On Wed, Jan 09, 2013 at 03:21:13PM +0900, Minchan Kim wrote: > Recently, Luigi reported there are lots of free swap space when > OOM happens. It's easily reproduced on zram-over-swap, where > many instance of memory hogs are running and laptop_mode is enabled. > > Luigi reported there was no problem when he disabled laptop_mode. > The problem when I investigate problem is following as. > > try_to_free_pages disable may_writepage if laptop_mode is enabled. > shrink_page_list adds lots of anon pages in swap cache by > add_to_swap, which makes pages Dirty and rotate them to head of > inactive LRU without pageout. If it is repeated, inactive anon LRU > is full of Dirty and SwapCache pages. > > In case of that, isolate_lru_pages fails because it try to isolate > clean page due to may_writepage == 0. > > The may_writepage could be 1 only if total_scanned is higher than > writeback_threshold in do_try_to_free_pages but unfortunately, > VM can't isolate anon pages from inactive anon lru list by > above reason and we already reclaimed all file-backed pages. > So it ends up OOM killing. > > This patch prevents to add a page to swap cache unnecessary when > may_writepage is unset so anoymous lru list isn't full of > Dirty/Swapcache page. So VM can isolate pages from anon lru list, > which ends up setting may_writepage to 1 and could swap out > anon lru pages. When OOM triggers, I confirmed swap space was full. > > Reported-by: Luigi Semenzato <semenzato@xxxxxxxxxx> > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> We used to ignore the page's writeback state on isolation in the past, could you include a reference to since when this problem has been in the tree? Also, would it make sense to tag it for one of the stable trees? -- 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>