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authorRobin Dong <sanbai@taobao.com>2012-10-08 16:29:05 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-10-09 16:22:19 +0900
commitd741c9cdeee6a569dae0dbbaf028065402955b59 (patch)
treeacdff4cf25911e5ba8294822bf2e8c74b4d67974 /mm
parent314e51b9851b4f4e8ab302243ff5a6fc6147f379 (diff)
mm: fix nonuniform page status when writing new file with small buffer
When writing a new file with 2048 bytes buffer, such as write(fd, buffer, 2048), it will call generic_perform_write() twice for every page: write_begin mark_page_accessed(page) write_end write_begin mark_page_accessed(page) write_end Pages 1-13 will be added to lru-pvecs in write_begin() and will *NOT* be added to active_list even they have be accessed twice because they are not PageLRU(page). But when page 14th comes, all pages in lru-pvecs will be moved to inactive_list (by __lru_cache_add() ) in first write_begin(), now page 14th *is* PageLRU(page). And after second write_end() only page 14th will be in active_list. In Hadoop environment, we do comes to this situation: after writing a file, we find out that only 14th, 28th, 42th... page are in active_list and others in inactive_list. Now kswapd works, shrinks the inactive_list, the file only have 14th, 28th...pages in memory, the readahead request size will be broken to only 52k (13*4k), system's performance falls dramatically. This problem can also replay by below steps (the machine has 8G memory): 1. dd if=/dev/zero of=/test/file.out bs=1024 count=1048576 2. cat another 7.5G file to /dev/null 3. vmtouch -m 1G -v /test/file.out, it will show: /test/file.out [oooooooooooooooooooOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO] 187847/262144 the 'o' means same pages are in memory but same are not. The solution for this problem is simple: the 14th page should be added to lru_add_pvecs before mark_page_accessed() just as other pages. [akpm@linux-foundation.org: tweak comment] [akpm@linux-foundation.org: grab better comment from the v3 patch] Signed-off-by: Robin Dong <sanbai@taobao.com> Reviewed-by: Minchan Kim <minchan@kernel.org> Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com> Reviewed-by: Johannes Weiner <hannes@cmpxchg.org> Cc: Wu Fengguang <fengguang.wu@intel.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/swap.c11
1 files changed, 10 insertions, 1 deletions
diff --git a/mm/swap.c b/mm/swap.c
index 77825883298f..f76c76c7501b 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -446,13 +446,22 @@ void mark_page_accessed(struct page *page)
}
EXPORT_SYMBOL(mark_page_accessed);
+/*
+ * Order of operations is important: flush the pagevec when it's already
+ * full, not when adding the last page, to make sure that last page is
+ * not added to the LRU directly when passed to this function. Because
+ * mark_page_accessed() (called after this when writing) only activates
+ * pages that are on the LRU, linear writes in subpage chunks would see
+ * every PAGEVEC_SIZE page activated, which is unexpected.
+ */
void __lru_cache_add(struct page *page, enum lru_list lru)
{
struct pagevec *pvec = &get_cpu_var(lru_add_pvecs)[lru];
page_cache_get(page);
- if (!pagevec_add(pvec, page))
+ if (!pagevec_space(pvec))
__pagevec_lru_add(pvec, lru);
+ pagevec_add(pvec, page);
put_cpu_var(lru_add_pvecs);
}
EXPORT_SYMBOL(__lru_cache_add);