For what it's worth, I tested this patch on my 3.4 kernel, and it works as advertised. Here's my setup. - 2 GB RAM - a 3 GB zram disk for swapping - start one "hog" process per second (each hog process mallocs and touches 200 MB of memory). - watch /proc/meminfo 1. I verified that the problem still exists on my current 3.4 kernel. With laptop_mode = 2, hog processes are oom-killed when about 1.8-1.9 (out of 3) GB of swap space are still left 2. I double-checked that the problem does not exist with laptop_mode = 0: hog processes are oom-killed when swap space is exhausted (with good approximation). 3. I added the two-line patch, put back laptop_mode = 2, and verified that hog processes are oom-killed when swap space is exhausted, same as case 2. Let me know if I can run any more tests for you, and thanks for all the support so far! On Wed, Jan 9, 2013 at 6:03 PM, Minchan Kim wrote: > Hi Andrew, > > On Wed, Jan 09, 2013 at 04:18:54PM -0800, Andrew Morton wrote: > > On Wed, 9 Jan 2013 15:21:13 +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. > > > > > > ... > > > > > > --- a/mm/vmscan.c > > > +++ b/mm/vmscan.c > > > @@ -780,6 +780,8 @@ static unsigned long shrink_page_list(struct > list_head *page_list, > > > if (PageAnon(page) && !PageSwapCache(page)) { > > > if (!(sc->gfp_mask & __GFP_IO)) > > > goto keep_locked; > > > + if (!sc->may_writepage) > > > + goto keep_locked; > > > if (!add_to_swap(page)) > > > goto activate_locked; > > > may_enter_fs = 1; > > > > I'm not really getting it, and the description is rather hard to follow > :( > > It seems I don't have a talent about description. :( > I hope it would be better this year. :) > > > > > We should be adding anon pages to swapcache even when laptop_mode is > > set. And we should be writing them to swap as well, then reclaiming > > them. The only thing laptop_mode shouild do is make the disk spin up > > less frequently - that doesn't mean "not at all"! > > So it seems your rationale is that let's save power in only system has > enough memory so let's remove may_writepage in reclaim path? > > If it is, I love it because I didn't see any number about power saving > through reclaiming throttling(But surely there was reason to add it) > and not sure it works well during long time because we have tweaked > reclaim part too many. > > > > > So something seems screwed up here and the patch looks like a > > heavy-handed workaround. Why aren't these anon pages getting written > > out in laptop_mode? > > Don't know. It was there long time and I don't want to screw it up. > If we decide paging out in reclaim path regardless of laptop_mode, > it makes the problem easy without ugly workaround. > > Remove may_writepage? If it's too agressive, we can remove it in only > direct reclaim path. > > > > > > > -- > > To unsubscribe, send a message with 'unsubscribe linux-mm' in > > the body to majordomo@kvack.org. For more info on Linux MM, > > see: http://www.linux-mm.org/ . > > Don't email: email@kvack.org > > -- > Kind regards, > Minchan Kim > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org >