check to be
     * sure the appropriate page became available, this saves space
     * at a cost of "thundering herd" phenomena during rare hash
     * collisions.
     */
    wait_queue_head_t *page_waitqueue(struct page *page)
    {
    	const struct zone *zone = page_zone(page);
    
    	return &zone->wait_table[hash_ptr(page, zone->wait_table_bits)];
    }
    EXPORT_SYMBOL(page_waitqueue);
    
    void wait_on_page_bit(struct page *page, int bit_nr)
    {
    	DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
    
    	if (test_bit(bit_nr, &page->flags))
    		__wait_on_bit(page_waitqueue(page), &wait, bit_wait_io,
    							TASK_UNINTERRUPTIBLE);
    }
    EXPORT_SYMBOL(wait_on_page_bit);
    
    int wait_on_page_bit_killable(struct page *page, int bit_nr)
    {
    	DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
    
    	if (!test_bit(bit_nr, &page->flags))
    		return 0;
    
    	return __wait_on_bit(page_waitqueue(page), &wait,
    			     bit_wait_io, TASK_KILLABLE);
    }
    
    int wait_on_page_bit_killable_timeout(struct page *page,
    				       int bit_nr, unsigned long timeout)
    {
    	DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
    
    	wait.key.timeout = jiffies + timeout;
    	if (!test_bit(bit_nr, &page->flags))
    		return 0;
    	return __wait_on_bit(page_waitqueue(page), &wait,
    			     bit_wait_io_timeout, TASK_KILLABLE);
    }
    EXPORT_SYMBOL_GPL(wait_on_page_bit_killable_timeout);
    
    /**
     * add_page_wait_queue - Add an arbitrary waiter to a page's wait queue
     * @page: Page defining the wait queue of interest
     * @waiter: Waiter to add to the queue
     *
     * Add an arbitrary @waiter to the wait queue for the nominated @page.
     */
    void add_page_wait_queue(struct page *page, wait_queue_t *waiter)
    {
    	wait_queue_head_t *q = page_waitqueue(page);
    	unsigned long flags;
    
    	spin_lock_irqsave(&q->lock, flags);
    	__add_wait_queue(q, waiter);
    	spin_unlock_irqrestore(&q->lock, flags);
    }
    EXPORT_SYMBOL_GPL(add_page_wait_queue);
    
    /**
     * unlock_page - unlock a locked page
     * @page: the page
     *
     * Unlocks the page and wakes up sleepers in ___wait_on_page_locked().
     * Also wakes sleepers in wait_on_page_writeback() because the wakeup
     * mechanism between PageLocked pages and PageWriteback pages is shared.
     * But that's OK - sleepers in wait_on_page_writeback() just go back to sleep.
     *
     * The mb is necessary to enforce ordering between the clear_bit and the read
     * of the waitqueue (to avoid SMP races with a parallel wait_on_page_locked()).
     */
    void unlock_page(struct page *page)
    {
    	page = compound_head(page);
    	VM_BUG_ON_PAGE(!PageLocked(page), page);
    	clear_bit_unlock(PG_locked, &page->flags);
    	smp_mb__after_atomic();
    	wake_up_page(page, PG_locked);
    }
    EXPORT_SYMBOL(unlock_page);
    
    /**
     * end_page_writeback - end writeback against a page
     * @page: the page
     */
    void end_page_writeback(struct page *page)
    {
    	/*
    	 * TestClearPageReclaim could be used here but it is an atomic
    	 * operation and overkill in this particular case. Failing to
    	 * shuffle a page marked for immediate reclaim is too mild to
    	 * justify taking an atomic operation penalty at the end of
    	 * ever page writeback.
    	 */
    	if (PageReclaim(page)) {
    		ClearPageReclaim(page);
    		rotate_reclaimable_page(page);
    	}
    
    	if (!test_clear_page_writeback(page))
    		BUG();
    
    	smp_mb__after_atomic();
    	wake_up_page(page, PG_writeback);
    }
    EXPORT_SYMBOL(end_page_writeback);
    
    /*
     * After completing I/O on a page, call this routine to update the page
     * flags appropriately
     */
    void page_endio(struct page *page, bool is_write, int err)
    {
    	if (!is_write) {
    		if (!err) {
    			SetPageUptodate(page);
    		} else {
    			ClearPageUptodate(page);
    			SetPageError(page);
    		}
    		unlock_page(page);
    	} else {
    		if (err) {
    			SetPageError(page);
    			if (page->mapping)
    				mapping_set_error(page->mapping, err);
    		}
    		end_page_writeback(page);
    	}
    }
    EXPORT_SYMBOL_GPL(page_endio);
    
    /**
     * __lock_page - get a lock on the page, assuming we need to sleep to get it
     * @page: the page to lock
     */
    void __lock_page(struct page *page)
    {
    	struct page *page_head = compound_head(page);
    	DEFINE_WAIT_BIT(wait, &page_head->flags, PG_locked);
    
    	__wait_on_bit_lock(page_waitqueue(page_head), &wait, bit_wait_io,
    							TASK_UNINTERRUPTIBLE);
    }
    EXPORT_SYMBOL(__lock_page);
    
    int __lock_page_killable(struct page *page)
    {
    	struct page *page_head = compound_head(page);
    	DEFINE_WAIT_BIT(wait, &page_head->flags, PG_locked);
    
    	return __wait_on_bit_lock(page_waitqueue(page_head), &wait,
    					bit_wait_io, TASK_KILLABLE);
    }
    EXPORT_SYMBOL_GPL(__lock_page_killable);
    
    /*
     * Return values:
     * 1 - page is locked; mmap_sem is still held.
     * 0 - page is not locked.
     *     mmap_sem has been released (up_read()), unless flags had both
     *     FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_RETRY_NOWAIT set, in
     *     which case mmap_sem is still held.
     *
     * If neither ALLOW_RETRY nor KILLABLE are set, will always return 1
     * with the page locked and the mmap_sem unperturbed.
     */
    int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
    			 unsigned int flags)
    {
    	if (flags & FAULT_FLAG_ALLOW_RETRY) {
    		/*
    		 * CAUTION! In this case, mmap_sem is not released
    		 * even though return 0.
    		 */
    		if (flags & FAULT_FLAG_RETRY_NOWAIT)
    			return 0;
    
    		up_read(&mm->mmap_sem);
    		if (flags & FAULT_FLAG_KILLABLE)
    			wait_on_page_locked_killable(page);
    		else
    			wait_on_page_locked(page);
    		return 0;
    	} else {
    		if (flags & FAULT_FLAG_KILLABLE) {
    			int ret;
    
    			ret = __lock_page_killable(page);
    			if (ret) {
    				up_read(&mm->mmap_sem);
    				return 0;
    			}
    		} else
    			__lock_page(page);
    		return 1;
    	}
    }
    
    /**
     * page_cache_next_hole - find the next hole (not-present entry)
     * @mapping: mapping
     * @index: index
     * @max_scan: maximum range to search
     *
     * Search the set [index, min(index+max_scan-1, MAX_INDEX)] for the
     * lowest indexed hole.
     *
     * Returns: the index of the hole if found, otherwise returns an index
     * outside of the set specified (in which case 'return - index >=
     * max_scan' will be true). In rare cases of index wrap-around, 0 will
     * be returned.
     *
     * page_cache_next_hole may be called under rcu_read_lock. However,
     * like radix_tree_gang_lookup, this will not atomically search a
     * snapshot of the tree at a single point in time. For example, if a
     * hole is created at index 5, then subsequently a hole is created at
     * index 10, page_cache_next_hole covering both indexes may return 10
     * if called under rcu_read_lock.
     */
    pgoff_t page_cache_next_hole(struct address_space *mapping,
    			     pgoff_t index, unsigned long max_scan)
    {
    	unsigned long i;
    
    	for (i = 0; i < max_scan; i++) {
    		struct page *page;
    
    		page = radix_tree_lookup(&mapping->page_tree, index);
    		if (!page || radix_tree_exceptional_entry(page))
    			break;
    		index++;
    		if (index == 0)
    			break;
    	}
    
    	return index;
    }
    EXPORT_SYMBOL(page_cache_next_hole);
    
    /**
     * page_cache_prev_hole - find the prev hole (not-present entry)
     * @mapping: mapping
     * @index: index
     * @max_scan: maximum range to search
     *
     * Search backwards in the range [max(index-max_scan+1, 0), index] for
     * the first hole.
     *
     * Returns: the index of the hole if found, otherwise returns an index
     * outside of the set specified (in which case 'index - return >=
     * max_scan' will be true). In rare cases of wrap-around, ULONG_MAX
     * will be returned.
     *
     * page_cache_prev_hole may be called under rcu_read_lock. However,
     * like radix_tree_gang_lookup, this will not atomically search a
     * snapshot of the tree at a single point in time. For example, if a
     * hole is created at index 10, then subsequently a hole is created at
     * index 5, page_cache_prev_hole covering both indexes may return 5 if
     * called under rcu_read_lock.
     */
    pgoff_t page_cache_prev_hole(struct address_space *mapping,
    			     pgoff_t index, unsigned long max_scan)
    {
    	unsigned long i;
    
    	for (i = 0; i < max_scan; i++) {
    		struct page *page;
    
    		page = radix_tree_lookup(&mapping->page_tree, index);
    		if (!page || radix_tree_exceptional_entry(page))
    			break;
    		index--;
    		if (index == ULONG_MAX)
    			break;
    	}
    
    	return index;
    }
    EXPORT_SYMBOL(page_cache_prev_hole);
    
    /**
     * find_get_entry - find and get a page cache entry
     * @mapping: the address_space to search
     * @offset: the page cache index
     *
     * Looks up the page cache slot at @mapping & @offset.  If there is a
     * page cache page, it is returned with an increased refcount.
     *
     * If the slot holds a shadow entry of a previously evicted page, or a
     * swap entry from shmem/tmpfs, it is returned.
     *
     * Otherwise, %NULL is returned.
     */
    struct page *find_get_entry(struct address_space *mapping, pgoff_t offset)
    {
    	void **pagep;
    	struct page *head, *page;
    
    	rcu_read_lock();
    repeat:
    	page = NULL;
    	pagep = radix_tree_lookup_slot(&mapping->page_tree, offset);
    	if (pagep) {
    		page = radix_tree_deref_slot(pagep);
    		if (unlikely(!page))
    			goto out;
    		if (radix_tree_exception(page)) {
    			if (radix_tree_deref_retry(page))
    				goto repeat;
    			/*
    			 * A shadow entry of a recently evicted page,
    			 * or a swap entry from shmem/tmpfs.  Return
    			 * it without attempting to raise page count.
    			 */
    			goto out;
    		}
    
    		head = compound_head(page);
    		if (!page_cache_get_speculative(head))
    			goto repeat;
    
    		/* The page was split under us? */
    		if (compound_head(page) != head) {
    			put_page(head);
    			goto repeat;
    		}
    
    		/*
    		 * Has the page moved?
    		 * This is part of the lockless pagecache protocol. See
    		 * include/linux/pagemap.h for details.
    		 */
    		if (unlikely(page != *pagep)) {
    			put_page(head);
    			goto repeat;
    		}
    	}
    out:
    	rcu_read_unlock();
    
    	return page;
    }
    EXPORT_SYMBOL(find_get_entry);
    
    /**
     * find_lock_entry - locate, pin and lock a page cache entry
     * @mapping: the address_space to search
     * @offset: the page cache index
     *
     * Looks up the page cache slot at @mapping & @offset.  If there is a
     * page cache page, it is returned locked and with an increased
     * refcount.
     *
     * If the slot holds a shadow entry of a previously evicted page, or a
     * swap entry from shmem/tmpfs, it is returned.
     *
     * Otherwise, %NULL is returned.
     *
     * find_lock_entry() may sleep.
     */
    struct page *find_lock_entry(struct address_space *mapping, pgoff_t offset)
    {
    	struct page *page;
    
    repeat:
    	page = find_get_entry(mapping, offset);
    	if (page && !radix_tree_exception(page)) {
    		lock_page(page);
    		/* Has the page been truncated? */
    		if (unlikely(page_mapping(page) != mapping)) {
    			unlock_page(page);
    			put_page(page);
    			goto repeat;
    		}
    		VM_BUG_ON_PAGE(page_to_pgoff(page) != offset, page);
    	}
    	return page;
    }
    EXPORT_SYMBOL(find_lock_entry);
    
    /**
     * pagecache_get_page - find and get a page reference
     * @mapping: the address_space to search
     * @offset: the page index
     * @fgp_flags: PCG flags
     * @gfp_mask: gfp mask to use for the page cache data page allocation
     *
     * Looks up the page cache slot at @mapping & @offset.
     *
     * PCG flags modify how the page is returned.
     *
     * FGP_ACCESSED: the page will be marked accessed
     * FGP_LOCK: Page is return locked
     * FGP_CREAT: If page is not present then a new page is allocated using
     *		@gfp_mask and added to the page cache and the VM's LRU
     *		list. The page is returned locked and with an increased
     *		refcount. Otherwise, %NULL is returned.
     *
     * If FGP_LOCK or FGP_CREAT are specified then the function may sleep even
     * if the GFP flags specified for FGP_CREAT are atomic.
     *
     * If there is a page cache page, it is returned with an increased refcount.
     */
    struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
    	int fgp_flags, gfp_t gfp_mask)
    {
    	struct page *page;
    
    repeat:
    	page = find_get_entry(mapping, offset);
    	if (radix_tree_exceptional_entry(page))
    		page = NULL;
    	if (!page)
    		goto no_page;
    
    	if (fgp_flags & FGP_LOCK) {
    		if (fgp_flags & FGP_NOWAIT) {
    			if (!trylock_page(page)) {
    				put_page(page);
    				return NULL;
    			}
    		} else {
    			lock_page(page);
    		}
    
    		/* Has the page been truncated? */
    		if (unlikely(page->mapping != mapping)) {
    			unlock_page(page);
    			put_page(page);
    			goto repeat;
    		}
    		VM_BUG_ON_PAGE(page->index != offset, page);
    	}
    
    	if (page && (fgp_flags & FGP_ACCESSED))
    		mark_page_accessed(page);
    
    no_page:
    	if (!page && (fgp_flags & FGP_CREAT)) {
    		int err;
    		if ((fgp_flags & FGP_WRITE) && mapping_cap_account_dirty(mapping))
    			gfp_mask |= __GFP_WRITE;
    		if (fgp_flags & FGP_NOFS)
    			gfp_mask &= ~__GFP_FS;
    
    		page = __page_cache_alloc(gfp_mask);
    		if (!page)
    			return NULL;
    
    		if (WARN_ON_ONCE(!(fgp_flags & FGP_LOCK)))
    			fgp_flags |= FGP_LOCK;
    
    		/* Init accessed so avoid atomic mark_page_accessed later */
    		if (fgp_flags & FGP_ACCESSED)
    			__SetPageReferenced(page);
    
    		err = add_to_page_cache_lru(page, mapping, offset,
    				gfp_mask & GFP_RECLAIM_MASK);
    		if (unlikely(err)) {
    			put_page(page);
    			page = NULL;
    			if (err == -EEXIST)
    				goto repeat;
    		}
    	}
    
    	return page;
    }
    EXPORT_SYMBOL(pagecache_get_page);
    
    /**
     * find_get_entries - gang pagecache lookup
     * @mapping:	The address_space to search
     * @start:	The starting page cache index
     * @nr_entries:	The maximum number of entries
     * @entries:	Where the resulting entries are placed
     * @indices:	The cache indices corresponding to the entries in @entries
     *
     * find_get_entries() will search for and return a group of up to
     * @nr_entries entries in the mapping.  The entries are placed at
     * @entries.  find_get_entries() takes a reference against any actual
     * pages it returns.
     *
     * The search returns a group of mapping-contiguous page cache entries
     * with ascending indexes.  There may be holes in the indices due to
     * not-present pages.
     *
     * Any shadow entries of evicted pages, or swap entries from
     * shmem/tmpfs, are included in the returned array.
     *
     * find_get_entries() returns the number of pages and shadow entries
     * which were found.
     */
    unsigned find_get_entries(struct address_space *mapping,
    			  pgoff_t start, unsigned int nr_entries,
    			  struct page **entries, pgoff_t *indices)
    {
    	void **slot;
    	unsigned int ret = 0;
    	struct radix_tree_iter iter;
    
    	if (!nr_entries)
    		return 0;
    
    	rcu_read_lock();
    	radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
    		struct page *head, *page;
    repeat:
    		page = radix_tree_deref_slot(slot);
    		if (unlikely(!page))
    			continue;
    		if (radix_tree_exception(page)) {
    			if (radix_tree_deref_retry(page)) {
    				slot = radix_tree_iter_retry(&iter);
    				continue;
    			}
    			/*
    			 * A shadow entry of a recently evicted page, a swap
    			 * entry from shmem/tmpfs or a DAX entry.  Return it
    			 * without attempting to raise page count.
    			 */
    			goto export;
    		}
    
    		head = compound_head(page);
    		if (!page_cache_get_speculative(head))
    			goto repeat;
    
    		/* The page was split under us? */
    		if (compound_head(page) != head) {
    			put_page(head);
    			goto repeat;
    		}
    
    		/* Has the page moved? */
    		if (unlikely(page != *slot)) {
    			put_page(head);
    			goto repeat;
    		}
    export:
    		indices[ret] = iter.index;
    		entries[ret] = page;
    		if (++ret == nr_entries)
    			break;
    	}
    	rcu_read_unlock();
    	return ret;
    }
    
    /**
     * find_get_pages - gang pagecache lookup
     * @mapping:	The address_space to search
     * @start:	The starting page index
     * @nr_pages:	The maximum number of pages
     * @pages:	Where the resulting pages are placed
     *
     * find_get_pages() will search for and return a group of up to
     * @nr_pages pages in the mapping.  The pages are placed at @pages.
     * find_get_pages() takes a reference against the returned pages.
     *
     * The search returns a group of mapping-contiguous pages with ascending
     * indexes.  There may be holes in the indices due to not-present pages.
     *
     * find_get_pages() returns the number of pages which were found.
     */
    unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
    			    unsigned int nr_pages, struct page **pages)
    {
    	struct radix_tree_iter iter;
    	void **slot;
    	unsigned ret = 0;
    
    	if (unlikely(!nr_pages))
    		return 0;
    
    	rcu_read_lock();
    	radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
    		struct page *head, *page;
    repeat:
    		page = radix_tree_deref_slot(slot);
    		if (unlikely(!page))
    			continue;
    
    		if (radix_tree_exception(page)) {
    			if (radix_tree_deref_retry(page)) {
    				slot = radix_tree_iter_retry(&iter);
    				continue;
    			}
    			/*
    			 * A shadow entry of a recently evicted page,
    			 * or a swap entry from shmem/tmpfs.  Skip
    			 * over it.
    			 */
    			continue;
    		}
    
    		head = compound_head(page);
    		if (!page_cache_get_speculative(head))
    			goto repeat;
    
    		/* The page was split under us? */
    		if (compound_head(page) != head) {
    			put_page(head);
    			goto repeat;
    		}
    
    		/* Has the page moved? */
    		if (unlikely(page != *slot)) {
    			put_page(head);
    			goto repeat;
    		}
    
    		pages[ret] = page;
    		if (++ret == nr_pages)
    			break;
    	}
    
    	rcu_read_unlock();
    	return ret;
    }
    
    /**
     * find_get_pages_contig - gang contiguous pagecache lookup
     * @mapping:	The address_space to search
     * @index:	The starting page index
     * @nr_pages:	The maximum number of pages
     * @pages:	Where the resulting pages are placed
     *
     * find_get_pages_contig() works exactly like find_get_pages(), except
     * that the returned number of pages are guaranteed to be contiguous.
     *
     * find_get_pages_contig() returns the number of pages which were found.
     */
    unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
    			       unsigned int nr_pages, struct page **pages)
    {
    	struct radix_tree_iter iter;
    	void **slot;
    	unsigned int ret = 0;
    
    	if (unlikely(!nr_pages))
    		return 0;
    
    	rcu_read_lock();
    	radix_tree_for_each_contig(slot, &mapping->page_tree, &iter, index) {
    		struct page *head, *page;
    repeat:
    		page = radix_tree_deref_slot(slot);
    		/* The hole, there no reason to continue */
    		if (unlikely(!page))
    			break;
    
    		if (radix_tree_exception(page)) {
    			if (radix_tree_deref_retry(page)) {
    				slot = radix_tree_iter_retry(&iter);
    				continue;
    			}
    			/*
    			 * A shadow entry of a recently evicted page,
    			 * or a swap entry from shmem/tmpfs.  Stop
    			 * looking for contiguous pages.
    			 */
    			break;
    		}
    
    		head = compound_head(page);
    		if (!page_cache_get_speculative(head))
    			goto repeat;
    
    		/* The page was split under us? */
    		if (compound_head(page) != head) {
    			put_page(head);
    			goto repeat;
    		}
    
    		/* Has the page moved? */
    		if (unlikely(page != *slot)) {
    			put_page(head);
    			goto repeat;
    		}
    
    		/*
    		 * must check mapping and index after taking the ref.
    		 * otherwise we can get both false positives and false
    		 * negatives, which is just confusing to the caller.
    		 */
    		if (page->mapping == NULL || page_to_pgoff(page) != iter.index) {
    			put_page(page);
    			break;
    		}
    
    		pages[ret] = page;
    		if (++ret == nr_pages)
    			break;
    	}
    	rcu_read_unlock();
    	return ret;
    }
    EXPORT_SYMBOL(find_get_pages_contig);
    
    /**
     * find_get_pages_tag - find and return pages that match @tag
     * @mapping:	the address_space to search
     * @index:	the starting page index
     * @tag:	the tag index
     * @nr_pages:	the maximum number of pages
     * @pages:	where the resulting pages are placed
     *
     * Like find_get_pages, except we only return pages which are tagged with
     * @tag.   We update @index to index the next page for the traversal.
     */
    unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
    			int tag, unsigned int nr_pages, struct page **pages)
    {
    	struct radix_tree_iter iter;
    	void **slot;
    	unsigned ret = 0;
    
    	if (unlikely(!nr_pages))
    		return 0;
    
    	rcu_read_lock();
    	radix_tree_for_each_tagged(slot, &mapping->page_tree,
    				   &iter, *index, tag) {
    		struct page *head, *page;
    repeat:
    		page = radix_tree_deref_slot(slot);
    		if (unlikely(!page))
    			continue;
    
    		if (radix_tree_exception(page)) {
    			if (radix_tree_deref_retry(page)) {
    				slot = radix_tree_iter_retry(&iter);
    				continue;
    			}
    			/*
    			 * A shadow entry of a recently evicted page.
    			 *
    			 * Those entries should never be tagged, but
    			 * this tree walk is lockless and the tags are
    			 * looked up in bulk, one radix tree node at a
    			 * time, so there is a sizable window for page
    			 * reclaim to evict a page we saw tagged.
    			 *
    			 * Skip over it.
    			 */
    			continue;
    		}
    
    		head = compound_head(page);
    		if (!page_cache_get_speculative(head))
    			goto repeat;
    
    		/* The page was split under us? */
    		if (compound_head(page) != head) {
    			put_page(head);
    			goto repeat;
    		}
    
    		/* Has the page moved? */
    		if (unlikely(page != *slot)) {
    			put_page(head);
    			goto repeat;
    		}
    
    		pages[ret] = page;
    		if (++ret == nr_pages)
    			break;
    	}
    
    	rcu_read_unlock();
    
    	if (ret)
    		*index = pages[ret - 1]->index + 1;
    
    	return ret;
    }
    EXPORT_SYMBOL(find_get_pages_tag);
    
    /**
     * find_get_entries_tag - find and return entries that match @tag
     * @mapping:	the address_space to search
     * @start:	the starting page cache index
     * @tag:	the tag index
     * @nr_entries:	the maximum number of entries
     * @entries:	where the resulting entries are placed
     * @indices:	the cache indices corresponding to the entries in @entries
     *
     * Like find_get_entries, except we only return entries which are tagged with
     * @tag.
     */
    unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
    			int tag, unsigned int nr_entries,
    			struct page **entries, pgoff_t *indices)
    {
    	void **slot;
    	unsigned int ret = 0;
    	struct radix_tree_iter iter;
    
    	if (!nr_entries)
    		return 0;
    
    	rcu_read_lock();
    	radix_tree_for_each_tagged(slot, &mapping->page_tree,
    				   &iter, start, tag) {
    		struct page *head, *page;
    repeat:
    		page = radix_tree_deref_slot(slot);
    		if (unlikely(!page))
    			continue;
    		if (radix_tree_exception(page)) {
    			if (radix_tree_deref_retry(page)) {
    				slot = radix_tree_iter_retry(&iter);
    				continue;
    			}
    
    			/*
    			 * A shadow entry of a recently evicted page, a swap
    			 * entry from shmem/tmpfs or a DAX entry.  Return it
    			 * without attempting to raise page count.
    			 */
    			goto export;
    		}
    
    		head = compound_head(page);
    		if (!page_cache_get_speculative(head))
    			goto repeat;
    
    		/* The page was split under us? */
    		if (compound_head(page) != head) {
    			put_page(head);
    			goto repeat;
    		}
    
    		/* Has the page moved? */
    		if (unlikely(page != *slot)) {
    			put_page(head);
    			goto repeat;
    		}
    export:
    		indices[ret] = iter.index;
    		entries[ret] = page;
    		if (++ret == nr_entries)
    			break;
    	}
    	rcu_read_unlock();
    	return ret;
    }
    EXPORT_SYMBOL(find_get_entries_tag);
    
    /*
     * CD/DVDs are error prone. When a medium error occurs, the driver may fail
     * a _large_ part of the i/o request. Imagine the worst scenario:
     *
     *      ---R__________________________________________B__________
     *         ^ reading here                             ^ bad block(assume 4k)
     *
     * read(R) => miss => readahead(R...B) => media error => frustrating retries
     * => failing the whole request => read(R) => read(R+1) =>
     * readahead(R+1...B+1) => bang => read(R+2) => read(R+3) =>
     * readahead(R+3...B+2) => bang => read(R+3) => read(R+4) =>
     * readahead(R+4...B+3) => bang => read(R+4) => read(R+5) => ......
     *
     * It is going insane. Fix it by quickly scaling down the readahead size.
     */
    static void shrink_readahead_size_eio(struct file *filp,
    					struct file_ra_state *ra)
    {
    	ra->ra_pages /= 4;
    }
    
    /**
     * do_generic_file_read - generic file read routine
     * @filp:	the file to read
     * @ppos:	current file position
     * @iter:	data destination
     * @written:	already copied
     *
     * This is a generic file read routine, and uses the
     * mapping->a_ops->readpage() function for the actual low-level stuff.
     *
     * This is really ugly. But the goto's actually try to clarify some
     * of the logic when it comes to error handling etc.
     */
    static ssize_t do_generic_file_read(struct file *filp, loff_t *ppos,
    		struct iov_iter *iter, ssize_t written)
    {
    	struct address_space *mapping = filp->f_mapping;
    	struct inode *inode = mapping->host;
    	struct file_ra_state *ra = &filp->f_ra;
    	pgoff_t index;
    	pgoff_t last_index;
    	pgoff_t prev_index;
    	unsigned long offset;      /* offset into pagecache page */
    	unsigned int prev_offset;
    	int error = 0;
    
    	if (unlikely(*ppos >= inode->i_sb->s_maxbytes))
    		return -EINVAL;
    	iov_iter_truncate(iter, inode->i_sb->s_maxbytes);
    
    	index = *ppos >> PAGE_SHIFT;
    	prev_index = ra->prev_pos >> PAGE_SHIFT;
    	prev_offset = ra->prev_pos & (PAGE_SIZE-1);
    	last_index = (*ppos + iter->count + PAGE_SIZE-1) >> PAGE_SHIFT;
    	offset = *ppos & ~PAGE_MASK;
    
    	for (;;) {
    		struct page *page;
    		pgoff_t end_index;
    		loff_t isize;
    		unsigned long nr, ret;
    
    		cond_resched();
    find_page:
    		page = find_get_page(mapping, index);
    		if (!page) {
    			page_cache_sync_readahead(mapping,
    					ra, filp,
    					index, last_index - index);
    			page = find_get_page(mapping, index);
    			if (unlikely(page == NULL))
    				goto no_cached_page;
    		}
    		if (PageReadahead(page)) {
    			page_cache_async_readahead(mapping,
    					ra, filp, page,
    					index, last_index - index);
    		}
    		if (!PageUptodate(page)) {
    			/*
    			 * See comment in do_read_cache_page on why
    			 * wait_on_page_locked is used to avoid unnecessarily
    			 * serialisations and why it's safe.
    			 */
    			error = wait_on_page_locked_killable(page);
    			if (unlikely(error))
    				goto readpage_error;
    			if (PageUptodate(page))
    				goto page_ok;
    
    			if (inode->i_blkbits == PAGE_SHIFT ||
    					!mapping->a_ops->is_partially_uptodate)
    				goto page_not_up_to_date;
    			if (!trylock_page(page))
    				goto page_not_up_to_date;
    			/* Did it get truncated before we got the lock? */
    			if (!page->mapping)
    				goto page_not_up_to_date_locked;
    			if (!mapping->a_ops->is_partially_uptodate(page,
    							offset, iter->count))
    				goto page_not_up_to_date_locked;
    			unlock_page(page);
    		}
    page_ok:
    		/*
    		 * i_size must be checked after we know the page is Uptodate.
    		 *
    		 * Checking i_size after the check allows us to calculate
    		 * the correct value for "nr", which means the zero-filled
    		 * part of the page is not copied back to userspace (unless
    		 * another truncate extends the file - this is desired though).
    		 */
    
    		isize = i_size_read(inode);
    		end_index = (isize - 1) >> PAGE_SHIFT;
    		if (unlikely(!isize || index > end_index)) {
    			put_page(page);
    			goto out;
    		}
    
    		/* nr is the maximum number of bytes to copy from this page */
    		nr = PAGE_SIZE;
    		if (index == end_index) {
    			nr = ((isize - 1) & ~PAGE_MASK) + 1;
    			if (nr <= offset) {
    				put_page(page);
    				goto out;
    			}
    		}
    		nr = nr - offset;
    
    		/* If users can be writing to this page using arbitrary
    		 * virtual addresses, take care about potential aliasing
    		 * before reading the page on the kernel side.
    		 */
    		if (mapping_writably_mapped(mapping))
    			flush_dcache_page(page);
    
    		/*
    		 * When a sequential read accesses a page several times,
    		 * only mark it as accessed the first time.
    		 */
    		if (prev_index != index || offset != prev_offset)
    			mark_page_accessed(page);
    		prev_index = index;
    
    		/*
    		 * Ok, we have the page, and it's up-to-date, so
    		 * now we can copy it to user space...
    		 */
    
    		ret = copy_page_to_iter(page, offset, nr, iter);
    		offset += ret;
    		index += offset >> PAGE_SHIFT;
    		offset &= ~PAGE_MASK;
    		prev_offset = offset;
    
    		put_page(page);
    		written += ret;
    		if (!iov_iter_count(iter))
    			goto out;
    		if (ret < nr) {
    			error = -EFAULT;
    			goto out;
    		}
    		continue;
    
    page_not_up_to_date:
    		/* Get exclusive access to the page ... */
    		error = lock_page_killable(page);
    		if (unlikely(error))
    			goto readpage_error;
    
    page_not_up_to_date_locked:
    		/* Did it get truncated before we got the lock? */
    		if (!page->mapping) {
    			unlock_page(page);
    			put_page(page);
    			continue;
    		}
    
    		/* Did somebody else fill it already? */
    		if (PageUptodate(page)) {
    			unlock_page(page);
    			goto page_ok;
    		}
    
    readpage:
    		/*
    		 * A previous I/O error may have been due to temporary
    		 * failures, eg. multipath errors.
    		 * PG_error will be set again if readpage fails.
    		 */
    		ClearPageError(page);
    		/* Start the actual read. The read will unlock the page. */
    		error = mapping->a_ops->readpage(filp, page);
    
    		if (unlikely(error)) {
    			if (error == AOP_TRUNCATED_PAGE) {
    				put_page(page);
    				error = 0;
    				goto find_page;
    			}
    			goto readpage_error;
    		}
    
    		if (!PageUptodate(page)) {
    			error = lock_page_killable(page);
    			if (unlikely(error))
    				goto readpage_error;
    			if (!PageUptodate(page)) {
    				if (page->mapping == NULL) {
    					/*
    					 * invalidate_mapping_pages got it
    					 */
    					unlock_page(page);
    					put_page(page);
    					goto find_page;
    				}
    				unlock_page(page);
    				shrink_readahead_size_eio(filp, ra);
    				error = -EIO;
    				goto readpage_error;
    			}
    			unlock_page(page);
    		}
    
    		goto page_ok;
    
    readpage_error:
    		/* UHHUH! A synchronous read error occurred. Report it */
    		put_page(page);
    		goto out;
    
    no_cached_page:
    		/*
    		 * Ok, it wasn't cached, so we need to create a new
    		 * page..
    		 */
    		page = page_cache_alloc_cold(mapping);
    		if (!page) {
    			error = -ENOMEM;
    			goto out;
    		}
    		error = add_to_page_cache_lru(page, mapping, index,
    				mapping_gfp_constraint(mapping, GFP_KERNEL));
    		if (error) {
    			put_page(page);
    			if (error == -EEXIST) {
    				error = 0;
    				goto find_page;
    			}
    			goto out;
    		}
    		goto readpage;
    	}
    
    out:
    	ra->prev_pos = prev_index;
    	ra->prev_pos <<= PAGE_SHIFT;
    	ra->prev_pos |= prev_offset;
    
    	*ppos = ((loff_t)index << PAGE_SHIFT) + offset;
    	file_accessed(filp);
    	return written ? written : error;
    }
    
    /**
     * generic_file_read_iter - generic filesystem read routine
     * @iocb:	kernel I/O control block
     * @iter:	destination for the data read
     *
     * This is the "read_iter()" routine for all filesystems
     * that can use the page cache directly.
     */
    ssize_t
    generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
    {
    	struct file *file = iocb->ki_filp;
    	ssize_t retval = 0;
    	size_t count = iov_iter_count(iter);
    
    	if (!count)
    		goto out; /* skip atime */
    
    	if (iocb->ki_flags & IOCB_DIRECT) {
    		struct address_space *mapping = file->f_mapping;
    		struct inode *inode = mapping->host;
    		struct iov_iter data = *iter;
    		loff_t size;
    
    		size = i_size_read(inode);
    		retval = filemap_write_and_wait_range(mapping, iocb->ki_pos,
    					iocb->ki_pos + count - 1);
    		if (retval < 0)
    			goto out;
    
    		file_accessed(file);
    
    		retval = mapping->a_ops->direct_IO(iocb, &data);
    		if (retval > 0) {
    			iocb->ki_pos += retval;
    			iov_iter_advance(iter, retval);
    		}
    
    		/*
    		 * Btrfs can have a short DIO read if we encounter
    		 * compressed extents, so if there was an error, or if
    		 * we've already read everything we wanted to, or if
    		 * there was a short read because we hit EOF, go ahead
    		 * and return.  Otherwise fallthrough to buffered io for
    		 * the rest of the read.  Buffered reads will not work for
    		 * DAX files, so don't bother trying.
    		 */
    		if (retval < 0 || !iov_iter_count(iter) || iocb->ki_pos >= size ||
    		    IS_DAX(inode))
    			goto out;
    	}
    
    	retval = do_generic_file_read(file, &iocb->ki_pos, iter, retval);
    out:
    	return retval;
    }
    EXPORT_SYMBOL(generic_file_read_iter);
    
    #ifdef CONFIG_MMU
    /**
     * page_cache_read - adds requested page to the page cache if not already there
     * @file:	file to read
     * @offset:	page index
     * @gfp_mask:	memory allocation flags
     *
     * This adds the requested page to the page cache if it isn't already there,
     * and schedules an I/O to read in its contents from disk.
     */
    static int page_cache_read(struct file *file, pgoff_t offset, gfp_t gfp_mask)
    {
    	struct address_space *mapping = file->f_mapping;
    	struct page *page;
    	int ret;
    
    	do {
    		page = __page_cache_alloc(gfp_mask|__GFP_COLD);
    		if (!page)
    			return -ENOMEM;
    
    		ret = add_to_page_cache_lru(page, mapping, offset, gfp_mask & GFP_KERNEL);
    		if (ret == 0)
    			ret = mapping->a_ops->readpage(file, page);
    		else if (ret == -EEXIST)
    			ret = 0; /* losing race to add is OK */
    
    		put_page(page);
    
    	} while (ret == AOP_TRUNCATED_PAGE);
    
    	return ret;
    }
    
    #define MMAP_LOTSAMISS  (100)
    
    /*
     * Synchronous readahead happens when we don't even find
     * a page in the page cache at all.
     */
    static void do_sync_mmap_readahead(struct vm_area_struct *vma,
    				   struct file_ra_state *ra,
    				   struct file *file,
    				   pgoff_t offset)
    {
    	struct address_space *mapping = file->f_mapping;
    
    	/* If we don't want any read-ahead, don't bother */
    	if (vma->vm_flags & VM_RAND_READ)
    		return;
    	if (!ra->ra_pages)
    		return;
    
    	if (vma->vm_flags & VM_SEQ_READ) {
    		page_cache_sync_readahead(mapping, ra, file, offset,
    					  ra->ra_pages);
    		return;
    	}
    
    	/* Avoid banging the cache line if not needed */
    	if (ra->mmap_miss < MMAP_LOTSAMISS * 10)
    		ra->mmap_miss++;
    
    	/*
    	 * Do we miss much more than hit in this file? If so,
    	 * stop bothering with read-ahead. It will only hurt.
    	 */
    	if (ra->mmap_miss > MMAP_LOTSAMISS)
    		return;
    
    	/*
    	 * mmap read-around
    	 */
    	ra->start = max_t(long, 0, offset - ra->ra_pages / 2);
    	ra->size = ra->ra_pages;
    	ra->async_size = ra->ra_pages / 4;
    	ra_submit(ra, mapping, file);
    }
    
    /*
     * Asynchronous readahead happens when we find the page and PG_readahead,
     * so we want to possibly extend the readahead further..
     */
    static void do_async_mmap_readahead(struct vm_area_struct *vma,
    				    struct file_ra_state *ra,
    				    struct file *file,
    				    struct page *page,
    				    pgoff_t offset)
    {
    	struct address_space *mapping = file->f_mapping;
    
    	/* If we don't want any read-ahead, don't bother */
    	if (vma->vm_flags & VM_RAND_READ)
    		return;
    	if (ra->mmap_miss > 0)
    		ra->mmap_miss--;
    	if (PageReadahead(page))
    		page_cache_async_readahead(mapping, ra, file,
    					   page, offset, ra->ra_pages);
    }
    
    /**
     * filemap_fault - read in file data for page fault handling
     * @vma:	vma in which the fault was taken
     * @vmf:	struct vm_fault containing details of the fault
     *
     * filemap_fault() is invoked via the vma operations vector for a
     * mapped memory region to read in file data during a page fault.
     *
     * The goto's are kind of ugly, but this streamlines the normal case of having
     * it in the page cache, and handles the special cases reasonably without
     * having a lot of duplicated code.
     *
     * vma->vm_mm->mmap_sem must be held on entry.
     *
     * If our return value has VM_FAULT_RETRY set, it's because
     * lock_page_or_retry() returned 0.
     * The mmap_sem has usually been released in this case.
     * See __lock_page_or_retry() for the exception.
     *
     * If our return value does not have VM_FAULT_RETRY set, the mmap_sem
     * has not been released.
     *
     * We never return with VM_FAULT_RETRY and a bit from VM_FAULT_ERROR set.
     */
    int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
    {
    	int error;
    	struct file *file = vma->vm_file;
    	struct address_space *mapping = file->f_mapping;
    	struct file_ra_state *ra = &file->f_ra;
    	struct inode *inode = mapping->host;
    	pgoff_t offset = vmf->pgoff;
    	struct page *page;
    	loff_t size;
    	int ret = 0;
    
    	size = round_up(i_size_read(inode), PAGE_SIZE);
    	if (offset >= size >> PAGE_SHIFT)
    		return VM_FAULT_SIGBUS;
    
    	/*
    	 * Do we have something in the page cache already?
    	 */
    	page = find_get_page(mapping, offset);
    	if (likely(page) && !(vmf->flags & FAULT_FLAG_TRIED)) {
    		/*
    		 * We found the page, so try async readahead before
    		 * waiting for the lock.
    		 */
    		do_async_mmap_readahead(vma, ra, file, page, offset);
    	} else if (!page) {
    		/* No page in the page cache at all */
    		do_sync_mmap_readahead(vma, ra, file, offset);
    		count_vm_event(PGMAJFAULT);
    		mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
    		ret = VM_FAULT_MAJOR;
    retry_find:
    		page = find_get_page(mapping, offset);
    		if (!page)
    			goto no_cached_page;
    	}
    
    	if (!lock_page_or_retry(page, vma->vm_mm, vmf->flags)) {
    		put_page(page);
    		return ret | VM_FAULT_RETRY;
    	}
    
    	/* Did it get truncated? */
    	if (unlikely(page->mapping != mapping)) {
    		unlock_page(page);
    		put_page(page);
    		goto retry_find;
    	}
    	VM_BUG_ON_PAGE(page->index != offset, page);
    
    	/*
    	 * We have a locked page in the page cache, now we need to check
    	 * that it's up-to-date. If not, it is going to be due to an error.
    	 */
    	if (unlikely(!PageUptodate(page)))
    		goto page_not_uptodate;
    
    	/*
    	 * Found the page and have a reference on it.
    	 * We must recheck i_size under page lock.
    	 */
    	size = round_up(i_size_read(inode), PAGE_SIZE);
    	if (unlikely(offset >= size >> PAGE_SHIFT)) {
    		unlock_page(page);
    		put_page(page);
    		return VM_FAULT_SIGBUS;
    	}
    
    	vmf->page = page;
    	return ret | VM_FAULT_LOCKED;
    
    no_cached_page:
    	/*
    	 * We're only likely to ever get here if MADV_RANDOM is in
    	 * effect.
    	 */
    	error = page_cache_read(file, offset, vmf->gfp_mask);
    
    	/*
    	 * The page we want has now been added to the page cache.
    	 * In the unlikely event that someone removed it in the
    	 * meantime, we'll just come back here and read it again.
    	 */
    	if (error >= 0)
    		goto retry_find;
    
    	/*
    	 * An error return from page_cache_read can result if the
    	 * system is low on memory, or a problem occurs while trying
    	 * to schedule I/O.
    	 */
    	if (error == -ENOMEM)
    		return VM_FAULT_OOM;
    	return VM_FAULT_SIGBUS;
    
    page_not_uptodate:
    	/*
    	 * Umm, take care of errors if the page isn't up-to-date.
    	 * Try to re-read it _once_. We do this synchronously,
    	 * because there really aren't any performance issues here
    	 * and we need to check for errors.
    	 */
    	ClearPageError(page);
    	error = mapping->a_ops->readpage(file, page);
    	if (!error) {
    		wait_on_page_locked(page);
    		if (!PageUptodate(page))
    			error = -EIO;
    	}
    	put_page(page);
    
    	if (!error || error == AOP_TRUNCATED_PAGE)
    		goto retry_find;
    
    	/* Things didn't work out. Return zero to tell the mm layer so. */
    	shrink_readahead_size_eio(file, ra);
    	return VM_FAULT_SIGBUS;
    }
    EXPORT_SYMBOL(filemap_fault);
    
    void filemap_map_pages(struct fault_env *fe,
    		pgoff_t start_pgoff, pgoff_t end_pgoff)
    {
    	struct radix_tree_iter iter;
    	void **slot;
    	struct file *file = fe->vma->vm_file;
    	struct address_space *mapping = file->f_mapping;
    	pgoff_t last_pgoff = start_pgoff;
    	loff_t size;
    	struct page *head, *page;
    
    	rcu_read_lock();
    	radix_tree_for_each_slot(slot, &mapping->page_tree, &iter,
    			start_pgoff) {
    		if (iter.index > end_pgoff)
    			break;
    repeat:
    		page = radix_tree_deref_slot(slot);
    		if (unlikely(!page))
    			goto next;
    		if (radix_tree_exception(page)) {
    			if (radix_tree_deref_retry(page)) {
    				slot = radix_tree_iter_retry(&iter);
    				continue;
    			}
    			goto next;
    		}
    
    		head = compound_head(page);
    		if (!page_cache_get_speculative(head))
    			goto repeat;
    
    		/* The page was split under us? */
    		if (compound_head(page) != head) {
    			put_page(head);
    			goto repeat;
    		}
    
    		/* Has the page moved? */
    		if (unlikely(page != *slot)) {
    			put_page(head);
    			goto repeat;
    		}
    
    		if (!PageUptodate(page) ||
    				PageReadahead(page) ||
    				PageHWPoison(page))
    			goto skip;
    		if (!trylock_page(page))
    			goto skip;
    
    		if (page->mapping != mapping || !PageUptodate(page))
    			goto unlock;
    
    		size = round_up(i_size_read(mapping->host), PAGE_SIZE);
    		if (page->index >= size >> PAGE_SHIFT)
    			goto unlock;
    
    		if (file->f_ra.mmap_miss > 0)
    			file->f_ra.mmap_miss--;
    
    		fe->address += (iter.index - last_pgoff) << PAGE_SHIFT;
    		if (fe->pte)
    			fe->pte += iter.index - last_pgoff;
    		last_pgoff = iter.index;
    		if (alloc_set_pte(fe, NULL, page))
    			goto unlock;
    		unlock_page(page);
    		goto next;
    unlock:
    		unlock_page(page);
    skip:
    		put_page(page);
    next:
    		/* Huge page is mapped? No need to proceed. */
    		if (pmd_trans_huge(*fe->pmd))
    			break;
    		if (iter.index == end_pgoff)
    			break;
    	}
    	rcu_read_unlock();
    }
    EXPORT_SYMBOL(filemap_map_pages);
    
    int filemap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
    {
    	struct page *page = vmf->page;
    	struct inode *inode = file_inode(vma->vm_file);
    	int ret = VM_FAULT_LOCKED;
    
    	sb_start_pagefault(inode->i_sb);
    	file_update_time(vma->vm_file);
    	lock_page(page);
    	if (page->mapping != inode->i_mapping) {
    		unlock_page(page);
    		ret = VM_FAULT_NOPAGE;
    		goto out;
    	}
    	/*
    	 * We mark the page dirty already here so that when freeze is in
    	 * progress, we are guaranteed that writeback during freezing will
    	 * see the dirty page and writeprotect it again.
    	 */
    	set_page_dirty(page);
    	wait_for_stable_page(page);
    out:
    	sb_end_pagefault(inode->i_sb);
    	return ret;
    }
    EXPORT_SYMBOL(filemap_page_mkwrite);
    
    const struct vm_operations_struct generic_file_vm_ops = {
    	.fault		= filemap_fault,
    	.map_pages	= filemap_map_pages,
    	.page_mkwrite	= filemap_page_mkwrite,
    };
    
    /* This is used for a general mmap of a disk file */
    
    int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
    {
    	struct address_space *mapping = file->f_mapping;
    
    	if (!mapping->a_ops->readpage)
    		return -ENOEXEC;
    	file_accessed(file);
    	vma->vm_ops = &generic_file_vm_ops;
    	return 0;
    }
    
    /*
     * This is for filesystems which do not implement ->writepage.
     */
    int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
    {
    	if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
    		return -EINVAL;
    	return generic_file_mmap(file, vma);
    }
    #else
    int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
    {
    	return -ENOSYS;
    }
    int generic_file_readonly_mmap(struct file * file, struct vm_area_struct * vma)
    {
    	return -ENOSYS;
    }
    #endif /* CONFIG_MMU */
    
    EXPORT_SYMBOL(generic_file_mmap);
    EXPORT_SYMBOL(generic_file_readonly_mmap);
    
    static struct page *wait_on_page_read(struct page *page)
    {
    	if (!IS_ERR(page)) {
    		wait_on_page_locked(page);
    		if (!PageUptodate(page)) {
    			put_page(page);
    			page = ERR_PTR(-EIO);
    		}
    	}
    	return page;
    }
    
    static struct page *do_read_cache_page(struct address_space *mapping,
    				pgoff_t index,
    				int (*filler)(void *, struct page *),
    				void *data,
    				gfp_t gfp)
    {
    	struct page *page;
    	int err;
    repeat:
    	page = find_get_page(mapping, index);
    	if (!page) {
    		page = __page_cache_alloc(gfp | __GFP_COLD);
    		if (!page)
    			return ERR_PTR(-ENOMEM);
    		err = add_to_page_cache_lru(page, mapping, index, gfp);
    		if (unlikely(err)) {
    			put_page(page);
    			if (err == -EEXIST)
    				goto repeat;
    			/* Presumably ENOMEM for radix tree node */
    			return ERR_PTR(err);
    		}
    
    filler:
    		err = filler(data, page);
    		if (err < 0) {
    			put_page(page);
    			return ERR_PTR(err);
    		}
    
    		page = wait_on_page_read(page);
    		if (IS_ERR(page))
    			return page;
    		goto out;
    	}
    	if (PageUptodate(page))
    		goto out;
    
    	/*
    	 * Page is not up to date and may be locked due one of the following
    	 * case a: Page is being filled and the page lock is held
    	 * case b: Read/write error clearing the page uptodate status
    	 * case c: Truncation in progress (page locked)
    	 * case d: Reclaim in progress
    	 *
    	 * Case a, the page will be up to date when the page is unlocked.
    	 *    There is no need to serialise on the page lock here as the page
    	 *    is pinned so the lock gives no additional protection. Even if the
    	 *    the page is truncated, the data is still valid if PageUptodate as
    	 *    it's a race vs truncate race.
    	 * Case b, the page will not be up to date
    	 * Case c, the page may be truncated but in itself, the data may still
    	 *    be valid after IO completes as it's a read vs truncate race. The
    	 *    operation must restart if the page is not uptodate on unlock but
    	 *    otherwise serialising on page lock to stabilise the mapping gives
    	 *    no additional guarantees to the caller as the page lock is
    	 *    released before return.
    	 * Case d, similar to truncation. If reclaim holds the page lock, it
    	 *    will be a race with remove_mapping that determines if the mapping
    	 *    is valid on unlock but otherwise the data is valid and there is
    	 *    no need to serialise with page lock.
    	 *
    	 * As the page lock gives no additional guarantee, we optimistically
    	 * wait on the page to be unlocked and check if it's up to date and
    	 * use the page if it is. Otherwise, the page lock is required to
    	 * distinguish between the different cases. The motivation is that we
    	 * avoid spurious serialisations and wakeups when multiple processes
    	 * wait on the same page for IO to complete.
    	 */
    	wait_on_page_locked(page);
    	if (PageUptodate(page))
    		goto out;
    
    	/* Distinguish between all the cases under the safety of the lock */
    	lock_page(page);
    
    	/* Case c or d, restart the operation */
    	if (!page->mapping) {
    		unlock_page(page);
    		put_page(page);
    		goto repeat;
    	}
    
    	/* Someone else locked and filled the page in a very small window */
    	if (PageUptodate(page)) {
    		unlock_page(page);
    		goto out;
    	}
    	goto filler;
    
    out:
    	mark_page_accessed(page);
    	return page;
    }
    
    /**
     * read_cache_page - read into page cache, fill it if needed
     * @mapping:	the page's address_space
     * @index:	the page index
     * @filler:	function to perform the read
     * @data:	first arg to filler(data, page) function, often left as NULL
     *
     * Read into the page cache. If a page already exists, and PageUptodate() is
     * not set, try to fill the page and wait for it to become unlocked.
     *
     * If the page does not get brought uptodate, return -EIO.
     */
    struct page *read_cache_page(struct address_space *mapping,
    				pgoff_t index,
    				int (*filler)(void *, struct page *),
    				void *data)
    {
    	return do_read_cache_page(mapping, index, filler, data, mapping_gfp_mask(mapping));
    }
    EXPORT_SYMBOL(read_cache_page);
    
    /**
     * read_cache_page_gfp - read into page cache, using specified page allocation flags.
     * @mapping:	the page's address_space
     * @index:	the page index
     * @gfp:	the page allocator flags to use if allocating
     *
     * This is the same as "read_mapping_page(mapping, index, NULL)", but with
     * any new page allocations done using the specified allocation flags.
     *
     * If the page does not get brought uptodate, return -EIO.
     */
    struct page *read_cache_page_gfp(struct address_space *mapping,
    				pgoff_t index,
    				gfp_t gfp)
    {
    	filler_t *filler = (filler_t *)mapping->a_ops->readpage;
    
    	return do_read_cache_page(mapping, index, filler, NULL, gfp);
    }
    EXPORT_SYMBOL(read_cache_page_gfp);
    
    /*
     * Performs necessary checks before doing a write
     *
     * Can adjust writing position or amount of bytes to write.
     * Returns appropriate error code that caller should return or
     * zero in case that write should be allowed.
     */
    inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
    {
    	struct file *file = iocb->ki_filp;
    	struct inode *inode = file->f_mapping->host;
    	unsigned long limit = rlimit(RLIMIT_FSIZE);
    	loff_t pos;
    
    	if (!iov_iter_count(from))
    		return 0;
    
    	/* FIXME: this is for backwards compatibility with 2.4 */
    	if (iocb->ki_flags & IOCB_APPEND)
    		iocb->ki_pos = i_size_read(inode);
    
    	pos = iocb->ki_pos;
    
    	if (limit != RLIM_INFINITY) {
    		if (iocb->ki_pos >= limit) {
    			send_sig(SIGXFSZ, current, 0);
    			return -EFBIG;
    		}
    		iov_iter_truncate(from, limit - (unsigned long)pos);
    	}
    
    	/*
    	 * LFS rule
    	 */
    	if (unlikely(pos + iov_iter_count(from) > MAX_NON_LFS &&
    				!(file->f_flags & O_LARGEFILE))) {
    		if (pos >= MAX_NON_LFS)
    			return -EFBIG;
    		iov_iter_truncate(from, MAX_NON_LFS - (unsigned long)pos);
    	}
    
    	/*
    	 * Are we about to exceed the fs block limit ?
    	 *
    	 * If we have written data it becomes a short write.  If we have
    	 * exceeded without writing data we send a signal and return EFBIG.
    	 * Linus frestrict idea will clean these up nicely..
    	 */
    	if (unlikely(pos >= inode->i_sb->s_maxbytes))
    		return -EFBIG;
    
    	iov_iter_truncate(from, inode->i_sb->s_maxbytes - pos);
    	return iov_iter_count(from);
    }
    EXPORT_SYMBOL(generic_write_checks);
    
    int pagecache_write_begin(struct file *file, struct address_space *mapping,
    				loff_t pos, unsigned len, unsigned flags,
    				struct page **pagep, void **fsdata)
    {
    	const struct address_space_operations *aops = mapping->a_ops;
    
    	return aops->write_begin(file, mapping, pos, len, flags,
    							pagep, fsdata);
    }
    EXPORT_SYMBOL(pagecache_write_begin);
    
    int pagecache_write_end(struct file *file, struct address_space *mapping,
    				loff_t pos, unsigned len, unsigned copied,
    				struct page *page, void *fsdata)
    {
    	const struct address_space_operations *aops = mapping->a_ops;
    
    	return aops->write_end(file, mapping, pos, len, copied, page, fsdata);
    }
    EXPORT_SYMBOL(pagecache_write_end);
    
    ssize_t
    generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
    {
    	struct file	*file = iocb->ki_filp;
    	struct address_space *mapping = file->f_mapping;
    	struct inode	*inode = mapping->host;
    	loff_t		pos = iocb->ki_pos;
    	ssize_t		written;
    	size_t		write_len;
    	pgoff_t		end;
    	struct iov_iter data;
    
    	write_len = iov_iter_count(from);
    	end = (pos + write_len - 1) >> PAGE_SHIFT;
    
    	written = filemap_write_and_wait_range(mapping, pos, pos + write_len - 1);
    	if (written)
    		goto out;
    
    	/*
    	 * After a write we want buffered reads to be sure to go to disk to get
    	 * the new data.  We invalidate clean cached page from the region we're
    	 * about to write.  We do this *before* the write so that we can return
    	 * without clobbering -EIOCBQUEUED from ->direct_IO().
    	 */
    	if (mapping->nrpages) {
    		written = invalidate_inode_pages2_range(mapping,
    					pos >> PAGE_SHIFT, end);
    		/*
    		 * If a page can not be invalidated, return 0 to fall back
    		 * to buffered write.
    		 */
    		if (written) {
    			if (written == -EBUSY)
    				return 0;
    			goto out;
    		}
    	}
    
    	data = *from;
    	written = mapping->a_ops->direct_IO(iocb, &data);
    
    	/*
    	 * Finally, try again to invalidate clean pages which might have been
    	 * cached by non-direct readahead, or faulted in by get_user_pages()
    	 * if the source of the write was an mmap'ed region of the file
    	 * we're writing.  Either one is a pretty crazy thing to do,
    	 * so we don't support it 100%.  If this invalidation
    	 * fails, tough, the write still worked...
    	 */
    	if (mapping->nrpages) {
    		invalidate_inode_pages2_range(mapping,
    					      pos >> PAGE_SHIFT, end);
    	}
    
    	if (written > 0) {
    		pos += written;
    		iov_iter_advance(from, written);
    		if (pos > i_size_read(inode) && !S_ISBLK(inode->i_mode)) {
    			i_size_write(inode, pos);
    			mark_inode_dirty(inode);
    		}
    		iocb->ki_pos = pos;
    	}
    out:
    	return written;
    }
    EXPORT_SYMBOL(generic_file_direct_write);
    
    /*
     * Find or create a page at the given pagecache position. Return the locked
     * page. This function is specifically for buffered writes.
     */
    struct page *grab_cache_page_write_begin(struct address_space *mapping,
    					pgoff_t index, unsigned flags)
    {
    	struct page *page;
    	int fgp_flags = FGP_LOCK|FGP_WRITE|FGP_CREAT;
    
    	if (flags & AOP_FLAG_NOFS)
    		fgp_flags |= FGP_NOFS;
    
    	page = pagecache_get_page(mapping, index, fgp_flags,
    			mapping_gfp_mask(mapping));
    	if (page)
    		wait_for_stable_page(page);
    
    	return page;
    }
    EXPORT_SYMBOL(grab_cache_page_write_begin);
    
    ssize_t generic_perform_write(struct file *file,
    				struct iov_iter *i, loff_t pos)
    {
    	struct address_space *mapping = file->f_mapping;
    	const struct address_space_operations *a_ops = mapping->a_ops;
    	long status = 0;
    	ssize_t written = 0;
    	unsigned int flags = 0;
    
    	/*
    	 * Copies from kernel address space cannot fail (NFSD is a big user).
    	 */
    	if (!iter_is_iovec(i))
    		flags |= AOP_FLAG_UNINTERRUPTIBLE;
    
    	do {
    		struct page *page;
    		unsigned long offset;	/* Offset into pagecache page */
    		unsigned long bytes;	/* Bytes to write to page */
    		size_t copied;		/* Bytes copied from user */
    		void *fsdata;
    
    		offset = (pos & (PAGE_SIZE - 1));
    		bytes = min_t(unsigned long, PAGE_SIZE - offset,
    						iov_iter_count(i));
    
    again:
    		/*
    		 * Bring in the user page that we will copy from _first_.
    		 * Otherwise there's a nasty deadlock on copying from the
    		 * same page as we're writing to, without it being marked
    		 * up-to-date.
    		 *
    		 * Not only is this an optimisation, but it is also required
    		 * to check that the address is actually valid, when atomic
    		 * usercopies are used, below.
    		 */
    		if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
    			status = -EFAULT;
    			break;
    		}
    
    		if (fatal_signal_pending(current)) {
    			status = -EINTR;
    			break;
    		}
    
    		status = a_ops->write_begin(file, mapping, pos, bytes, flags,
    						&page, &fsdata);
    		if (unlikely(status < 0))
    			break;
    
    		if (mapping_writably_mapped(mapping))
    			flush_dcache_page(page);
    
    		copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
    		flush_dcache_page(page);
    
    		status = a_ops->write_end(file, mapping, pos, bytes, copied,
    						page, fsdata);
    		if (unlikely(status < 0))
    			break;
    		copied = status;
    
    		cond_resched();
    
    		iov_iter_advance(i, copied);
    		if (unlikely(copied == 0)) {
    			/*
    			 * If we were unable to copy any data at all, we must
    			 * fall back to a single segment length write.
    			 *
    			 * If we didn't fallback here, we could livelock
    			 * because not all segments in the iov can be copied at
    			 * once without a pagefault.
    			 */
    			bytes = min_t(unsigned long, PAGE_SIZE - offset,
    						iov_iter_single_seg_count(i));
    			goto again;
    		}
    		pos += copied;
    		written += copied;
    
    		balance_dirty_pages_ratelimited(mapping);
    	} while (iov_iter_count(i));
    
    	return written ? written : status;
    }
    EXPORT_SYMBOL(generic_perform_write);
    
    /**
     * __generic_file_write_iter - write data to a file
     * @iocb:	IO state structure (file, offset, etc.)
     * @from:	iov_iter with data to write
     *
     * This function does all the work needed for actually writing data to a
     * file. It does all basic checks, removes SUID from the file, updates
     * modification times and calls proper subroutines depending on whether we
     * do direct IO or a standard buffered write.
     *
     * It expects i_mutex to be grabbed unless we work on a block device or similar
     * object which does not need locking at all.
     *
     * This function does *not* take care of syncing data in case of O_SYNC write.
     * A caller has to handle it. This is mainly due to the fact that we want to
     * avoid syncing under i_mutex.
     */
    ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
    {
    	struct file *file = iocb->ki_filp;
    	struct address_space * mapping = file->f_mapping;
    	struct inode 	*inode = mapping->host;
    	ssize_t		written = 0;
    	ssize_t		err;
    	ssize_t		status;
    
    	/* We can write back this queue in page reclaim */
    	current->backing_dev_info = inode_to_bdi(inode);
    	err = file_remove_privs(file);
    	if (err)
    		goto out;
    
    	err = file_update_time(file);
    	if (err)
    		goto out;
    
    	if (iocb->ki_flags & IOCB_DIRECT) {
    		loff_t pos, endbyte;
    
    		written = generic_file_direct_write(iocb, from);
    		/*
    		 * If the write stopped short of completing, fall back to
    		 * buffered writes.  Some filesystems do this for writes to
    		 * holes, for example.  For DAX files, a buffered write will
    		 * not succeed (even if it did, DAX does not handle dirty
    		 * page-cache pages correctly).
    		 */
    		if (written < 0 || !iov_iter_count(from) || IS_DAX(inode))
    			goto out;
    
    		status = generic_perform_write(file, from, pos = iocb->ki_pos);
    		/*
    		 * If generic_perform_write() returned a synchronous error
    		 * then we want to return the number of bytes which were
    		 * direct-written, or the error code if that was zero.  Note
    		 * that this differs from normal direct-io semantics, which
    		 * will return -EFOO even if some bytes were written.
    		 */
    		if (unlikely(status < 0)) {
    			err = status;
    			goto out;
    		}
    		/*
    		 * We need to ensure that the page cache pages are written to
    		 * disk and invalidated to preserve the expected O_DIRECT
    		 * semantics.
    		 */
    		endbyte = pos + status - 1;
    		err = filemap_write_and_wait_range(mapping, pos, endbyte);
    		if (err == 0) {
    			iocb->ki_pos = endbyte + 1;
    			written += status;
    			invalidate_mapping_pages(mapping,
    						 pos >> PAGE_SHIFT,
    						 endbyte >> PAGE_SHIFT);
    		} else {
    			/*
    			 * We don't know how much we wrote, so just return
    			 * the number of bytes which were direct-written
    			 */
    		}
    	} else {
    		written = generic_perform_write(file, from, iocb->ki_pos);
    		if (likely(written > 0))
    			iocb->ki_pos += written;
    	}
    out:
    	current->backing_dev_info = NULL;
    	return written ? written : err;
    }
    EXPORT_SYMBOL(__generic_file_write_iter);
    
    /**
     * generic_file_write_iter - write data to a file
     * @iocb:	IO state structure
     * @from:	iov_iter with data to write
     *
     * This is a wrapper around __generic_file_write_iter() to be used by most
     * filesystems. It takes care of syncing the file in case of O_SYNC file
     * and acquires i_mutex as needed.
     */
    ssize_t generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
    {
    	struct file *file = iocb->ki_filp;
    	struct inode *inode = file->f_mapping->host;
    	ssize_t ret;
    
    	inode_lock(inode);
    	ret = generic_write_checks(iocb, from);
    	if (ret > 0)
    		ret = __generic_file_write_iter(iocb, from);
    	inode_unlock(inode);
    
    	if (ret > 0)
    		ret = generic_write_sync(iocb, ret);
    	return ret;
    }
    EXPORT_SYMBOL(generic_file_write_iter);
    
    /**
     * try_to_release_page() - release old fs-specific metadata on a page
     *
     * @page: the page which the kernel is trying to free
     * @gfp_mask: memory allocation flags (and I/O mode)
     *
     * The address_space is to try to release any data against the page
     * (presumably at page->private).  If the release was successful, return `1'.
     * Otherwise return zero.
     *
     * This may also be called if PG_fscache is set on a page, indicating that the
     * page is known to the local caching routines.
     *
     * The @gfp_mask argument specifies whether I/O may be performed to release
     * this page (__GFP_IO), and whether the call may block (__GFP_RECLAIM & __GFP_FS).
     *
     */
    int try_to_release_page(struct page *page, gfp_t gfp_mask)
    {
    	struct address_space * const mapping = page->mapping;
    
    	BUG_ON(!PageLocked(page));
    	if (PageWriteback(page))
    		return 0;
    
    	if (mapping && mapping->a_ops->releasepage)
    		return mapping->a_ops->releasepage(page, gfp_mask);
    	return try_to_free_buffers(page);
    }
    
    EXPORT_SYMBOL(try_to_release_page);