From d065bd810b6deb67d4897a14bfe21f8eb526ba99 Mon Sep 17 00:00:00 2001 From: Michel Lespinasse Date: Tue, 26 Oct 2010 14:21:57 -0700 Subject: [PATCH] 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 Acked-by: Rik van Riel Acked-by: Linus Torvalds Cc: Nick Piggin Reviewed-by: Wu Fengguang Cc: Ying Han Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Thomas Gleixner Acked-by: "H. Peter Anvin" Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/x86/mm/fault.c | 38 ++++++++++++++++++++++++++------------ include/linux/mm.h | 2 ++ include/linux/pagemap.h | 13 +++++++++++++ mm/filemap.c | 16 +++++++++++++++- mm/memory.c | 10 ++++++++-- 5 files changed, 64 insertions(+), 15 deletions(-) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 852b319edbdc..9b2345c9e0c3 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); diff --git a/include/linux/mm.h b/include/linux/mm.h index 2862009f9573..3bf46655b50a 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -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 */ diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index e12cdc6d79ee..2d1ffe3cf1ee 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -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! diff --git a/mm/filemap.c b/mm/filemap.c index 8ed709a83eb7..33f81252a744 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -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 @@ retry_find: 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)) { diff --git a/mm/memory.c b/mm/memory.c index 92cc54e94137..714c4438d887 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -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))) {