Messages in this thread | | | Subject | Re: [[PATCH]] mm: khugepaged: recalculate min_free_kbytes after memory hotplug as expected by khugepaged | From | Vijay Balakrishna <> | Date | Thu, 17 Sep 2020 11:03:56 -0700 |
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On 9/17/2020 5:12 AM, Michal Hocko wrote: > On Wed 16-09-20 11:28:40, Vijay Balakrishna wrote: > [...] >> OOM splat below. I see we had kmem leak detection turned on here. We >> haven't run stress with kmem leak detection since uncovereing low >> min_free_kbytes. During investigation we wanted to make sure there is no >> kmem leaks, we didn't find significant leaks detected. >> >> [330319.766059] systemd invoked oom-killer: >> gfp_mask=0x40cc0(GFP_KERNEL|__GFP_COMP), order=1, oom_score_adj=0 > > [...] >> [330319.861064] Mem-Info: >> [330319.863519] active_anon:60744 inactive_anon:109226 isolated_anon:0 >> active_file:6418 inactive_file:3869 isolated_file:2 >> unevictable:0 dirty:8 writeback:1 unstable:0 >> slab_reclaimable:34660 slab_unreclaimable:795718 >> mapped:1256 shmem:165765 pagetables:689 bounce:0 >> free:340962 free_pcp:4672 free_cma:0 > > The memory consumption is predominantely in slab (unreclaimable). Only > ~8% of the memory is on LRUs (anonymous + file). Slab (both reclaimable > and unreclaimable) is ~40%. So there is still a lot of memory > unaccounted (direct users of the page allocator). This would partially > explain why the oom killer is not able to make progress and eventually > panics because it is the kernel which is blowing the memory consumption. > > There is still ~1G free memory but the problem is that this is a > GFP_KERNEL request which is not allowed to consume Movable memory. > Zone normal is depleted and therefore it cannot satisfy this request > even when there are some order-1 pages available. > >> [330319.928124] Node 0 Normal free:12652kB min:14344kB low:19092kB=20 >> high:23840kB active_anon:55340kB inactive_anon:60276kB active_file:60kB >> inactive_file:128kB unevictable:0kB writepending:4kB present:6220656kB >> managed:4750196kB mlocked:0kB kernel_stack:9568kB pagetables:2756kB >> bounce:0kB free_pcp:10056kB local_pcp:1376kB free_cma:0kB > [...] >> [330319.996879] Node 0 Normal: 3138*4kB (UME) 38*8kB (UM) 0*16kB 0*32kB >> 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 12856kB > > I do not see the state of swap in the oom splat so I assume you have > swap disabled. If that is the case then the memory reclaim cannot really > do much for this request. There is almost no page cache to reclaim.
No swap configured in our system. > > That being said I do not see how a increased min_free_kbytes could help > for this particular OOM situation. If there is really any relation it is > more of a unintended side effect.
I haven't had a chance to rerun stress with kmem leak detection to know if we still see OOM kills after min_free_kbytes restore. > > [...] >>>> Extreme values can damage your system. Setting min_free_kbytes to an >>>> extremely low value prevents the system from reclaiming memory, which can >>>> result in system hangs and OOM-killing processes. However, setting >>>> min_free_kbytes too high (for example, to 5–10% of total system memory) >>>> causes the system to enter an out-of-memory state immediately, resulting in >>>> the system spending too much time reclaiming memory. >>> >>> The auto tuned value should never reach such a low value to cause >>> problems. >> >> The auto tuned value is incorrect post hotplug memory operation, in our use >> case memoy hot add occurs very early during boot. > > Define incorrect. What are the actual values? Have you tried to increase > the value manually after the hotplug?
In our case SoC with 8GB memory, system tuned min_free_kbytes - first to 22528 - we perform memory hot add very early in boot - now min_free_kbytes is 8703
Before looking at code, first I manually restored min_free_kbytes soon after boot, reran stress and didn't notice symptoms I mentioned in change log.
Thanks, Vijay
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