From 66fbaa13f444b6090a2bca2bce6e44479a779677 Mon Sep 17 00:00:00 2001 From: Robin Dong Date: Thu, 13 Sep 2012 10:58:30 +1000 Subject: [PATCH] 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. Signed-off-by: Robin Dong Reviewed-by: Minchan Kim Cc: KOSAKI Motohiro Reviewed-by: Johannes Weiner Cc: Wu Fengguang Signed-off-by: Andrew Morton --- mm/swap.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/mm/swap.c b/mm/swap.c index 77825883298f..692677cd0d95 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -446,13 +446,19 @@ void mark_page_accessed(struct page *page) } EXPORT_SYMBOL(mark_page_accessed); +/* + * Check pagevec space before adding new page into as + * it will prevent ununiform page status in + * mark_page_accessed() after __lru_cache_add() + */ 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); -- 2.39.5