The patch titled page_fault retry with NOPAGE_RETRY has been removed from the -mm tree. Its filename was page_fault-retry-with-nopage_retry.patch This patch was dropped because it was nacked The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: page_fault retry with NOPAGE_RETRY From: Ying Han <yinghan@xxxxxxxxxx> Allow major faults to drop the mmap_sem read lock while waiting for synchronous disk read. This allows another thread which wishes to grab down_write(mmap_sem) to proceed while the current is waiting the disk IO. The patch extend the 'write' flag of handle_mm_fault() to FAULT_FLAG_RETRY as identify that the caller can tolerate the retry in the filemap_fault call patch. This patch helps a lot in cases we have writer which is waitting behind all readers, so it could execute much faster. I also made patches for all other arch. I am posting x86_64 here first and I will post others by the time everyone feels comfortable with this patch. [akpm@xxxxxxxxxxxxxxxxxxxx: untangle the `write' boolean from the FAULT_FLAG_foo non-boolean field] [akpm@xxxxxxxxxxxxxxxxxxxx: undo wrong spelling change] Signed-off-by: Mike Waychison <mikew@xxxxxxxxxx> Signed-off-by: Ying Han <yinghan@xxxxxxxxxx> Tested-by: Török Edwin <edwintorok@xxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Rohit Seth <rohitseth@xxxxxxxxxx> Cc: Hugh Dickins <hugh@xxxxxxxxxxx> Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: Lee Schermerhorn <lee.schermerhorn@xxxxxx> Cc: Nick Piggin <npiggin@xxxxxxx> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- arch/x86/mm/fault.c | 16 +++++++ include/linux/mm.h | 2 mm/filemap.c | 85 ++++++++++++++++++++++++++++++++++++++++-- mm/memory.c | 11 ++++- 4 files changed, 109 insertions(+), 5 deletions(-) diff -puN arch/x86/mm/fault.c~page_fault-retry-with-nopage_retry arch/x86/mm/fault.c --- a/arch/x86/mm/fault.c~page_fault-retry-with-nopage_retry +++ a/arch/x86/mm/fault.c @@ -977,6 +977,7 @@ do_page_fault(struct pt_regs *regs, unsi struct mm_struct *mm; int write; int fault; + int retry_flag = 1; tsk = current; mm = tsk->mm; @@ -1085,6 +1086,7 @@ do_page_fault(struct pt_regs *regs, unsi might_sleep(); } +retry: vma = find_vma(mm, address); if (unlikely(!vma)) { bad_area(regs, error_code, address); @@ -1137,6 +1139,20 @@ good_area: return; } + /* + * Here we retry fault once and switch to synchronous mode. The + * main reason is to prevent us from the cases of starvation. + * The retry logic open a starvation hole in which case pages might + * be removed or changed after the retry. + */ + if (fault & VM_FAULT_RETRY) { + if (retry_flag) { + retry_flag = 0; + goto retry; + } + BUG(); + } + if (fault & VM_FAULT_MAJOR) tsk->maj_flt++; else diff -puN include/linux/mm.h~page_fault-retry-with-nopage_retry include/linux/mm.h --- a/include/linux/mm.h~page_fault-retry-with-nopage_retry +++ a/include/linux/mm.h @@ -135,6 +135,7 @@ 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_RETRY 0x04 /* Retry major fault */ /* * This interface is used by x86 PAT code to identify a pfn mapping that is @@ -697,6 +698,7 @@ static inline int page_mapped(struct pag #define VM_FAULT_MINOR 0 /* For backwards compat. Remove me quickly. */ +#define VM_FAULT_RETRY 0x0010 #define VM_FAULT_OOM 0x0001 #define VM_FAULT_SIGBUS 0x0002 #define VM_FAULT_MAJOR 0x0004 diff -puN mm/filemap.c~page_fault-retry-with-nopage_retry mm/filemap.c --- a/mm/filemap.c~page_fault-retry-with-nopage_retry +++ a/mm/filemap.c @@ -714,6 +714,57 @@ repeat: EXPORT_SYMBOL(find_lock_page); /** + * find_lock_page_retry - locate, pin and lock a pagecache page + * @mapping: the address_space to search + * @offset: the page index + * @vma: vma in which the fault was taken + * @ppage: zero if page not present, otherwise point to the page in pagecache + * @retry: 1 indicate caller tolerate a retry. + * + * If retry flag is on, and page is already locked by someone else, return + * a hint of retry. + * + * Return *ppage==NULL if page is not in pagecache. Otherwise return *ppage + * points to the page in the pagecache with ret=VM_FAULT_RETRY indicate a + * hint to caller for retry, or ret=0 which means page is successfully locked. + */ +unsigned find_lock_page_retry(struct address_space *mapping, pgoff_t offset, + struct vm_area_struct *vma, struct page **ppage, + int retry) +{ + unsigned int ret = 0; + struct page *page; + +repeat: + page = find_get_page(mapping, offset); + if (page) { + if (!retry) + lock_page(page); + else { + if (!trylock_page(page)) { + struct mm_struct *mm = vma->vm_mm; + + up_read(&mm->mmap_sem); + wait_on_page_locked(page); + down_read(&mm->mmap_sem); + + page_cache_release(page); + return VM_FAULT_RETRY; + } + } + if (unlikely(page->mapping != mapping)) { + unlock_page(page); + page_cache_release(page); + goto repeat; + } + VM_BUG_ON(page->index != offset); + } + *ppage = page; + return ret; +} +EXPORT_SYMBOL(find_lock_page_retry); + +/** * find_or_create_page - locate or add a pagecache page * @mapping: the page's address_space * @index: the page's index into the mapping @@ -1459,6 +1510,8 @@ int filemap_fault(struct vm_area_struct pgoff_t size; int did_readaround = 0; int ret = 0; + int retry_flag = vmf->flags & FAULT_FLAG_RETRY; + int retry_ret; size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT; if (vmf->pgoff >= size) @@ -1473,6 +1526,8 @@ int filemap_fault(struct vm_area_struct */ retry_find: page = find_lock_page(mapping, vmf->pgoff); + +retry_find_nopage: /* * For sequential accesses, we use the generic readahead logic. */ @@ -1480,9 +1535,12 @@ retry_find: if (!page) { page_cache_sync_readahead(mapping, ra, file, vmf->pgoff, 1); - page = find_lock_page(mapping, vmf->pgoff); + retry_ret = find_lock_page_retry(mapping, vmf->pgoff, + vma, &page, retry_flag); if (!page) goto no_cached_page; + if (retry_ret == VM_FAULT_RETRY) + return retry_ret; } if (PageReadahead(page)) { page_cache_async_readahead(mapping, ra, file, page, @@ -1519,14 +1577,18 @@ retry_find: start = vmf->pgoff - ra_pages / 2; do_page_cache_readahead(mapping, file, start, ra_pages); } - page = find_lock_page(mapping, vmf->pgoff); + retry_ret = find_lock_page_retry(mapping, vmf->pgoff, + vma, &page, retry_flag); if (!page) goto no_cached_page; + if (retry_ret == VM_FAULT_RETRY) + return retry_ret; } if (!did_readaround) ra->mmap_miss--; +retry_page_update: /* * We have a locked page in the page cache, now we need to check * that it's up-to-date. If not, it is going to be due to an error. @@ -1561,8 +1623,23 @@ no_cached_page: * In the unlikely event that someone removed it in the * meantime, we'll just come back here and read it again. */ - if (error >= 0) - goto retry_find; + if (error >= 0) { + /* + * If caller cannot tolerate a retry in the ->fault path + * go back to check the page again. + */ + if (!retry_flag) + goto retry_find; + + retry_ret = find_lock_page_retry(mapping, vmf->pgoff, + vma, &page, retry_flag); + if (!page) + goto retry_find_nopage; + else if (retry_ret == VM_FAULT_RETRY) + return retry_ret; + else + goto retry_page_update; + } /* * An error return from page_cache_read can result if the diff -puN mm/memory.c~page_fault-retry-with-nopage_retry mm/memory.c --- a/mm/memory.c~page_fault-retry-with-nopage_retry +++ a/mm/memory.c @@ -2595,6 +2595,13 @@ static int __do_fault(struct mm_struct * vmf.page = NULL; ret = vma->vm_ops->fault(vma, &vmf); + + /* page may be available, but we have to restart the process + * because mmap_sem was dropped during the ->fault + */ + if (ret & VM_FAULT_RETRY) + return ret; + if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE))) return ret; @@ -2736,8 +2743,10 @@ static int do_linear_fault(struct mm_str { pgoff_t pgoff = (((address & PAGE_MASK) - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff; - unsigned int flags = (write_access ? FAULT_FLAG_WRITE : 0); + int write = write_access & ~FAULT_FLAG_RETRY; + unsigned int flags = (write ? FAULT_FLAG_WRITE : 0); + flags |= (write_access & FAULT_FLAG_RETRY); pte_unmap(page_table); return __do_fault(mm, vma, address, pmd, pgoff, flags, orig_pte); } _ Patches currently in -mm which might be from yinghan@xxxxxxxxxx are page_fault-retry-with-nopage_retry.patch proc-pid-maps-dont-show-pgoff-of-pure-anon-vmas.patch proc-pid-maps-dont-show-pgoff-of-pure-anon-vmas-checkpatch-fixes.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html