On Wed, May 03, 2017 at 08:00:44AM +0200, Michal Hocko wrote: > On Wed 03-05-17 13:48:09, Minchan Kim wrote: > > On Tue, May 02, 2017 at 05:14:36PM +0200, Michal Hocko wrote: > > > On Tue 02-05-17 23:51:50, Minchan Kim wrote: > > > > Hi Michal, > > > > > > > > On Tue, May 02, 2017 at 09:54:32AM +0200, Michal Hocko wrote: > > > > > On Tue 02-05-17 14:14:52, Minchan Kim wrote: > > > > > > Oops, forgot to add lkml and linux-mm. > > > > > > Sorry for that. > > > > > > Send it again. > > > > > > > > > > > > >From 8ddf1c8aa15baf085bc6e8c62ce705459d57ea4c Mon Sep 17 00:00:00 2001 > > > > > > From: Minchan Kim <minchan@xxxxxxxxxx> > > > > > > Date: Tue, 2 May 2017 12:34:05 +0900 > > > > > > Subject: [PATCH] vmscan: scan pages until it founds eligible pages > > > > > > > > > > > > On Tue, May 02, 2017 at 01:40:38PM +0900, Minchan Kim wrote: > > > > > > There are premature OOM happening. Although there are a ton of free > > > > > > swap and anonymous LRU list of elgible zones, OOM happened. > > > > > > > > > > > > With investigation, skipping page of isolate_lru_pages makes reclaim > > > > > > void because it returns zero nr_taken easily so LRU shrinking is > > > > > > effectively nothing and just increases priority aggressively. > > > > > > Finally, OOM happens. > > > > > > > > > > I am not really sure I understand the problem you are facing. Could you > > > > > be more specific please? What is your configuration etc... > > > > > > > > Sure, KVM guest on x86_64, It has 2G memory and 1G swap and configured > > > > movablecore=1G to simulate highmem zone. > > > > Workload is a process consumes 2.2G memory and then random touch the > > > > address space so it makes lots of swap in/out. > > > > > > > > > > > > > > > balloon invoked oom-killer: gfp_mask=0x17080c0(GFP_KERNEL_ACCOUNT|__GFP_ZERO|__GFP_NOTRACK), nodemask=(null), order=0, oom_score_adj=0 > > > > > [...] > > > > > > Node 0 active_anon:1698864kB inactive_anon:261256kB active_file:208kB inactive_file:184kB unevictable:0kB isolated(anon):0kB isolated(file):0kB mapped:532kB dirty:108kB writeback:0kB shmem:172kB writeback_tmp:0kB unstable:0kB all_unreclaimable? no > > > > > > DMA free:7316kB min:32kB low:44kB high:56kB active_anon:8064kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:15992kB managed:15908kB mlocked:0kB slab_reclaimable:464kB slab_unreclaimable:40kB kernel_stack:0kB pagetables:24kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB > > > > > > lowmem_reserve[]: 0 992 992 1952 > > > > > > DMA32 free:9088kB min:2048kB low:3064kB high:4080kB active_anon:952176kB inactive_anon:0kB active_file:36kB inactive_file:0kB unevictable:0kB writepending:88kB present:1032192kB managed:1019388kB mlocked:0kB slab_reclaimable:13532kB slab_unreclaimable:16460kB kernel_stack:3552kB pagetables:6672kB bounce:0kB free_pcp:56kB local_pcp:24kB free_cma:0kB > > > > > > lowmem_reserve[]: 0 0 0 959 > > > > > > > > > > Hmm DMA32 has sufficient free memory to allow this order-0 request. > > > > > Inactive anon lru is basically empty. Why do not we rotate a really > > > > > large active anon list? Isn't this the primary problem? > > > > > > > > It's a side effect by skipping page logic in isolate_lru_pages > > > > I mentioned above in changelog. > > > > > > > > The problem is a lot of anonymous memory in movable zone(ie, highmem) > > > > and non-small memory in DMA32 zone. > > > > > > Such a configuration is questionable on its own. But let't keep this > > > part alone. > > > > It seems you are misunderstood. It's really common on 32bit. > > Yes, I am not arguing about 32b systems. It is quite common to see > issues which are inherent to the highmem zone. > > > Think of 2G DRAM system on 32bit. Normally, it's 1G normal:1G highmem. > > It's almost same with one I configured. > > > > > > > > > In heavy memory pressure, > > > > requesting a page in GFP_KERNEL triggers reclaim. VM knows inactive list > > > > is low so it tries to deactivate pages. For it, first of all, it tries > > > > to isolate pages from active list but there are lots of anonymous pages > > > > from movable zone so skipping logic in isolate_lru_pages works. With > > > > the result, isolate_lru_pages cannot isolate any eligible pages so > > > > reclaim trial is effectively void. It continues to meet OOM. > > > > > > But skipped pages should be rotated and we should eventually hit pages > > > from the right zone(s). Moreover we should scan the full LRU at priority > > > 0 so why exactly we hit the OOM killer? > > > > Yes, full scan in priority 0 but keep it in mind that the number of full > > LRU pages to scan is one of eligible pages, not all pages of the node. > > I have hard time understanding what you are trying to say here. > > > And isolate_lru_pages have accounted skipped pages as scan count so that > > VM cannot isolate any pages of eligible pages in LRU if non-eligible pages > > are a lot in the LRU. > > > > > > > > Anyway [1] has changed this behavior. Are you seeing the issue with this > > > patch dropped? > > > > Good point. Before the patch, it didn't increase scan count with skipped > > pages so with reverting [1], I guess it might work but worry about > > isolating lots of skipped pages into temporal pages_skipped list which > > might causes premate OOM. Anyway, I will test it when I returns at > > office after vacation. > > I do not think we want to drop this patch. I think we might be good > enough to simply fold this into the patch > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 24efcc20af91..ac146f10f222 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1472,7 +1472,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, > LIST_HEAD(pages_skipped); > > for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan && > - !list_empty(src); scan++) { > + !list_empty(src);) { > struct page *page; > > page = lru_to_page(src); > @@ -1486,6 +1486,12 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, > continue; > } > > + /* > + * Do not count skipped pages because we do want to isolate > + * some pages even when the LRU mostly contains ineligible > + * pages > + */ How about adding comment about "why"? /* * Do not count skipped pages because it makes the function to return with * none isolated pages if the LRU mostly contains inelgible pages so that * VM cannot reclaim any pages and trigger premature OOM. */ > + scan++; > switch (__isolate_lru_page(page, mode)) { > case 0: > nr_pages = hpage_nr_pages(page); Confirmed. It works as expected but it changed scan counter's behavior. How about this? diff --git a/mm/vmscan.c b/mm/vmscan.c index 2314aca47d12..846922d7942e 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1469,7 +1469,7 @@ static __always_inline void update_lru_sizes(struct lruvec *lruvec, * * Appropriate locks must be held before calling this function. * - * @nr_to_scan: The number of pages to look through on the list. + * @nr_to_scan: The number of eligible pages to look through on the list. * @lruvec: The LRU vector to pull pages from. * @dst: The temp list to put pages on to. * @nr_scanned: The number of pages that were scanned. @@ -1489,11 +1489,13 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 }; unsigned long nr_skipped[MAX_NR_ZONES] = { 0, }; unsigned long skipped = 0; - unsigned long scan, nr_pages; + unsigned long scan, total_scan, nr_pages; LIST_HEAD(pages_skipped); - for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan && - !list_empty(src); scan++) { + for (total_scan = scan = 0; scan < nr_to_scan && + nr_taken < nr_to_scan && + !list_empty(src); + total_scan++) { struct page *page; page = lru_to_page(src); @@ -1507,6 +1509,13 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, continue; } + /* + * Do not count skipped pages because it makes the function to + * return with none isolated pages if the LRU mostly contains + * inelgible pages so that VM cannot reclaim any pages and + * trigger premature OOM. + */ + scan++; switch (__isolate_lru_page(page, mode)) { case 0: nr_pages = hpage_nr_pages(page); @@ -1544,9 +1553,9 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, skipped += nr_skipped[zid]; } } - *nr_scanned = scan; + *nr_scanned = total_scan; trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan, - scan, skipped, nr_taken, mode, lru); + total_scan, skipped, nr_taken, mode, lru); update_lru_sizes(lruvec, lru, nr_zone_taken); return nr_taken; } -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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