(6/6/12 7:39 AM), Robin Dong wrote: > 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); Please remove pagevec completely instead of insane hacking. -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>