Commit d065bd81 authored by Michel Lespinasse's avatar Michel Lespinasse Committed by Linus Torvalds
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mm: retry page fault when blocking on disk transfer



This change reduces mmap_sem hold times that are caused by waiting for
disk transfers when accessing file mapped VMAs.

It introduces the VM_FAULT_ALLOW_RETRY flag, which indicates that the call
site wants mmap_sem to be released if blocking on a pending disk transfer.
In that case, filemap_fault() returns the VM_FAULT_RETRY status bit and
do_page_fault() will then re-acquire mmap_sem and retry the page fault.

It is expected that the retry will hit the same page which will now be
cached, and thus it will complete with a low mmap_sem hold time.

Tests:

- microbenchmark: thread A mmaps a large file and does random read accesses
  to the mmaped area - achieves about 55 iterations/s. Thread B does
  mmap/munmap in a loop at a separate location - achieves 55 iterations/s
  before, 15000 iterations/s after.

- We are seeing related effects in some applications in house, which show
  significant performance regressions when running without this change.

[akpm@linux-foundation.org: fix warning & crash]
Signed-off-by: default avatarMichel Lespinasse <walken@google.com>
Acked-by: default avatarRik van Riel <riel@redhat.com>
Acked-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Reviewed-by: default avatarWu Fengguang <fengguang.wu@intel.com>
Cc: Ying Han <yinghan@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Acked-by: default avatar"H. Peter Anvin" <hpa@zytor.com>
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b522c94d
......@@ -956,8 +956,10 @@ do_page_fault(struct pt_regs *regs, unsigned long error_code)
struct task_struct *tsk;
unsigned long address;
struct mm_struct *mm;
int write;
int fault;
int write = error_code & PF_WRITE;
unsigned int flags = FAULT_FLAG_ALLOW_RETRY |
(write ? FAULT_FLAG_WRITE : 0);
tsk = current;
mm = tsk->mm;
......@@ -1068,6 +1070,7 @@ do_page_fault(struct pt_regs *regs, unsigned long error_code)
bad_area_nosemaphore(regs, error_code, address);
return;
}
retry:
down_read(&mm->mmap_sem);
} else {
/*
......@@ -1111,8 +1114,6 @@ do_page_fault(struct pt_regs *regs, unsigned long error_code)
* we can handle it..
*/
good_area:
write = error_code & PF_WRITE;
if (unlikely(access_error(error_code, write, vma))) {
bad_area_access_error(regs, error_code, address);
return;
......@@ -1123,21 +1124,34 @@ do_page_fault(struct pt_regs *regs, unsigned long error_code)
* make sure we exit gracefully rather than endlessly redo
* the fault:
*/
fault = handle_mm_fault(mm, vma, address, write ? FAULT_FLAG_WRITE : 0);
fault = handle_mm_fault(mm, vma, address, flags);
if (unlikely(fault & VM_FAULT_ERROR)) {
mm_fault_error(regs, error_code, address, fault);
return;
}
if (fault & VM_FAULT_MAJOR) {
tsk->maj_flt++;
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, 0,
regs, address);
} else {
tsk->min_flt++;
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, 0,
regs, address);
/*
* Major/minor page fault accounting is only done on the
* initial attempt. If we go through a retry, it is extremely
* likely that the page will be found in page cache at that point.
*/
if (flags & FAULT_FLAG_ALLOW_RETRY) {
if (fault & VM_FAULT_MAJOR) {
tsk->maj_flt++;
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, 0,
regs, address);
} else {
tsk->min_flt++;
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, 0,
regs, address);
}
if (fault & VM_FAULT_RETRY) {
/* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
* of starvation. */
flags &= ~FAULT_FLAG_ALLOW_RETRY;
goto retry;
}
}
check_v8086_mode(regs, address, tsk);
......
......@@ -144,6 +144,7 @@ extern pgprot_t protection_map[16];
#define FAULT_FLAG_WRITE 0x01 /* Fault was a write access */
#define FAULT_FLAG_NONLINEAR 0x02 /* Fault was via a nonlinear mapping */
#define FAULT_FLAG_MKWRITE 0x04 /* Fault was mkwrite of existing pte */
#define FAULT_FLAG_ALLOW_RETRY 0x08 /* Retry fault if blocking */
/*
* This interface is used by x86 PAT code to identify a pfn mapping that is
......@@ -723,6 +724,7 @@ static inline int page_mapped(struct page *page)
#define VM_FAULT_NOPAGE 0x0100 /* ->fault installed the pte, not return page */
#define VM_FAULT_LOCKED 0x0200 /* ->fault locked the returned page */
#define VM_FAULT_RETRY 0x0400 /* ->fault blocked, must retry */
#define VM_FAULT_HWPOISON_LARGE_MASK 0xf000 /* encodes hpage index for large hwpoison */
......
......@@ -299,6 +299,8 @@ static inline pgoff_t linear_page_index(struct vm_area_struct *vma,
extern void __lock_page(struct page *page);
extern int __lock_page_killable(struct page *page);
extern void __lock_page_nosync(struct page *page);
extern int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
unsigned int flags);
extern void unlock_page(struct page *page);
static inline void __set_page_locked(struct page *page)
......@@ -350,6 +352,17 @@ static inline void lock_page_nosync(struct page *page)
__lock_page_nosync(page);
}
/*
* lock_page_or_retry - Lock the page, unless this would block and the
* caller indicated that it can handle a retry.
*/
static inline int lock_page_or_retry(struct page *page, struct mm_struct *mm,
unsigned int flags)
{
might_sleep();
return trylock_page(page) || __lock_page_or_retry(page, mm, flags);
}
/*
* This is exported only for wait_on_page_locked/wait_on_page_writeback.
* Never use this directly!
......
......@@ -612,6 +612,19 @@ void __lock_page_nosync(struct page *page)
TASK_UNINTERRUPTIBLE);
}
int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
unsigned int flags)
{
if (!(flags & FAULT_FLAG_ALLOW_RETRY)) {
__lock_page(page);
return 1;
} else {
up_read(&mm->mmap_sem);
wait_on_page_locked(page);
return 0;
}
}
/**
* find_get_page - find and get a page reference
* @mapping: the address_space to search
......@@ -1550,7 +1563,8 @@ int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
goto no_cached_page;
}
lock_page(page);
if (!lock_page_or_retry(page, vma->vm_mm, vmf->flags))
return ret | VM_FAULT_RETRY;
/* Did it get truncated? */
if (unlikely(page->mapping != mapping)) {
......
......@@ -2627,6 +2627,7 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
struct page *page, *swapcache = NULL;
swp_entry_t entry;
pte_t pte;
int locked;
struct mem_cgroup *ptr = NULL;
int exclusive = 0;
int ret = 0;
......@@ -2677,8 +2678,12 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
goto out_release;
}
lock_page(page);
locked = lock_page_or_retry(page, mm, flags);
delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
if (!locked) {
ret |= VM_FAULT_RETRY;
goto out_release;
}
/*
* Make sure try_to_free_swap or reuse_swap_page or swapoff did not
......@@ -2927,7 +2932,8 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
vmf.page = NULL;
ret = vma->vm_ops->fault(vma, &vmf);
if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))
if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE |
VM_FAULT_RETRY)))
return ret;
if (unlikely(PageHWPoison(vmf.page))) {
......
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