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mm: retry page fault when blocking on disk transfer

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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: Michel Lespinasse <walken@google.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Reviewed-by: Wu 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: "H. Peter Anvin" <hpa@zytor.com>
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Michel Lespinasse
2010-10-26 14:21:57 -07:00
committed by Linus Torvalds
parent b522c94da5
commit d065bd810b
5 changed files with 64 additions and 15 deletions
Download Patch File Download Diff File Expand all files Collapse all files

38
arch/x86/mm/fault.c
View File

@@ -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 @@ good_area:
* 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);