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authorMel Gorman <mgorman@suse.de>2014-06-05 03:10:31 +0400
committerLinus Torvalds <torvalds@linux-foundation.org>2014-06-05 03:54:10 +0400
commit2457aec63745e235bcafb7ef312b182d8682f0fc (patch)
treec658266ed5a8c1acd4f2028c8bf69ab2a7c8ba42 /mm
parente7470ee89f003634a88e7b5e5a7b65b3025987de (diff)
downloadlinux-2457aec63745e235bcafb7ef312b182d8682f0fc.tar.xz
mm: non-atomically mark page accessed during page cache allocation where possible
aops->write_begin may allocate a new page and make it visible only to have mark_page_accessed called almost immediately after. Once the page is visible the atomic operations are necessary which is noticable overhead when writing to an in-memory filesystem like tmpfs but should also be noticable with fast storage. The objective of the patch is to initialse the accessed information with non-atomic operations before the page is visible. The bulk of filesystems directly or indirectly use grab_cache_page_write_begin or find_or_create_page for the initial allocation of a page cache page. This patch adds an init_page_accessed() helper which behaves like the first call to mark_page_accessed() but may called before the page is visible and can be done non-atomically. The primary APIs of concern in this care are the following and are used by most filesystems. find_get_page find_lock_page find_or_create_page grab_cache_page_nowait grab_cache_page_write_begin All of them are very similar in detail to the patch creates a core helper pagecache_get_page() which takes a flags parameter that affects its behavior such as whether the page should be marked accessed or not. Then old API is preserved but is basically a thin wrapper around this core function. Each of the filesystems are then updated to avoid calling mark_page_accessed when it is known that the VM interfaces have already done the job. There is a slight snag in that the timing of the mark_page_accessed() has now changed so in rare cases it's possible a page gets to the end of the LRU as PageReferenced where as previously it might have been repromoted. This is expected to be rare but it's worth the filesystem people thinking about it in case they see a problem with the timing change. It is also the case that some filesystems may be marking pages accessed that previously did not but it makes sense that filesystems have consistent behaviour in this regard. The test case used to evaulate this is a simple dd of a large file done multiple times with the file deleted on each iterations. The size of the file is 1/10th physical memory to avoid dirty page balancing. In the async case it will be possible that the workload completes without even hitting the disk and will have variable results but highlight the impact of mark_page_accessed for async IO. The sync results are expected to be more stable. The exception is tmpfs where the normal case is for the "IO" to not hit the disk. The test machine was single socket and UMA to avoid any scheduling or NUMA artifacts. Throughput and wall times are presented for sync IO, only wall times are shown for async as the granularity reported by dd and the variability is unsuitable for comparison. As async results were variable do to writback timings, I'm only reporting the maximum figures. The sync results were stable enough to make the mean and stddev uninteresting. The performance results are reported based on a run with no profiling. Profile data is based on a separate run with oprofile running. async dd 3.15.0-rc3 3.15.0-rc3 vanilla accessed-v2 ext3 Max elapsed 13.9900 ( 0.00%) 11.5900 ( 17.16%) tmpfs Max elapsed 0.5100 ( 0.00%) 0.4900 ( 3.92%) btrfs Max elapsed 12.8100 ( 0.00%) 12.7800 ( 0.23%) ext4 Max elapsed 18.6000 ( 0.00%) 13.3400 ( 28.28%) xfs Max elapsed 12.5600 ( 0.00%) 2.0900 ( 83.36%) The XFS figure is a bit strange as it managed to avoid a worst case by sheer luck but the average figures looked reasonable. samples percentage ext3 86107 0.9783 vmlinux-3.15.0-rc4-vanilla mark_page_accessed ext3 23833 0.2710 vmlinux-3.15.0-rc4-accessed-v3r25 mark_page_accessed ext3 5036 0.0573 vmlinux-3.15.0-rc4-accessed-v3r25 init_page_accessed ext4 64566 0.8961 vmlinux-3.15.0-rc4-vanilla mark_page_accessed ext4 5322 0.0713 vmlinux-3.15.0-rc4-accessed-v3r25 mark_page_accessed ext4 2869 0.0384 vmlinux-3.15.0-rc4-accessed-v3r25 init_page_accessed xfs 62126 1.7675 vmlinux-3.15.0-rc4-vanilla mark_page_accessed xfs 1904 0.0554 vmlinux-3.15.0-rc4-accessed-v3r25 init_page_accessed xfs 103 0.0030 vmlinux-3.15.0-rc4-accessed-v3r25 mark_page_accessed btrfs 10655 0.1338 vmlinux-3.15.0-rc4-vanilla mark_page_accessed btrfs 2020 0.0273 vmlinux-3.15.0-rc4-accessed-v3r25 init_page_accessed btrfs 587 0.0079 vmlinux-3.15.0-rc4-accessed-v3r25 mark_page_accessed tmpfs 59562 3.2628 vmlinux-3.15.0-rc4-vanilla mark_page_accessed tmpfs 1210 0.0696 vmlinux-3.15.0-rc4-accessed-v3r25 init_page_accessed tmpfs 94 0.0054 vmlinux-3.15.0-rc4-accessed-v3r25 mark_page_accessed [akpm@linux-foundation.org: don't run init_page_accessed() against an uninitialised pointer] Signed-off-by: Mel Gorman <mgorman@suse.de> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Jan Kara <jack@suse.cz> Cc: Michal Hocko <mhocko@suse.cz> Cc: Hugh Dickins <hughd@google.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Theodore Ts'o <tytso@mit.edu> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Rik van Riel <riel@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Tested-by: Prabhakar Lad <prabhakar.csengg@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/filemap.c202
-rw-r--r--mm/shmem.c6
-rw-r--r--mm/swap.c11
3 files changed, 91 insertions, 128 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index 47d235b357a7..0fcd792103f3 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -982,26 +982,6 @@ out:
EXPORT_SYMBOL(find_get_entry);
/**
- * find_get_page - find and get a page reference
- * @mapping: the address_space to search
- * @offset: the page index
- *
- * Looks up the page cache slot at @mapping & @offset. If there is a
- * page cache page, it is returned with an increased refcount.
- *
- * Otherwise, %NULL is returned.
- */
-struct page *find_get_page(struct address_space *mapping, pgoff_t offset)
-{
- struct page *page = find_get_entry(mapping, offset);
-
- if (radix_tree_exceptional_entry(page))
- page = NULL;
- return page;
-}
-EXPORT_SYMBOL(find_get_page);
-
-/**
* find_lock_entry - locate, pin and lock a page cache entry
* @mapping: the address_space to search
* @offset: the page cache index
@@ -1038,66 +1018,84 @@ repeat:
EXPORT_SYMBOL(find_lock_entry);
/**
- * find_lock_page - locate, pin and lock a pagecache page
+ * pagecache_get_page - find and get a page reference
* @mapping: the address_space to search
* @offset: the page index
+ * @fgp_flags: PCG flags
+ * @gfp_mask: gfp mask to use if a page is to be allocated
*
- * Looks up the page cache slot at @mapping & @offset. If there is a
- * page cache page, it is returned locked and with an increased
- * refcount.
- *
- * Otherwise, %NULL is returned.
- *
- * find_lock_page() may sleep.
- */
-struct page *find_lock_page(struct address_space *mapping, pgoff_t offset)
-{
- struct page *page = find_lock_entry(mapping, offset);
-
- if (radix_tree_exceptional_entry(page))
- page = NULL;
- return page;
-}
-EXPORT_SYMBOL(find_lock_page);
-
-/**
- * find_or_create_page - locate or add a pagecache page
- * @mapping: the page's address_space
- * @index: the page's index into the mapping
- * @gfp_mask: page allocation mode
+ * Looks up the page cache slot at @mapping & @offset.
*
- * Looks up the page cache slot at @mapping & @offset. If there is a
- * page cache page, it is returned locked and with an increased
- * refcount.
+ * PCG flags modify how the page is returned
*
- * If the page is not present, a new page is allocated using @gfp_mask
- * and added to the page cache and the VM's LRU list. The page is
- * returned locked and with an increased refcount.
+ * FGP_ACCESSED: the page will be marked accessed
+ * FGP_LOCK: Page is return locked
+ * FGP_CREAT: If page is not present then a new page is allocated using
+ * @gfp_mask and added to the page cache and the VM's LRU
+ * list. The page is returned locked and with an increased
+ * refcount. Otherwise, %NULL is returned.
*
- * On memory exhaustion, %NULL is returned.
+ * If FGP_LOCK or FGP_CREAT are specified then the function may sleep even
+ * if the GFP flags specified for FGP_CREAT are atomic.
*
- * find_or_create_page() may sleep, even if @gfp_flags specifies an
- * atomic allocation!
+ * If there is a page cache page, it is returned with an increased refcount.
*/
-struct page *find_or_create_page(struct address_space *mapping,
- pgoff_t index, gfp_t gfp_mask)
+struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
+ int fgp_flags, gfp_t cache_gfp_mask, gfp_t radix_gfp_mask)
{
struct page *page;
- int err;
+
repeat:
- page = find_lock_page(mapping, index);
- if (!page) {
- page = __page_cache_alloc(gfp_mask);
+ page = find_get_entry(mapping, offset);
+ if (radix_tree_exceptional_entry(page))
+ page = NULL;
+ if (!page)
+ goto no_page;
+
+ if (fgp_flags & FGP_LOCK) {
+ if (fgp_flags & FGP_NOWAIT) {
+ if (!trylock_page(page)) {
+ page_cache_release(page);
+ return NULL;
+ }
+ } else {
+ lock_page(page);
+ }
+
+ /* Has the page been truncated? */
+ if (unlikely(page->mapping != mapping)) {
+ unlock_page(page);
+ page_cache_release(page);
+ goto repeat;
+ }
+ VM_BUG_ON_PAGE(page->index != offset, page);
+ }
+
+ if (page && (fgp_flags & FGP_ACCESSED))
+ mark_page_accessed(page);
+
+no_page:
+ if (!page && (fgp_flags & FGP_CREAT)) {
+ int err;
+ if ((fgp_flags & FGP_WRITE) && mapping_cap_account_dirty(mapping))
+ cache_gfp_mask |= __GFP_WRITE;
+ if (fgp_flags & FGP_NOFS) {
+ cache_gfp_mask &= ~__GFP_FS;
+ radix_gfp_mask &= ~__GFP_FS;
+ }
+
+ page = __page_cache_alloc(cache_gfp_mask);
if (!page)
return NULL;
- /*
- * We want a regular kernel memory (not highmem or DMA etc)
- * allocation for the radix tree nodes, but we need to honour
- * the context-specific requirements the caller has asked for.
- * GFP_RECLAIM_MASK collects those requirements.
- */
- err = add_to_page_cache_lru(page, mapping, index,
- (gfp_mask & GFP_RECLAIM_MASK));
+
+ if (WARN_ON_ONCE(!(fgp_flags & FGP_LOCK)))
+ fgp_flags |= FGP_LOCK;
+
+ /* Init accessed so avoit atomic mark_page_accessed later */
+ if (fgp_flags & FGP_ACCESSED)
+ init_page_accessed(page);
+
+ err = add_to_page_cache_lru(page, mapping, offset, radix_gfp_mask);
if (unlikely(err)) {
page_cache_release(page);
page = NULL;
@@ -1105,9 +1103,10 @@ repeat:
goto repeat;
}
}
+
return page;
}
-EXPORT_SYMBOL(find_or_create_page);
+EXPORT_SYMBOL(pagecache_get_page);
/**
* find_get_entries - gang pagecache lookup
@@ -1404,39 +1403,6 @@ repeat:
}
EXPORT_SYMBOL(find_get_pages_tag);
-/**
- * grab_cache_page_nowait - returns locked page at given index in given cache
- * @mapping: target address_space
- * @index: the page index
- *
- * Same as grab_cache_page(), but do not wait if the page is unavailable.
- * This is intended for speculative data generators, where the data can
- * be regenerated if the page couldn't be grabbed. This routine should
- * be safe to call while holding the lock for another page.
- *
- * Clear __GFP_FS when allocating the page to avoid recursion into the fs
- * and deadlock against the caller's locked page.
- */
-struct page *
-grab_cache_page_nowait(struct address_space *mapping, pgoff_t index)
-{
- struct page *page = find_get_page(mapping, index);
-
- if (page) {
- if (trylock_page(page))
- return page;
- page_cache_release(page);
- return NULL;
- }
- page = __page_cache_alloc(mapping_gfp_mask(mapping) & ~__GFP_FS);
- if (page && add_to_page_cache_lru(page, mapping, index, GFP_NOFS)) {
- page_cache_release(page);
- page = NULL;
- }
- return page;
-}
-EXPORT_SYMBOL(grab_cache_page_nowait);
-
/*
* CD/DVDs are error prone. When a medium error occurs, the driver may fail
* a _large_ part of the i/o request. Imagine the worst scenario:
@@ -2406,7 +2372,6 @@ int pagecache_write_end(struct file *file, struct address_space *mapping,
{
const struct address_space_operations *aops = mapping->a_ops;
- mark_page_accessed(page);
return aops->write_end(file, mapping, pos, len, copied, page, fsdata);
}
EXPORT_SYMBOL(pagecache_write_end);
@@ -2488,34 +2453,18 @@ EXPORT_SYMBOL(generic_file_direct_write);
struct page *grab_cache_page_write_begin(struct address_space *mapping,
pgoff_t index, unsigned flags)
{
- int status;
- gfp_t gfp_mask;
struct page *page;
- gfp_t gfp_notmask = 0;
+ int fgp_flags = FGP_LOCK|FGP_ACCESSED|FGP_WRITE|FGP_CREAT;
- gfp_mask = mapping_gfp_mask(mapping);
- if (mapping_cap_account_dirty(mapping))
- gfp_mask |= __GFP_WRITE;
if (flags & AOP_FLAG_NOFS)
- gfp_notmask = __GFP_FS;
-repeat:
- page = find_lock_page(mapping, index);
+ fgp_flags |= FGP_NOFS;
+
+ page = pagecache_get_page(mapping, index, fgp_flags,
+ mapping_gfp_mask(mapping),
+ GFP_KERNEL);
if (page)
- goto found;
+ wait_for_stable_page(page);
- page = __page_cache_alloc(gfp_mask & ~gfp_notmask);
- if (!page)
- return NULL;
- status = add_to_page_cache_lru(page, mapping, index,
- GFP_KERNEL & ~gfp_notmask);
- if (unlikely(status)) {
- page_cache_release(page);
- if (status == -EEXIST)
- goto repeat;
- return NULL;
- }
-found:
- wait_for_stable_page(page);
return page;
}
EXPORT_SYMBOL(grab_cache_page_write_begin);
@@ -2564,7 +2513,7 @@ again:
status = a_ops->write_begin(file, mapping, pos, bytes, flags,
&page, &fsdata);
- if (unlikely(status))
+ if (unlikely(status < 0))
break;
if (mapping_writably_mapped(mapping))
@@ -2573,7 +2522,6 @@ again:
copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
flush_dcache_page(page);
- mark_page_accessed(page);
status = a_ops->write_end(file, mapping, pos, bytes, copied,
page, fsdata);
if (unlikely(status < 0))
diff --git a/mm/shmem.c b/mm/shmem.c
index f47fb38c4889..5402481c28d1 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1372,9 +1372,13 @@ shmem_write_begin(struct file *file, struct address_space *mapping,
loff_t pos, unsigned len, unsigned flags,
struct page **pagep, void **fsdata)
{
+ int ret;
struct inode *inode = mapping->host;
pgoff_t index = pos >> PAGE_CACHE_SHIFT;
- return shmem_getpage(inode, index, pagep, SGP_WRITE, NULL);
+ ret = shmem_getpage(inode, index, pagep, SGP_WRITE, NULL);
+ if (ret == 0 && *pagep)
+ init_page_accessed(*pagep);
+ return ret;
}
static int
diff --git a/mm/swap.c b/mm/swap.c
index 1fb25f8bb155..9e8e3472248b 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -614,6 +614,17 @@ void mark_page_accessed(struct page *page)
}
EXPORT_SYMBOL(mark_page_accessed);
+/*
+ * Used to mark_page_accessed(page) that is not visible yet and when it is
+ * still safe to use non-atomic ops
+ */
+void init_page_accessed(struct page *page)
+{
+ if (!PageReferenced(page))
+ __SetPageReferenced(page);
+}
+EXPORT_SYMBOL(init_page_accessed);
+
static void __lru_cache_add(struct page *page)
{
struct pagevec *pvec = &get_cpu_var(lru_add_pvec);