From: Robin Dong <sanbai@xxxxxxxxxx> 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 The page 1~13th will be added to lru_add_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 will be moved from lru_add_pvecs to active_list (by __lru_cache_add() ) in first write_begin(), now page 14th *is* PageLRU(page) and after second write_end() it 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 kswaped 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 <sanbai@xxxxxxxxxx> --- mm/swap.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/swap.c b/mm/swap.c index 4e7e2ec..0874d44 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -399,8 +399,9 @@ 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); -- 1.7.9.5 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>