Skip to content
Snippets Groups Projects
Select Git revision
  • 1b7b7596aeebc21913bad49eb6a2c364c4b2988a
  • vme-testing default
  • ci-test
  • master
  • remoteproc
  • am625-sk-ov5640
  • pcal6534-upstreaming
  • lps22df-upstreaming
  • msc-upstreaming
  • imx8mp
  • iio/noa1305
  • vme-next
  • vme-next-4.14-rc4
  • v4.14-rc4
  • v4.14-rc3
  • v4.14-rc2
  • v4.14-rc1
  • v4.13
  • vme-next-4.13-rc7
  • v4.13-rc7
  • v4.13-rc6
  • v4.13-rc5
  • v4.13-rc4
  • v4.13-rc3
  • v4.13-rc2
  • v4.13-rc1
  • v4.12
  • v4.12-rc7
  • v4.12-rc6
  • v4.12-rc5
  • v4.12-rc4
  • v4.12-rc3
32 results

i40evf_main.c

Blame
  • swap_state.c 22.42 KiB
    // SPDX-License-Identifier: GPL-2.0
    /*
     *  linux/mm/swap_state.c
     *
     *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
     *  Swap reorganised 29.12.95, Stephen Tweedie
     *
     *  Rewritten to use page cache, (C) 1998 Stephen Tweedie
     */
    #include <linux/mm.h>
    #include <linux/gfp.h>
    #include <linux/kernel_stat.h>
    #include <linux/swap.h>
    #include <linux/swapops.h>
    #include <linux/init.h>
    #include <linux/pagemap.h>
    #include <linux/backing-dev.h>
    #include <linux/blkdev.h>
    #include <linux/pagevec.h>
    #include <linux/migrate.h>
    #include <linux/vmalloc.h>
    #include <linux/swap_slots.h>
    #include <linux/huge_mm.h>
    
    #include <asm/pgtable.h>
    
    /*
     * swapper_space is a fiction, retained to simplify the path through
     * vmscan's shrink_page_list.
     */
    static const struct address_space_operations swap_aops = {
    	.writepage	= swap_writepage,
    	.set_page_dirty	= swap_set_page_dirty,
    #ifdef CONFIG_MIGRATION
    	.migratepage	= migrate_page,
    #endif
    };
    
    struct address_space *swapper_spaces[MAX_SWAPFILES] __read_mostly;
    static unsigned int nr_swapper_spaces[MAX_SWAPFILES] __read_mostly;
    static bool enable_vma_readahead __read_mostly = true;
    
    #define SWAP_RA_WIN_SHIFT	(PAGE_SHIFT / 2)
    #define SWAP_RA_HITS_MASK	((1UL << SWAP_RA_WIN_SHIFT) - 1)
    #define SWAP_RA_HITS_MAX	SWAP_RA_HITS_MASK
    #define SWAP_RA_WIN_MASK	(~PAGE_MASK & ~SWAP_RA_HITS_MASK)
    
    #define SWAP_RA_HITS(v)		((v) & SWAP_RA_HITS_MASK)
    #define SWAP_RA_WIN(v)		(((v) & SWAP_RA_WIN_MASK) >> SWAP_RA_WIN_SHIFT)
    #define SWAP_RA_ADDR(v)		((v) & PAGE_MASK)
    
    #define SWAP_RA_VAL(addr, win, hits)				\
    	(((addr) & PAGE_MASK) |					\
    	 (((win) << SWAP_RA_WIN_SHIFT) & SWAP_RA_WIN_MASK) |	\
    	 ((hits) & SWAP_RA_HITS_MASK))
    
    /* Initial readahead hits is 4 to start up with a small window */
    #define GET_SWAP_RA_VAL(vma)					\
    	(atomic_long_read(&(vma)->swap_readahead_info) ? : 4)
    
    #define INC_CACHE_INFO(x)	do { swap_cache_info.x++; } while (0)
    #define ADD_CACHE_INFO(x, nr)	do { swap_cache_info.x += (nr); } while (0)
    
    static struct {
    	unsigned long add_total;
    	unsigned long del_total;
    	unsigned long find_success;
    	unsigned long find_total;
    } swap_cache_info;
    
    unsigned long total_swapcache_pages(void)
    {
    	unsigned int i, j, nr;
    	unsigned long ret = 0;
    	struct address_space *spaces;
    	struct swap_info_struct *si;
    
    	for (i = 0; i < MAX_SWAPFILES; i++) {
    		swp_entry_t entry = swp_entry(i, 1);
    
    		/* Avoid get_swap_device() to warn for bad swap entry */
    		if (!swp_swap_info(entry))
    			continue;
    		/* Prevent swapoff to free swapper_spaces */
    		si = get_swap_device(entry);
    		if (!si)
    			continue;
    		nr = nr_swapper_spaces[i];
    		spaces = swapper_spaces[i];
    		for (j = 0; j < nr; j++)
    			ret += spaces[j].nrpages;
    		put_swap_device(si);
    	}
    	return ret;
    }
    
    static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
    
    void show_swap_cache_info(void)
    {
    	printk("%lu pages in swap cache\n", total_swapcache_pages());
    	printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
    		swap_cache_info.add_total, swap_cache_info.del_total,
    		swap_cache_info.find_success, swap_cache_info.find_total);
    	printk("Free swap  = %ldkB\n",
    		get_nr_swap_pages() << (PAGE_SHIFT - 10));
    	printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
    }
    
    /*
     * add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
     * but sets SwapCache flag and private instead of mapping and index.
     */
    int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp)
    {
    	struct address_space *address_space = swap_address_space(entry);
    	pgoff_t idx = swp_offset(entry);
    	XA_STATE_ORDER(xas, &address_space->i_pages, idx, compound_order(page));
    	unsigned long i, nr = hpage_nr_pages(page);
    
    	VM_BUG_ON_PAGE(!PageLocked(page), page);
    	VM_BUG_ON_PAGE(PageSwapCache(page), page);
    	VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
    
    	page_ref_add(page, nr);
    	SetPageSwapCache(page);
    
    	do {
    		xas_lock_irq(&xas);
    		xas_create_range(&xas);
    		if (xas_error(&xas))
    			goto unlock;
    		for (i = 0; i < nr; i++) {
    			VM_BUG_ON_PAGE(xas.xa_index != idx + i, page);
    			set_page_private(page + i, entry.val + i);
    			xas_store(&xas, page);
    			xas_next(&xas);
    		}
    		address_space->nrpages += nr;
    		__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, nr);
    		ADD_CACHE_INFO(add_total, nr);
    unlock:
    		xas_unlock_irq(&xas);
    	} while (xas_nomem(&xas, gfp));
    
    	if (!xas_error(&xas))
    		return 0;
    
    	ClearPageSwapCache(page);
    	page_ref_sub(page, nr);
    	return xas_error(&xas);
    }
    
    /*
     * This must be called only on pages that have
     * been verified to be in the swap cache.
     */
    void __delete_from_swap_cache(struct page *page, swp_entry_t entry)
    {
    	struct address_space *address_space = swap_address_space(entry);
    	int i, nr = hpage_nr_pages(page);
    	pgoff_t idx = swp_offset(entry);
    	XA_STATE(xas, &address_space->i_pages, idx);
    
    	VM_BUG_ON_PAGE(!PageLocked(page), page);
    	VM_BUG_ON_PAGE(!PageSwapCache(page), page);
    	VM_BUG_ON_PAGE(PageWriteback(page), page);
    
    	for (i = 0; i < nr; i++) {
    		void *entry = xas_store(&xas, NULL);
    		VM_BUG_ON_PAGE(entry != page, entry);
    		set_page_private(page + i, 0);
    		xas_next(&xas);
    	}
    	ClearPageSwapCache(page);
    	address_space->nrpages -= nr;
    	__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, -nr);
    	ADD_CACHE_INFO(del_total, nr);
    }
    
    /**
     * add_to_swap - allocate swap space for a page
     * @page: page we want to move to swap
     *
     * Allocate swap space for the page and add the page to the
     * swap cache.  Caller needs to hold the page lock. 
     */
    int add_to_swap(struct page *page)
    {
    	swp_entry_t entry;
    	int err;
    
    	VM_BUG_ON_PAGE(!PageLocked(page), page);
    	VM_BUG_ON_PAGE(!PageUptodate(page), page);
    
    	entry = get_swap_page(page);
    	if (!entry.val)
    		return 0;
    
    	/*
    	 * XArray node allocations from PF_MEMALLOC contexts could
    	 * completely exhaust the page allocator. __GFP_NOMEMALLOC
    	 * stops emergency reserves from being allocated.
    	 *
    	 * TODO: this could cause a theoretical memory reclaim
    	 * deadlock in the swap out path.
    	 */
    	/*
    	 * Add it to the swap cache.
    	 */
    	err = add_to_swap_cache(page, entry,
    			__GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
    	if (err)
    		/*
    		 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
    		 * clear SWAP_HAS_CACHE flag.
    		 */
    		goto fail;
    	/*
    	 * Normally the page will be dirtied in unmap because its pte should be
    	 * dirty. A special case is MADV_FREE page. The page'e pte could have
    	 * dirty bit cleared but the page's SwapBacked bit is still set because
    	 * clearing the dirty bit and SwapBacked bit has no lock protected. For
    	 * such page, unmap will not set dirty bit for it, so page reclaim will
    	 * not write the page out. This can cause data corruption when the page
    	 * is swap in later. Always setting the dirty bit for the page solves
    	 * the problem.
    	 */
    	set_page_dirty(page);
    
    	return 1;
    
    fail:
    	put_swap_page(page, entry);
    	return 0;
    }
    
    /*
     * This must be called only on pages that have
     * been verified to be in the swap cache and locked.
     * It will never put the page into the free list,
     * the caller has a reference on the page.
     */
    void delete_from_swap_cache(struct page *page)
    {
    	swp_entry_t entry = { .val = page_private(page) };
    	struct address_space *address_space = swap_address_space(entry);
    
    	xa_lock_irq(&address_space->i_pages);
    	__delete_from_swap_cache(page, entry);
    	xa_unlock_irq(&address_space->i_pages);
    
    	put_swap_page(page, entry);
    	page_ref_sub(page, hpage_nr_pages(page));
    }
    
    /* 
     * If we are the only user, then try to free up the swap cache. 
     * 
     * Its ok to check for PageSwapCache without the page lock
     * here because we are going to recheck again inside
     * try_to_free_swap() _with_ the lock.
     * 					- Marcelo
     */
    static inline void free_swap_cache(struct page *page)
    {
    	if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
    		try_to_free_swap(page);
    		unlock_page(page);
    	}
    }
    
    /* 
     * Perform a free_page(), also freeing any swap cache associated with
     * this page if it is the last user of the page.
     */
    void free_page_and_swap_cache(struct page *page)
    {
    	free_swap_cache(page);
    	if (!is_huge_zero_page(page))
    		put_page(page);
    }
    
    /*
     * Passed an array of pages, drop them all from swapcache and then release
     * them.  They are removed from the LRU and freed if this is their last use.
     */
    void free_pages_and_swap_cache(struct page **pages, int nr)
    {
    	struct page **pagep = pages;
    	int i;
    
    	lru_add_drain();
    	for (i = 0; i < nr; i++)
    		free_swap_cache(pagep[i]);
    	release_pages(pagep, nr);
    }
    
    static inline bool swap_use_vma_readahead(void)
    {
    	return READ_ONCE(enable_vma_readahead) && !atomic_read(&nr_rotate_swap);
    }
    
    /*
     * Lookup a swap entry in the swap cache. A found page will be returned
     * unlocked and with its refcount incremented - we rely on the kernel
     * lock getting page table operations atomic even if we drop the page
     * lock before returning.
     */
    struct page *lookup_swap_cache(swp_entry_t entry, struct vm_area_struct *vma,
    			       unsigned long addr)
    {
    	struct page *page;
    	struct swap_info_struct *si;
    
    	si = get_swap_device(entry);
    	if (!si)
    		return NULL;
    	page = find_get_page(swap_address_space(entry), swp_offset(entry));
    	put_swap_device(si);
    
    	INC_CACHE_INFO(find_total);
    	if (page) {
    		bool vma_ra = swap_use_vma_readahead();
    		bool readahead;
    
    		INC_CACHE_INFO(find_success);
    		/*
    		 * At the moment, we don't support PG_readahead for anon THP
    		 * so let's bail out rather than confusing the readahead stat.
    		 */
    		if (unlikely(PageTransCompound(page)))
    			return page;
    
    		readahead = TestClearPageReadahead(page);
    		if (vma && vma_ra) {
    			unsigned long ra_val;
    			int win, hits;
    
    			ra_val = GET_SWAP_RA_VAL(vma);
    			win = SWAP_RA_WIN(ra_val);
    			hits = SWAP_RA_HITS(ra_val);
    			if (readahead)
    				hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX);
    			atomic_long_set(&vma->swap_readahead_info,
    					SWAP_RA_VAL(addr, win, hits));
    		}
    
    		if (readahead) {
    			count_vm_event(SWAP_RA_HIT);
    			if (!vma || !vma_ra)
    				atomic_inc(&swapin_readahead_hits);
    		}
    	}
    
    	return page;
    }
    
    struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
    			struct vm_area_struct *vma, unsigned long addr,
    			bool *new_page_allocated)
    {
    	struct page *found_page = NULL, *new_page = NULL;
    	struct swap_info_struct *si;
    	int err;
    	*new_page_allocated = false;
    
    	do {
    		/*
    		 * First check the swap cache.  Since this is normally
    		 * called after lookup_swap_cache() failed, re-calling
    		 * that would confuse statistics.
    		 */
    		si = get_swap_device(entry);
    		if (!si)
    			break;
    		found_page = find_get_page(swap_address_space(entry),
    					   swp_offset(entry));
    		put_swap_device(si);
    		if (found_page)
    			break;
    
    		/*
    		 * Just skip read ahead for unused swap slot.
    		 * During swap_off when swap_slot_cache is disabled,
    		 * we have to handle the race between putting
    		 * swap entry in swap cache and marking swap slot
    		 * as SWAP_HAS_CACHE.  That's done in later part of code or
    		 * else swap_off will be aborted if we return NULL.
    		 */
    		if (!__swp_swapcount(entry) && swap_slot_cache_enabled)
    			break;
    
    		/*
    		 * Get a new page to read into from swap.
    		 */
    		if (!new_page) {
    			new_page = alloc_page_vma(gfp_mask, vma, addr);
    			if (!new_page)
    				break;		/* Out of memory */
    		}
    
    		/*
    		 * Swap entry may have been freed since our caller observed it.
    		 */
    		err = swapcache_prepare(entry);
    		if (err == -EEXIST) {
    			/*
    			 * We might race against get_swap_page() and stumble
    			 * across a SWAP_HAS_CACHE swap_map entry whose page
    			 * has not been brought into the swapcache yet.
    			 */
    			cond_resched();
    			continue;
    		} else if (err)		/* swp entry is obsolete ? */
    			break;
    
    		/* May fail (-ENOMEM) if XArray node allocation failed. */
    		__SetPageLocked(new_page);
    		__SetPageSwapBacked(new_page);
    		err = add_to_swap_cache(new_page, entry, gfp_mask & GFP_KERNEL);
    		if (likely(!err)) {
    			/* Initiate read into locked page */
    			SetPageWorkingset(new_page);
    			lru_cache_add_anon(new_page);
    			*new_page_allocated = true;
    			return new_page;
    		}
    		__ClearPageLocked(new_page);
    		/*
    		 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
    		 * clear SWAP_HAS_CACHE flag.
    		 */
    		put_swap_page(new_page, entry);
    	} while (err != -ENOMEM);
    
    	if (new_page)
    		put_page(new_page);
    	return found_page;
    }
    
    /*
     * Locate a page of swap in physical memory, reserving swap cache space
     * and reading the disk if it is not already cached.
     * A failure return means that either the page allocation failed or that
     * the swap entry is no longer in use.
     */
    struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
    		struct vm_area_struct *vma, unsigned long addr, bool do_poll)
    {
    	bool page_was_allocated;
    	struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
    			vma, addr, &page_was_allocated);
    
    	if (page_was_allocated)
    		swap_readpage(retpage, do_poll);
    
    	return retpage;
    }
    
    static unsigned int __swapin_nr_pages(unsigned long prev_offset,
    				      unsigned long offset,
    				      int hits,
    				      int max_pages,
    				      int prev_win)
    {
    	unsigned int pages, last_ra;
    
    	/*
    	 * This heuristic has been found to work well on both sequential and
    	 * random loads, swapping to hard disk or to SSD: please don't ask
    	 * what the "+ 2" means, it just happens to work well, that's all.
    	 */
    	pages = hits + 2;
    	if (pages == 2) {
    		/*
    		 * We can have no readahead hits to judge by: but must not get
    		 * stuck here forever, so check for an adjacent offset instead
    		 * (and don't even bother to check whether swap type is same).
    		 */
    		if (offset != prev_offset + 1 && offset != prev_offset - 1)
    			pages = 1;
    	} else {
    		unsigned int roundup = 4;
    		while (roundup < pages)
    			roundup <<= 1;
    		pages = roundup;
    	}
    
    	if (pages > max_pages)
    		pages = max_pages;
    
    	/* Don't shrink readahead too fast */
    	last_ra = prev_win / 2;
    	if (pages < last_ra)
    		pages = last_ra;
    
    	return pages;
    }
    
    static unsigned long swapin_nr_pages(unsigned long offset)
    {
    	static unsigned long prev_offset;
    	unsigned int hits, pages, max_pages;
    	static atomic_t last_readahead_pages;
    
    	max_pages = 1 << READ_ONCE(page_cluster);
    	if (max_pages <= 1)
    		return 1;
    
    	hits = atomic_xchg(&swapin_readahead_hits, 0);
    	pages = __swapin_nr_pages(prev_offset, offset, hits, max_pages,
    				  atomic_read(&last_readahead_pages));
    	if (!hits)
    		prev_offset = offset;
    	atomic_set(&last_readahead_pages, pages);
    
    	return pages;
    }
    
    /**
     * swap_cluster_readahead - swap in pages in hope we need them soon
     * @entry: swap entry of this memory
     * @gfp_mask: memory allocation flags
     * @vmf: fault information
     *
     * Returns the struct page for entry and addr, after queueing swapin.
     *
     * Primitive swap readahead code. We simply read an aligned block of
     * (1 << page_cluster) entries in the swap area. This method is chosen
     * because it doesn't cost us any seek time.  We also make sure to queue
     * the 'original' request together with the readahead ones...
     *
     * This has been extended to use the NUMA policies from the mm triggering
     * the readahead.
     *
     * Caller must hold read mmap_sem if vmf->vma is not NULL.
     */
    struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
    				struct vm_fault *vmf)
    {
    	struct page *page;
    	unsigned long entry_offset = swp_offset(entry);
    	unsigned long offset = entry_offset;
    	unsigned long start_offset, end_offset;
    	unsigned long mask;
    	struct swap_info_struct *si = swp_swap_info(entry);
    	struct blk_plug plug;
    	bool do_poll = true, page_allocated;
    	struct vm_area_struct *vma = vmf->vma;
    	unsigned long addr = vmf->address;
    
    	mask = swapin_nr_pages(offset) - 1;
    	if (!mask)
    		goto skip;
    
    	/* Test swap type to make sure the dereference is safe */
    	if (likely(si->flags & (SWP_BLKDEV | SWP_FS))) {
    		struct inode *inode = si->swap_file->f_mapping->host;
    		if (inode_read_congested(inode))
    			goto skip;
    	}
    
    	do_poll = false;
    	/* Read a page_cluster sized and aligned cluster around offset. */
    	start_offset = offset & ~mask;
    	end_offset = offset | mask;
    	if (!start_offset)	/* First page is swap header. */
    		start_offset++;
    	if (end_offset >= si->max)
    		end_offset = si->max - 1;
    
    	blk_start_plug(&plug);
    	for (offset = start_offset; offset <= end_offset ; offset++) {
    		/* Ok, do the async read-ahead now */
    		page = __read_swap_cache_async(
    			swp_entry(swp_type(entry), offset),
    			gfp_mask, vma, addr, &page_allocated);
    		if (!page)
    			continue;
    		if (page_allocated) {
    			swap_readpage(page, false);
    			if (offset != entry_offset) {
    				SetPageReadahead(page);
    				count_vm_event(SWAP_RA);
    			}
    		}
    		put_page(page);
    	}
    	blk_finish_plug(&plug);
    
    	lru_add_drain();	/* Push any new pages onto the LRU now */
    skip:
    	return read_swap_cache_async(entry, gfp_mask, vma, addr, do_poll);
    }
    
    int init_swap_address_space(unsigned int type, unsigned long nr_pages)
    {
    	struct address_space *spaces, *space;
    	unsigned int i, nr;
    
    	nr = DIV_ROUND_UP(nr_pages, SWAP_ADDRESS_SPACE_PAGES);
    	spaces = kvcalloc(nr, sizeof(struct address_space), GFP_KERNEL);
    	if (!spaces)
    		return -ENOMEM;
    	for (i = 0; i < nr; i++) {
    		space = spaces + i;
    		xa_init_flags(&space->i_pages, XA_FLAGS_LOCK_IRQ);
    		atomic_set(&space->i_mmap_writable, 0);
    		space->a_ops = &swap_aops;
    		/* swap cache doesn't use writeback related tags */
    		mapping_set_no_writeback_tags(space);
    	}
    	nr_swapper_spaces[type] = nr;
    	swapper_spaces[type] = spaces;
    
    	return 0;
    }
    
    void exit_swap_address_space(unsigned int type)
    {
    	kvfree(swapper_spaces[type]);
    	nr_swapper_spaces[type] = 0;
    	swapper_spaces[type] = NULL;
    }
    
    static inline void swap_ra_clamp_pfn(struct vm_area_struct *vma,
    				     unsigned long faddr,
    				     unsigned long lpfn,
    				     unsigned long rpfn,
    				     unsigned long *start,
    				     unsigned long *end)
    {
    	*start = max3(lpfn, PFN_DOWN(vma->vm_start),
    		      PFN_DOWN(faddr & PMD_MASK));
    	*end = min3(rpfn, PFN_DOWN(vma->vm_end),
    		    PFN_DOWN((faddr & PMD_MASK) + PMD_SIZE));
    }
    
    static void swap_ra_info(struct vm_fault *vmf,
    			struct vma_swap_readahead *ra_info)
    {
    	struct vm_area_struct *vma = vmf->vma;
    	unsigned long ra_val;
    	swp_entry_t entry;
    	unsigned long faddr, pfn, fpfn;
    	unsigned long start, end;
    	pte_t *pte, *orig_pte;
    	unsigned int max_win, hits, prev_win, win, left;
    #ifndef CONFIG_64BIT
    	pte_t *tpte;
    #endif
    
    	max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster),
    			     SWAP_RA_ORDER_CEILING);
    	if (max_win == 1) {
    		ra_info->win = 1;
    		return;
    	}
    
    	faddr = vmf->address;
    	orig_pte = pte = pte_offset_map(vmf->pmd, faddr);
    	entry = pte_to_swp_entry(*pte);
    	if ((unlikely(non_swap_entry(entry)))) {
    		pte_unmap(orig_pte);
    		return;
    	}
    
    	fpfn = PFN_DOWN(faddr);
    	ra_val = GET_SWAP_RA_VAL(vma);
    	pfn = PFN_DOWN(SWAP_RA_ADDR(ra_val));
    	prev_win = SWAP_RA_WIN(ra_val);
    	hits = SWAP_RA_HITS(ra_val);
    	ra_info->win = win = __swapin_nr_pages(pfn, fpfn, hits,
    					       max_win, prev_win);
    	atomic_long_set(&vma->swap_readahead_info,
    			SWAP_RA_VAL(faddr, win, 0));
    
    	if (win == 1) {
    		pte_unmap(orig_pte);
    		return;
    	}
    
    	/* Copy the PTEs because the page table may be unmapped */
    	if (fpfn == pfn + 1)
    		swap_ra_clamp_pfn(vma, faddr, fpfn, fpfn + win, &start, &end);
    	else if (pfn == fpfn + 1)
    		swap_ra_clamp_pfn(vma, faddr, fpfn - win + 1, fpfn + 1,
    				  &start, &end);
    	else {
    		left = (win - 1) / 2;
    		swap_ra_clamp_pfn(vma, faddr, fpfn - left, fpfn + win - left,
    				  &start, &end);
    	}
    	ra_info->nr_pte = end - start;
    	ra_info->offset = fpfn - start;
    	pte -= ra_info->offset;
    #ifdef CONFIG_64BIT
    	ra_info->ptes = pte;
    #else
    	tpte = ra_info->ptes;
    	for (pfn = start; pfn != end; pfn++)
    		*tpte++ = *pte++;
    #endif
    	pte_unmap(orig_pte);
    }
    
    /**
     * swap_vma_readahead - swap in pages in hope we need them soon
     * @entry: swap entry of this memory
     * @gfp_mask: memory allocation flags
     * @vmf: fault information
     *
     * Returns the struct page for entry and addr, after queueing swapin.
     *
     * Primitive swap readahead code. We simply read in a few pages whoes
     * virtual addresses are around the fault address in the same vma.
     *
     * Caller must hold read mmap_sem if vmf->vma is not NULL.
     *
     */
    static struct page *swap_vma_readahead(swp_entry_t fentry, gfp_t gfp_mask,
    				       struct vm_fault *vmf)
    {
    	struct blk_plug plug;
    	struct vm_area_struct *vma = vmf->vma;
    	struct page *page;
    	pte_t *pte, pentry;
    	swp_entry_t entry;
    	unsigned int i;
    	bool page_allocated;
    	struct vma_swap_readahead ra_info = {0,};
    
    	swap_ra_info(vmf, &ra_info);
    	if (ra_info.win == 1)
    		goto skip;
    
    	blk_start_plug(&plug);
    	for (i = 0, pte = ra_info.ptes; i < ra_info.nr_pte;
    	     i++, pte++) {
    		pentry = *pte;
    		if (pte_none(pentry))
    			continue;
    		if (pte_present(pentry))
    			continue;
    		entry = pte_to_swp_entry(pentry);
    		if (unlikely(non_swap_entry(entry)))
    			continue;
    		page = __read_swap_cache_async(entry, gfp_mask, vma,
    					       vmf->address, &page_allocated);
    		if (!page)
    			continue;
    		if (page_allocated) {
    			swap_readpage(page, false);
    			if (i != ra_info.offset) {
    				SetPageReadahead(page);
    				count_vm_event(SWAP_RA);
    			}
    		}
    		put_page(page);
    	}
    	blk_finish_plug(&plug);
    	lru_add_drain();
    skip:
    	return read_swap_cache_async(fentry, gfp_mask, vma, vmf->address,
    				     ra_info.win == 1);
    }
    
    /**
     * swapin_readahead - swap in pages in hope we need them soon
     * @entry: swap entry of this memory
     * @gfp_mask: memory allocation flags
     * @vmf: fault information
     *
     * Returns the struct page for entry and addr, after queueing swapin.
     *
     * It's a main entry function for swap readahead. By the configuration,
     * it will read ahead blocks by cluster-based(ie, physical disk based)
     * or vma-based(ie, virtual address based on faulty address) readahead.
     */
    struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
    				struct vm_fault *vmf)
    {
    	return swap_use_vma_readahead() ?
    			swap_vma_readahead(entry, gfp_mask, vmf) :
    			swap_cluster_readahead(entry, gfp_mask, vmf);
    }
    
    #ifdef CONFIG_SYSFS
    static ssize_t vma_ra_enabled_show(struct kobject *kobj,
    				     struct kobj_attribute *attr, char *buf)
    {
    	return sprintf(buf, "%s\n", enable_vma_readahead ? "true" : "false");
    }
    static ssize_t vma_ra_enabled_store(struct kobject *kobj,
    				      struct kobj_attribute *attr,
    				      const char *buf, size_t count)
    {
    	if (!strncmp(buf, "true", 4) || !strncmp(buf, "1", 1))
    		enable_vma_readahead = true;
    	else if (!strncmp(buf, "false", 5) || !strncmp(buf, "0", 1))
    		enable_vma_readahead = false;
    	else
    		return -EINVAL;
    
    	return count;
    }
    static struct kobj_attribute vma_ra_enabled_attr =
    	__ATTR(vma_ra_enabled, 0644, vma_ra_enabled_show,
    	       vma_ra_enabled_store);
    
    static struct attribute *swap_attrs[] = {
    	&vma_ra_enabled_attr.attr,
    	NULL,
    };
    
    static struct attribute_group swap_attr_group = {
    	.attrs = swap_attrs,
    };
    
    static int __init swap_init_sysfs(void)
    {
    	int err;
    	struct kobject *swap_kobj;
    
    	swap_kobj = kobject_create_and_add("swap", mm_kobj);
    	if (!swap_kobj) {
    		pr_err("failed to create swap kobject\n");
    		return -ENOMEM;
    	}
    	err = sysfs_create_group(swap_kobj, &swap_attr_group);
    	if (err) {
    		pr_err("failed to register swap group\n");
    		goto delete_obj;
    	}
    	return 0;
    
    delete_obj:
    	kobject_put(swap_kobj);
    	return err;
    }
    subsys_initcall(swap_init_sysfs);
    #endif