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Message-ID: <20171101135855.bqg2kuj6ao2cicqi@dhcp22.suse.cz>
Date: Wed, 1 Nov 2017 14:58:55 +0100
From: Michal Hocko <mhocko@...nel.org>
To: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, David Rientjes <rientjes@...gle.com>,
Manish Jaggi <mjaggi@...iumnetworks.com>,
Oleg Nesterov <oleg@...hat.com>,
Vladimir Davydov <vdavydov@...tuozzo.com>
Subject: Re: [PATCH 2/2] mm,oom: Use ALLOC_OOM for OOM victim's last second
allocation.
On Wed 01-11-17 20:54:28, Tetsuo Handa wrote:
> Manish Jaggi noticed that running LTP oom01/oom02 ltp tests with high core
> count causes random kernel panics when an OOM victim which consumed memory
> in a way the OOM reaper does not help was selected by the OOM killer [1].
>
> ----------
> oom02 0 TINFO : start OOM testing for mlocked pages.
> oom02 0 TINFO : expected victim is 4578.
> oom02 0 TINFO : thread (ffff8b0e71f0), allocating 3221225472 bytes.
> oom02 0 TINFO : thread (ffff8b8e71f0), allocating 3221225472 bytes.
> (...snipped...)
> oom02 0 TINFO : thread (ffff8a0e71f0), allocating 3221225472 bytes.
> [ 364.737486] oom02:4583 invoked oom-killer: gfp_mask=0x16080c0(GFP_KERNEL|__GFP_ZERO|__GFP_NOTRACK), nodemask=1, order=0, oom_score_adj=0
> (...snipped...)
> [ 365.036127] [ pid ] uid tgid total_vm rss nr_ptes nr_pmds swapents oom_score_adj name
> [ 365.044691] [ 1905] 0 1905 3236 1714 10 4 0 0 systemd-journal
> [ 365.054172] [ 1908] 0 1908 20247 590 8 4 0 0 lvmetad
> [ 365.062959] [ 2421] 0 2421 3241 878 9 3 0 -1000 systemd-udevd
> [ 365.072266] [ 3125] 0 3125 3834 719 9 4 0 -1000 auditd
> [ 365.080963] [ 3145] 0 3145 1086 630 6 4 0 0 systemd-logind
> [ 365.090353] [ 3146] 0 3146 1208 596 7 3 0 0 irqbalance
> [ 365.099413] [ 3147] 81 3147 1118 625 5 4 0 -900 dbus-daemon
> [ 365.108548] [ 3149] 998 3149 116294 4180 26 5 0 0 polkitd
> [ 365.117333] [ 3164] 997 3164 19992 785 9 3 0 0 chronyd
> [ 365.126118] [ 3180] 0 3180 55605 7880 29 3 0 0 firewalld
> [ 365.135075] [ 3187] 0 3187 87842 3033 26 3 0 0 NetworkManager
> [ 365.144465] [ 3290] 0 3290 43037 1224 16 5 0 0 rsyslogd
> [ 365.153335] [ 3295] 0 3295 108279 6617 30 3 0 0 tuned
> [ 365.161944] [ 3308] 0 3308 27846 676 11 3 0 0 crond
> [ 365.170554] [ 3309] 0 3309 3332 616 10 3 0 -1000 sshd
> [ 365.179076] [ 3371] 0 3371 27307 364 6 3 0 0 agetty
> [ 365.187790] [ 3375] 0 3375 29397 1125 11 3 0 0 login
> [ 365.196402] [ 4178] 0 4178 4797 1119 14 4 0 0 master
> [ 365.205101] [ 4209] 89 4209 4823 1396 12 4 0 0 pickup
> [ 365.213798] [ 4211] 89 4211 4842 1485 12 3 0 0 qmgr
> [ 365.222325] [ 4491] 0 4491 27965 1022 8 3 0 0 bash
> [ 365.230849] [ 4513] 0 4513 670 365 5 3 0 0 oom02
> [ 365.239459] [ 4578] 0 4578 37776030 32890957 64257 138 0 0 oom02
> [ 365.248067] Out of memory: Kill process 4578 (oom02) score 952 or sacrifice child
> [ 365.255581] Killed process 4578 (oom02) total-vm:151104120kB, anon-rss:131562528kB, file-rss:1300kB, shmem-rss:0kB
> [ 365.266829] out_of_memory: Current (4583) has a pending SIGKILL
> [ 365.267347] oom_reaper: reaped process 4578 (oom02), now anon-rss:131559616kB, file-rss:0kB, shmem-rss:0kB
> [ 365.282658] oom_reaper: reaped process 4583 (oom02), now anon-rss:131561664kB, file-rss:0kB, shmem-rss:0kB
> [ 365.283361] oom02:4586 invoked oom-killer: gfp_mask=0x16040c0(GFP_KERNEL|__GFP_COMP|__GFP_NOTRACK), nodemask=1, order=0, oom_score_adj=0
> (...snipped...)
> [ 365.576164] oom02:4585 invoked oom-killer: gfp_mask=0x16080c0(GFP_KERNEL|__GFP_ZERO|__GFP_NOTRACK), nodemask=1, order=0, oom_score_adj=0
> (...snipped...)
> [ 365.576298] [ pid ] uid tgid total_vm rss nr_ptes nr_pmds swapents oom_score_adj name
> [ 365.576338] [ 2421] 0 2421 3241 878 9 3 0 -1000 systemd-udevd
> [ 365.576342] [ 3125] 0 3125 3834 719 9 4 0 -1000 auditd
> [ 365.576347] [ 3309] 0 3309 3332 616 10 3 0 -1000 sshd
> [ 365.576356] [ 4580] 0 4578 37776030 32890417 64258 138 0 0 oom02
> [ 365.576361] Kernel panic - not syncing: Out of memory and no killable processes...
> ----------
>
> Since commit 696453e66630ad45 ("mm, oom: task_will_free_mem should skip
> oom_reaped tasks") changed task_will_free_mem(current) in out_of_memory()
> to return false as soon as MMF_OOM_SKIP is set, many threads sharing the
> victim's mm were not able to try allocation from memory reserves after the
> OOM reaper gave up reclaiming memory.
>
> Until Linux 4.7, we were using
>
> if (current->mm &&
> (fatal_signal_pending(current) || task_will_free_mem(current)))
>
> as a condition to try allocation from memory reserves with the risk of OOM
> lockup, but reports like [1] were impossible. Linux 4.8+ are regressed
> compared to Linux 4.7 due to the risk of needlessly selecting more OOM
> victims.
So what you are essentially saying is that there is a race window
Proc1 Proc2 oom_reaper
__alloc_pages_slowpath out_of_memory
__gfp_pfmemalloc_flags select_bad_process # Proc1
[1] oom_reserves_allowed # false oom_kill_process
oom_reap_task
__alloc_pages_may_oom __oom_reap_task_mm
# doesn't unmap anything
set_bit(MMF_OOM_SKIP)
out_of_memory
task_will_free_mem
[2] MMF_OOM_SKIP check # true
select_bad_process # Another victim
mostly because the above is an artificial workload which triggers the
pathological path where nothing is really unmapped due to mlocked
memory, which makes the race window (1-2) smaller than it usually is. So
this is pretty much a corner case which we want to address by making
mlocked pages really reapable. Trying to use memory reserves for the
oom victims reduces changes of the race.
This would be really useful to have in the changelog IMHO.
> There is no need that the OOM victim is such malicious that consumes all
> memory. It is possible that a multithreaded but non memory hog process is
> selected by the OOM killer, and the OOM reaper fails to reclaim memory due
> to e.g. khugepaged [2], and the process fails to try allocation from memory
> reserves.
I am not sure about this part though. If the oom_reaper cannot take the
mmap_sem then it retries for 1s. Have you ever seen the race to be that
large?
> Therefore, this patch allows OOM victims to use ALLOC_OOM watermark
> for last second allocation attempt.
>
> [1] http://lkml.kernel.org/r/e6c83a26-1d59-4afd-55cf-04e58bdde188@caviumnetworks.com
> [2] http://lkml.kernel.org/r/201708090835.ICI69305.VFFOLMHOStJOQF@I-love.SAKURA.ne.jp
>
> Fixes: 696453e66630ad45 ("mm, oom: task_will_free_mem should skip oom_reaped tasks")
> Reported-by: Manish Jaggi <mjaggi@...iumnetworks.com>
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Vladimir Davydov <vdavydov@...tuozzo.com>
> Cc: David Rientjes <rientjes@...gle.com>
> ---
> mm/page_alloc.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 6654f52..382ed57 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4112,9 +4112,14 @@ struct page *alloc_pages_before_oomkill(const struct oom_control *oc)
> * we're still under heavy pressure. But make sure that this reclaim
> * attempt shall not depend on __GFP_DIRECT_RECLAIM && !__GFP_NORETRY
> * allocation which will never fail due to oom_lock already held.
> + * Also, make sure that OOM victims can try ALLOC_OOM watermark in case
> + * they haven't tried ALLOC_OOM watermark.
> */
> return get_page_from_freelist((oc->gfp_mask | __GFP_HARDWALL) &
> ~__GFP_DIRECT_RECLAIM, oc->order,
> + oom_reserves_allowed(current) &&
> + !(oc->gfp_mask & __GFP_NOMEMALLOC) ?
> + ALLOC_OOM :
> ALLOC_WMARK_HIGH|ALLOC_CPUSET, oc->ac);
This just makes my eyes bleed. Really, why don't you simply make this
more readable.
int alloc_flags = ALLOC_CPUSET | ALLOC_WMARK_HIGH;
gfp_t gfp_mask = oc->gfp_mask | __GFP_HARDWALL;
int reserves
gfp_mask &= ~__GFP_DIRECT_RECLAIM;
reserves = __gfp_pfmemalloc_flags(gfp_mask);
if (reserves)
alloc_flags = reserves;
> }
>
> --
> 1.8.3.1
--
Michal Hocko
SUSE Labs
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