diff options
author | Michel Lespinasse <walken@google.com> | 2010-10-26 21:21:57 (GMT) |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2010-10-26 23:52:09 (GMT) |
commit | d065bd810b6deb67d4897a14bfe21f8eb526ba99 (patch) | |
tree | f58c59075732ec4ccba336278c9bdc7ff61bef94 /arch/x86/mm | |
parent | b522c94da5d9cbc73f708be5e530ebc3bbd4a031 (diff) | |
download | linux-d065bd810b6deb67d4897a14bfe21f8eb526ba99.tar.xz |
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: 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>
Diffstat (limited to 'arch/x86/mm')
-rw-r--r-- | arch/x86/mm/fault.c | 38 |
1 files changed, 26 insertions, 12 deletions
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 852b319..9b2345c 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -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); |