From: Robin Dong Date: Mon, 8 Oct 2012 23:29:05 +0000 (-0700) Subject: mm: fix nonuniform page status when writing new file with small buffer X-Git-Tag: v3.7-rc1~74^2~142 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d741c9cdeee6a569dae0dbbaf028065402955b59;p=pandora-kernel.git 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 Reviewed-by: Minchan Kim Cc: KOSAKI Motohiro Reviewed-by: Johannes Weiner Cc: Wu Fengguang Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Reading git-diff-tree failed