Re: [PATCH] vmscan: scan pages until it founds eligible pages

[Michal Hocko]

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.

> 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?

Anyway [1] has changed this behavior. Are you seeing the issue with this
patch dropped?

[1] http://www.ozlabs.org/~akpm/mmotm/broken-out/revert-mm-vmscan-account-for-skipped-pages-as-a-partial-scan.patch
-- 
Michal Hocko
SUSE Labs