The patch titled Subject: mm: fix nonuniform page status when writing new file with small buffer has been removed from the -mm tree. Its filename was mm-fix-nonuniform-page-status-when-writing-new-file-with-small-buffer.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Robin Dong <sanbai@xxxxxxxxxx> Subject: 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@xxxxxxxxxxxxxxxxxxxx: tweak comment] [akpm@xxxxxxxxxxxxxxxxxxxx: grab better comment from the v3 patch] Signed-off-by: Robin Dong <sanbai@xxxxxxxxxx> Reviewed-by: Minchan Kim <minchan@xxxxxxxxxx> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxx> Reviewed-by: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/swap.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff -puN mm/swap.c~mm-fix-nonuniform-page-status-when-writing-new-file-with-small-buffer mm/swap.c --- a/mm/swap.c~mm-fix-nonuniform-page-status-when-writing-new-file-with-small-buffer +++ a/mm/swap.c @@ -446,13 +446,22 @@ void mark_page_accessed(struct page *pag } 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); _ Patches currently in -mm which might be from sanbai@xxxxxxxxxx are origin.patch linux-next.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html