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Date: Wed, 2 Aug 2017 17:04:09 -0700
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] mm, oom: task_will_free_mem(current) should ignore
 MMF_OOM_SKIP for once.
Message-Id: <20170802170409.caaaab2a866cf8ac210291cc@linux-foundation.org>
In-Reply-To: <1501718104-8099-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
References: <1501718104-8099-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
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Sender: owner-linux-mm@kvack.org
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To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: linux-mm@kvack.org, David Rientjes <rientjes@google.com>, Manish Jaggi <mjaggi@caviumnetworks.com>, Michal Hocko <mhocko@suse.com>, Oleg Nesterov <oleg@redhat.com>, Vladimir Davydov <vdavydov@virtuozzo.com>

On Thu,  3 Aug 2017 08:55:04 +0900 Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> 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.
> 
> ...
>
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -652,6 +652,7 @@ struct task_struct {
>  	/* disallow userland-initiated cgroup migration */
>  	unsigned			no_cgroup_migration:1;
>  #endif
> +	unsigned			oom_kill_free_check_raced:1;
>  
>  	unsigned long			atomic_flags; /* Flags requiring atomic access. */
>  
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 9e8b4f0..a1ae78d 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -780,11 +780,19 @@ static bool task_will_free_mem(struct task_struct *task)
>  		return false;
>  
>  	/*
> -	 * This task has already been drained by the oom reaper so there are
> -	 * only small chances it will free some more
> +	 * It is possible that current thread fails to try allocation from
> +	 * memory reserves if the OOM reaper set MMF_OOM_SKIP on this mm before
> +	 * current thread calls out_of_memory() in order to get TIF_MEMDIE.
> +	 * In that case, allow current thread to try TIF_MEMDIE allocation
> +	 * before start selecting next OOM victims.
>  	 */
> -	if (test_bit(MMF_OOM_SKIP, &mm->flags))
> +	if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
> +		if (task == current && !task->oom_kill_free_check_raced) {
> +			task->oom_kill_free_check_raced = true;

OK, caller's task_lock() prevents races here.

nit: task->oom_kill_free_check_raced is `unsigned', so " = 1" would be
more truthful here...


> +			return true;
> +		}
>  		return false;
> +	}
>  
>  	if (atomic_read(&mm->mm_users) <= 1)
>  		return true;

--
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From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Subject: [PATCH] mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for once.
Date: Thu,  3 Aug 2017 08:55:04 +0900
Message-Id: <1501718104-8099-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: akpm@linux-foundation.org
Cc: linux-mm@kvack.org, Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>, David Rientjes <rientjes@google.com>, Manish Jaggi <mjaggi@caviumnetworks.com>, Michal Hocko <mhocko@suse.com>, Oleg Nesterov <oleg@redhat.com>, Vladimir Davydov <vdavydov@virtuozzo.com>

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.

----------
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.

We don't need to give up task_will_free_mem(current) without trying
allocation from memory reserves. We will need to select next OOM victim
only when allocation from memory reserves did not help.

Thus, this patch allows task_will_free_mem(current) to ignore MMF_OOM_SKIP
for once so that task_will_free_mem(current) will not start selecting next
OOM victim without trying allocation from memory reserves.

Link: http://lkml.kernel.org/r/e6c83a26-1d59-4afd-55cf-04e58bdde188@caviumnetworks.com
Reported-by: Manish Jaggi <mjaggi@caviumnetworks.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: David Rientjes <rientjes@google.com>
Fixes: 696453e66630ad45 ("mm, oom: task_will_free_mem should skip oom_reaped tasks")
---
 include/linux/sched.h |  1 +
 mm/oom_kill.c         | 14 +++++++++++---
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 94137e7..88da211 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -652,6 +652,7 @@ struct task_struct {
 	/* disallow userland-initiated cgroup migration */
 	unsigned			no_cgroup_migration:1;
 #endif
+	unsigned			oom_kill_free_check_raced:1;
 
 	unsigned long			atomic_flags; /* Flags requiring atomic access. */
 
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 9e8b4f0..a1ae78d 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -780,11 +780,19 @@ static bool task_will_free_mem(struct task_struct *task)
 		return false;
 
 	/*
-	 * This task has already been drained by the oom reaper so there are
-	 * only small chances it will free some more
+	 * It is possible that current thread fails to try allocation from
+	 * memory reserves if the OOM reaper set MMF_OOM_SKIP on this mm before
+	 * current thread calls out_of_memory() in order to get TIF_MEMDIE.
+	 * In that case, allow current thread to try TIF_MEMDIE allocation
+	 * before start selecting next OOM victims.
 	 */
-	if (test_bit(MMF_OOM_SKIP, &mm->flags))
+	if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
+		if (task == current && !task->oom_kill_free_check_raced) {
+			task->oom_kill_free_check_raced = true;
+			return true;
+		}
 		return false;
+	}
 
 	if (atomic_read(&mm->mm_users) <= 1)
 		return true;
-- 
1.8.3.1

--
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From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Thu, 3 Aug 2017 09:10:52 +0200
From: Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH] mm, oom: task_will_free_mem(current) should ignore
 MMF_OOM_SKIP for once.
Message-ID: <20170803071051.GB12521@dhcp22.suse.cz>
References: <1501718104-8099-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
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Content-Type: text/plain; charset=us-ascii
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In-Reply-To: <1501718104-8099-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org, David Rientjes <rientjes@google.com>, Manish Jaggi <mjaggi@caviumnetworks.com>, Oleg Nesterov <oleg@redhat.com>, Vladimir Davydov <vdavydov@virtuozzo.com>

On Thu 03-08-17 08:55:04, 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.
> 
> ----------
> 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.
> 
> We don't need to give up task_will_free_mem(current) without trying
> allocation from memory reserves. We will need to select next OOM victim
> only when allocation from memory reserves did not help.
> 
> Thus, this patch allows task_will_free_mem(current) to ignore MMF_OOM_SKIP
> for once so that task_will_free_mem(current) will not start selecting next
> OOM victim without trying allocation from memory reserves.

As I've already said this is an ugly hack and once we have
http://lkml.kernel.org/r/20170727090357.3205-2-mhocko@kernel.org merged
then it even shouldn't be needed because _all_ threads of the oom victim
will have an instant access to memory reserves.

So I do not think we want to merge this.

> Link: http://lkml.kernel.org/r/e6c83a26-1d59-4afd-55cf-04e58bdde188@caviumnetworks.com
> Reported-by: Manish Jaggi <mjaggi@caviumnetworks.com>
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
> Cc: David Rientjes <rientjes@google.com>
> Fixes: 696453e66630ad45 ("mm, oom: task_will_free_mem should skip oom_reaped tasks")
> ---
>  include/linux/sched.h |  1 +
>  mm/oom_kill.c         | 14 +++++++++++---
>  2 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 94137e7..88da211 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -652,6 +652,7 @@ struct task_struct {
>  	/* disallow userland-initiated cgroup migration */
>  	unsigned			no_cgroup_migration:1;
>  #endif
> +	unsigned			oom_kill_free_check_raced:1;
>  
>  	unsigned long			atomic_flags; /* Flags requiring atomic access. */
>  
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 9e8b4f0..a1ae78d 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -780,11 +780,19 @@ static bool task_will_free_mem(struct task_struct *task)
>  		return false;
>  
>  	/*
> -	 * This task has already been drained by the oom reaper so there are
> -	 * only small chances it will free some more
> +	 * It is possible that current thread fails to try allocation from
> +	 * memory reserves if the OOM reaper set MMF_OOM_SKIP on this mm before
> +	 * current thread calls out_of_memory() in order to get TIF_MEMDIE.
> +	 * In that case, allow current thread to try TIF_MEMDIE allocation
> +	 * before start selecting next OOM victims.
>  	 */
> -	if (test_bit(MMF_OOM_SKIP, &mm->flags))
> +	if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
> +		if (task == current && !task->oom_kill_free_check_raced) {
> +			task->oom_kill_free_check_raced = true;
> +			return true;
> +		}
>  		return false;
> +	}
>  
>  	if (atomic_read(&mm->mm_users) <= 1)
>  		return true;
> -- 
> 1.8.3.1
> 

-- 
Michal Hocko
SUSE Labs

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Subject: Re: [PATCH] mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for once.
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
References: <1501718104-8099-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
	<20170803071051.GB12521@dhcp22.suse.cz>
In-Reply-To: <20170803071051.GB12521@dhcp22.suse.cz>
Message-Id: <201708031653.JGD57352.OQFtVLSFOMOHJF@I-love.SAKURA.ne.jp>
Date: Thu, 3 Aug 2017 16:53:40 +0900
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Michal Hocko wrote:
> > We don't need to give up task_will_free_mem(current) without trying
> > allocation from memory reserves. We will need to select next OOM victim
> > only when allocation from memory reserves did not help.
> > 
> > Thus, this patch allows task_will_free_mem(current) to ignore MMF_OOM_SKIP
> > for once so that task_will_free_mem(current) will not start selecting next
> > OOM victim without trying allocation from memory reserves.
> 
> As I've already said this is an ugly hack and once we have
> http://lkml.kernel.org/r/20170727090357.3205-2-mhocko@kernel.org merged
> then it even shouldn't be needed because _all_ threads of the oom victim
> will have an instant access to memory reserves.
> 
> So I do not think we want to merge this.
> 

No, we still want to merge this, for 4.8+ kernels which won't get your patch
backported will need this. Even after your patch is merged, there is a race
window where allocating threads are between after gfp_pfmemalloc_allowed() and
before mutex_trylock(&oom_lock) in __alloc_pages_may_oom() which means that
some threads could call out_of_memory() and hit this task_will_free_mem(current)
test. Ignoring MMF_OOM_SKIP for once is still useful.

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Date: Thu, 3 Aug 2017 10:14:59 +0200
From: Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH] mm, oom: task_will_free_mem(current) should ignore
 MMF_OOM_SKIP for once.
Message-ID: <20170803081459.GD12521@dhcp22.suse.cz>
References: <1501718104-8099-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
 <20170803071051.GB12521@dhcp22.suse.cz>
 <201708031653.JGD57352.OQFtVLSFOMOHJF@I-love.SAKURA.ne.jp>
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To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org, rientjes@google.com, mjaggi@caviumnetworks.com, oleg@redhat.com, vdavydov@virtuozzo.com

On Thu 03-08-17 16:53:40, Tetsuo Handa wrote:
> Michal Hocko wrote:
> > > We don't need to give up task_will_free_mem(current) without trying
> > > allocation from memory reserves. We will need to select next OOM victim
> > > only when allocation from memory reserves did not help.
> > > 
> > > Thus, this patch allows task_will_free_mem(current) to ignore MMF_OOM_SKIP
> > > for once so that task_will_free_mem(current) will not start selecting next
> > > OOM victim without trying allocation from memory reserves.
> > 
> > As I've already said this is an ugly hack and once we have
> > http://lkml.kernel.org/r/20170727090357.3205-2-mhocko@kernel.org merged
> > then it even shouldn't be needed because _all_ threads of the oom victim
> > will have an instant access to memory reserves.
> > 
> > So I do not think we want to merge this.
> > 
> 
> No, we still want to merge this, for 4.8+ kernels which won't get your patch
> backported will need this. Even after your patch is merged, there is a race
> window where allocating threads are between after gfp_pfmemalloc_allowed() and
> before mutex_trylock(&oom_lock) in __alloc_pages_may_oom() which means that
> some threads could call out_of_memory() and hit this task_will_free_mem(current)
> test. Ignoring MMF_OOM_SKIP for once is still useful.

I disagree. I am _highly_ skeptical this is a stable material. The
mentioned test case is artificial and the source of the problem is
somewhere else. Moreover the culprit is somewhere else. It is in the oom
reaper setting MMF_OOM_SKIP too early and it should be addressed there.
Do not add workarounds where they are not appropriate.

-- 
Michal Hocko
SUSE Labs

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Subject: Re: [PATCH] mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for once.
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
References: <1501718104-8099-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
	<20170803071051.GB12521@dhcp22.suse.cz>
	<201708031653.JGD57352.OQFtVLSFOMOHJF@I-love.SAKURA.ne.jp>
	<20170803081459.GD12521@dhcp22.suse.cz>
In-Reply-To: <20170803081459.GD12521@dhcp22.suse.cz>
Message-Id: <201708042010.HDD60496.LFtOQMFJOSFHOV@I-love.SAKURA.ne.jp>
Date: Fri, 4 Aug 2017 20:10:09 +0900
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Michal Hocko wrote:
> On Thu 03-08-17 16:53:40, Tetsuo Handa wrote:
> > Michal Hocko wrote:
> > > > We don't need to give up task_will_free_mem(current) without trying
> > > > allocation from memory reserves. We will need to select next OOM victim
> > > > only when allocation from memory reserves did not help.
> > > > 
> > > > Thus, this patch allows task_will_free_mem(current) to ignore MMF_OOM_SKIP
> > > > for once so that task_will_free_mem(current) will not start selecting next
> > > > OOM victim without trying allocation from memory reserves.
> > > 
> > > As I've already said this is an ugly hack and once we have
> > > http://lkml.kernel.org/r/20170727090357.3205-2-mhocko@kernel.org merged
> > > then it even shouldn't be needed because _all_ threads of the oom victim
> > > will have an instant access to memory reserves.
> > > 
> > > So I do not think we want to merge this.
> > > 
> > 
> > No, we still want to merge this, for 4.8+ kernels which won't get your patch
> > backported will need this. Even after your patch is merged, there is a race
> > window where allocating threads are between after gfp_pfmemalloc_allowed() and
> > before mutex_trylock(&oom_lock) in __alloc_pages_may_oom() which means that
> > some threads could call out_of_memory() and hit this task_will_free_mem(current)
> > test. Ignoring MMF_OOM_SKIP for once is still useful.
> 
> I disagree. I am _highly_ skeptical this is a stable material. The
> mentioned test case is artificial and the source of the problem is
> somewhere else. Moreover the culprit is somewhere else. It is in the oom
> reaper setting MMF_OOM_SKIP too early and it should be addressed there.
> Do not add workarounds where they are not appropriate.
> 
So, what alternative can you provide us for now?

  The patch titled
       Subject: mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for once.
  has been removed from the -mm tree.  Its filename was
       mm-oom-task_will_free_memcurrent-should-ignore-mmf_oom_skip-for-once.patch

  This patch was dropped because an updated version will be merged

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From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Fri, 4 Aug 2017 13:26:00 +0200
From: Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH] mm, oom: task_will_free_mem(current) should ignore
 MMF_OOM_SKIP for once.
Message-ID: <20170804112600.GL26029@dhcp22.suse.cz>
References: <1501718104-8099-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
 <20170803071051.GB12521@dhcp22.suse.cz>
 <201708031653.JGD57352.OQFtVLSFOMOHJF@I-love.SAKURA.ne.jp>
 <20170803081459.GD12521@dhcp22.suse.cz>
 <201708042010.HDD60496.LFtOQMFJOSFHOV@I-love.SAKURA.ne.jp>
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To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org, rientjes@google.com, mjaggi@caviumnetworks.com, oleg@redhat.com, vdavydov.dev@gmail.com

On Fri 04-08-17 20:10:09, Tetsuo Handa wrote:
> Michal Hocko wrote:
> > On Thu 03-08-17 16:53:40, Tetsuo Handa wrote:
> > > Michal Hocko wrote:
> > > > > We don't need to give up task_will_free_mem(current) without trying
> > > > > allocation from memory reserves. We will need to select next OOM victim
> > > > > only when allocation from memory reserves did not help.
> > > > > 
> > > > > Thus, this patch allows task_will_free_mem(current) to ignore MMF_OOM_SKIP
> > > > > for once so that task_will_free_mem(current) will not start selecting next
> > > > > OOM victim without trying allocation from memory reserves.
> > > > 
> > > > As I've already said this is an ugly hack and once we have
> > > > http://lkml.kernel.org/r/20170727090357.3205-2-mhocko@kernel.org merged
> > > > then it even shouldn't be needed because _all_ threads of the oom victim
> > > > will have an instant access to memory reserves.
> > > > 
> > > > So I do not think we want to merge this.
> > > > 
> > > 
> > > No, we still want to merge this, for 4.8+ kernels which won't get your patch
> > > backported will need this. Even after your patch is merged, there is a race
> > > window where allocating threads are between after gfp_pfmemalloc_allowed() and
> > > before mutex_trylock(&oom_lock) in __alloc_pages_may_oom() which means that
> > > some threads could call out_of_memory() and hit this task_will_free_mem(current)
> > > test. Ignoring MMF_OOM_SKIP for once is still useful.
> > 
> > I disagree. I am _highly_ skeptical this is a stable material. The
> > mentioned test case is artificial and the source of the problem is
> > somewhere else. Moreover the culprit is somewhere else. It is in the oom
> > reaper setting MMF_OOM_SKIP too early and it should be addressed there.
> > Do not add workarounds where they are not appropriate.
> > 
> So, what alternative can you provide us for now?

As I've already said http://lkml.kernel.org/r/20170727090357.3205-2-mhocko@kernel.org
seems to be a better alternative. I am waiting for further review
feedback before reposting it again.

-- 
Michal Hocko
SUSE Labs

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Subject: Re: [PATCH] mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for once.
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
References: <20170803071051.GB12521@dhcp22.suse.cz>
	<201708031653.JGD57352.OQFtVLSFOMOHJF@I-love.SAKURA.ne.jp>
	<20170803081459.GD12521@dhcp22.suse.cz>
	<201708042010.HDD60496.LFtOQMFJOSFHOV@I-love.SAKURA.ne.jp>
	<20170804112600.GL26029@dhcp22.suse.cz>
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Cc: akpm@linux-foundation.org, linux-mm@kvack.org, rientjes@google.com, mjaggi@caviumnetworks.com, oleg@redhat.com, vdavydov.dev@gmail.com

Michal Hocko wrote:
> On Fri 04-08-17 20:10:09, Tetsuo Handa wrote:
> > Michal Hocko wrote:
> > > On Thu 03-08-17 16:53:40, Tetsuo Handa wrote:
> > > > Michal Hocko wrote:
> > > > > > We don't need to give up task_will_free_mem(current) without trying
> > > > > > allocation from memory reserves. We will need to select next OOM victim
> > > > > > only when allocation from memory reserves did not help.
> > > > > > 
> > > > > > Thus, this patch allows task_will_free_mem(current) to ignore MMF_OOM_SKIP
> > > > > > for once so that task_will_free_mem(current) will not start selecting next
> > > > > > OOM victim without trying allocation from memory reserves.
> > > > > 
> > > > > As I've already said this is an ugly hack and once we have
> > > > > http://lkml.kernel.org/r/20170727090357.3205-2-mhocko@kernel.org merged
> > > > > then it even shouldn't be needed because _all_ threads of the oom victim
> > > > > will have an instant access to memory reserves.
> > > > > 
> > > > > So I do not think we want to merge this.
> > > > > 
> > > > 
> > > > No, we still want to merge this, for 4.8+ kernels which won't get your patch
> > > > backported will need this. Even after your patch is merged, there is a race
> > > > window where allocating threads are between after gfp_pfmemalloc_allowed() and
> > > > before mutex_trylock(&oom_lock) in __alloc_pages_may_oom() which means that
> > > > some threads could call out_of_memory() and hit this task_will_free_mem(current)
> > > > test. Ignoring MMF_OOM_SKIP for once is still useful.
> > > 
> > > I disagree. I am _highly_ skeptical this is a stable material. The
> > > mentioned test case is artificial and the source of the problem is
> > > somewhere else. Moreover the culprit is somewhere else. It is in the oom
> > > reaper setting MMF_OOM_SKIP too early and it should be addressed there.
> > > Do not add workarounds where they are not appropriate.
> > > 
> > So, what alternative can you provide us for now?
> 
> As I've already said http://lkml.kernel.org/r/20170727090357.3205-2-mhocko@kernel.org
> seems to be a better alternative. I am waiting for further review
> feedback before reposting it again.
> 
As I've already said, your patch does not close this race completely.
Your patch will be too drastic/risky for stable material.

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Date: Fri, 4 Aug 2017 13:52:28 +0200
From: Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH] mm, oom: task_will_free_mem(current) should ignore
 MMF_OOM_SKIP for once.
Message-ID: <20170804115228.GO26029@dhcp22.suse.cz>
References: <20170803071051.GB12521@dhcp22.suse.cz>
 <201708031653.JGD57352.OQFtVLSFOMOHJF@I-love.SAKURA.ne.jp>
 <20170803081459.GD12521@dhcp22.suse.cz>
 <201708042010.HDD60496.LFtOQMFJOSFHOV@I-love.SAKURA.ne.jp>
 <20170804112600.GL26029@dhcp22.suse.cz>
 <201708042044.JDB64025.SOMOFOHJFFtQLV@I-love.SAKURA.ne.jp>
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To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org, rientjes@google.com, mjaggi@caviumnetworks.com, oleg@redhat.com, vdavydov.dev@gmail.com

On Fri 04-08-17 20:44:52, Tetsuo Handa wrote:
> Michal Hocko wrote:
> > On Fri 04-08-17 20:10:09, Tetsuo Handa wrote:
> > > Michal Hocko wrote:
> > > > On Thu 03-08-17 16:53:40, Tetsuo Handa wrote:
> > > > > Michal Hocko wrote:
> > > > > > > We don't need to give up task_will_free_mem(current) without trying
> > > > > > > allocation from memory reserves. We will need to select next OOM victim
> > > > > > > only when allocation from memory reserves did not help.
> > > > > > > 
> > > > > > > Thus, this patch allows task_will_free_mem(current) to ignore MMF_OOM_SKIP
> > > > > > > for once so that task_will_free_mem(current) will not start selecting next
> > > > > > > OOM victim without trying allocation from memory reserves.
> > > > > > 
> > > > > > As I've already said this is an ugly hack and once we have
> > > > > > http://lkml.kernel.org/r/20170727090357.3205-2-mhocko@kernel.org merged
> > > > > > then it even shouldn't be needed because _all_ threads of the oom victim
> > > > > > will have an instant access to memory reserves.
> > > > > > 
> > > > > > So I do not think we want to merge this.
> > > > > > 
> > > > > 
> > > > > No, we still want to merge this, for 4.8+ kernels which won't get your patch
> > > > > backported will need this. Even after your patch is merged, there is a race
> > > > > window where allocating threads are between after gfp_pfmemalloc_allowed() and
> > > > > before mutex_trylock(&oom_lock) in __alloc_pages_may_oom() which means that
> > > > > some threads could call out_of_memory() and hit this task_will_free_mem(current)
> > > > > test. Ignoring MMF_OOM_SKIP for once is still useful.
> > > > 
> > > > I disagree. I am _highly_ skeptical this is a stable material. The
> > > > mentioned test case is artificial and the source of the problem is
> > > > somewhere else. Moreover the culprit is somewhere else. It is in the oom
> > > > reaper setting MMF_OOM_SKIP too early and it should be addressed there.
> > > > Do not add workarounds where they are not appropriate.
> > > > 
> > > So, what alternative can you provide us for now?
> > 
> > As I've already said http://lkml.kernel.org/r/20170727090357.3205-2-mhocko@kernel.org
> > seems to be a better alternative. I am waiting for further review
> > feedback before reposting it again.
> > 
> As I've already said, your patch does not close this race completely.

Neither this patch.

> Your patch will be too drastic/risky for stable material.

As I've said this doesn't look like a stable material.
-- 
Michal Hocko
SUSE Labs

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Subject: Re: [PATCH] mm, oom: task_will_free_mem(current) should ignore
 MMF_OOM_SKIP for once.
References: <1501718104-8099-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
From: Manish Jaggi <mjaggi@caviumnetworks.com>
Message-ID: <a9a57062-a56d-4cc8-7027-6b80d12a8996@caviumnetworks.com>
Date: Fri, 4 Aug 2017 17:24:48 +0530
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To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>, akpm@linux-foundation.org
Cc: linux-mm@kvack.org, David Rientjes <rientjes@google.com>, Michal Hocko <mhocko@suse.com>, Oleg Nesterov <oleg@redhat.com>, Vladimir Davydov <vdavydov@virtuozzo.com>

Hi Tetsuo Handa,

On 8/3/2017 5:25 AM, 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.
>
> ----------
> 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...
> ----------
Wanted to understand the envisaged effect of this patch
- would this patch kill the task fully or it will still take few more 
iterations of oom-kill to kill other process to free memory
- when I apply this patch I see other tasks getting killed, though I 
didnt got panic in initial testing, I saw login process getting killed.
So I am not sure if this patch works...
> 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.
>
> We don't need to give up task_will_free_mem(current) without trying
> allocation from memory reserves. We will need to select next OOM victim
> only when allocation from memory reserves did not help.
>
> Thus, this patch allows task_will_free_mem(current) to ignore MMF_OOM_SKIP
> for once so that task_will_free_mem(current) will not start selecting next
> OOM victim without trying allocation from memory reserves.
>
> Link: http://lkml.kernel.org/r/e6c83a26-1d59-4afd-55cf-04e58bdde188@caviumnetworks.com
> Reported-by: Manish Jaggi <mjaggi@caviumnetworks.com>
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
> Cc: David Rientjes <rientjes@google.com>
> Fixes: 696453e66630ad45 ("mm, oom: task_will_free_mem should skip oom_reaped tasks")
> ---
>   include/linux/sched.h |  1 +
>   mm/oom_kill.c         | 14 +++++++++++---
>   2 files changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 94137e7..88da211 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -652,6 +652,7 @@ struct task_struct {
>   	/* disallow userland-initiated cgroup migration */
>   	unsigned			no_cgroup_migration:1;
>   #endif
> +	unsigned			oom_kill_free_check_raced:1;
>   
>   	unsigned long			atomic_flags; /* Flags requiring atomic access. */
>   
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 9e8b4f0..a1ae78d 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -780,11 +780,19 @@ static bool task_will_free_mem(struct task_struct *task)
>   		return false;
>   
>   	/*
> -	 * This task has already been drained by the oom reaper so there are
> -	 * only small chances it will free some more
> +	 * It is possible that current thread fails to try allocation from
> +	 * memory reserves if the OOM reaper set MMF_OOM_SKIP on this mm before
> +	 * current thread calls out_of_memory() in order to get TIF_MEMDIE.
> +	 * In that case, allow current thread to try TIF_MEMDIE allocation
> +	 * before start selecting next OOM victims.
>   	 */
> -	if (test_bit(MMF_OOM_SKIP, &mm->flags))
> +	if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
> +		if (task == current && !task->oom_kill_free_check_raced) {
> +			task->oom_kill_free_check_raced = true;
> +			return true;
> +		}
>   		return false;
> +	}
>   
>   	if (atomic_read(&mm->mm_users) <= 1)
>   		return true;

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From mboxrd@z Thu Jan  1 00:00:00 1970
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Subject: Re: [PATCH] mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for once.
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
References: <1501718104-8099-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
	<a9a57062-a56d-4cc8-7027-6b80d12a8996@caviumnetworks.com>
In-Reply-To: <a9a57062-a56d-4cc8-7027-6b80d12a8996@caviumnetworks.com>
Message-Id: <201708050024.ABD87010.SFFOVQOFOJMHtL@I-love.SAKURA.ne.jp>
Date: Sat, 5 Aug 2017 00:24:01 +0900
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To: mjaggi@caviumnetworks.com, akpm@linux-foundation.org
Cc: linux-mm@kvack.org, rientjes@google.com, mhocko@suse.com, oleg@redhat.com, vdavydov.dev@gmail.com

Manish Jaggi wrote:
> Hi Tetsuo Handa,
> 
> On 8/3/2017 5:25 AM, 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.
> >
> > ----------
> > 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...
> > ----------
> Wanted to understand the envisaged effect of this patch
> - would this patch kill the task fully or it will still take few more 
> iterations of oom-kill to kill other process to free memory
> - when I apply this patch I see other tasks getting killed, though I 
> didnt got panic in initial testing, I saw login process getting killed.
> So I am not sure if this patch works...

Thank you for testing. This patch is working as intended.

This patch (or any other patches) won't wait for the OOM victim (in this case
oom02) to be fully killed. We don't want to risk OOM lockup situation by waiting
for the OOM victim to be fully killed. If the OOM reaper kernel thread waits for
the OOM victim forever, different OOM stress will trigger OOM lockup situation.
Thus, the OOM reaper kernel thread gives up waiting for the OOM victim as soon as
memory which can be reclaimed before __mmput() from mmput() from exit_mm() from
do_exit() is called is reclaimed and sets MMF_OOM_SKIP.

Other tasks might be getting killed, for threads which task_will_free_mem(current)
returns false will call select_bad_process() and select_bad_process() will ignore
existing OOM victims with MMF_OOM_SKIP already set. Compared to older kernels
which do not have the OOM reaper support, this behavior looks like a regression.
But please be patient. This behavior is our choice for not to risk OOM lockup
situation.

This patch will prevent _all_ threads which task_will_free_mem(current) returns
true from calling select_bad_process(). And Michal's patch will prevent _most_
threads which task_will_free_mem(current) returns true from calling select_bad_process().
Since oom02 has many threads which task_will_free_mem(current) returns true,
this patch (or Michal's patch) will reduce possibility of killing all threads.

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From mboxrd@z Thu Jan  1 00:00:00 1970
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Subject: Re: [PATCH] mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for once.
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
References: <1501718104-8099-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
	<a9a57062-a56d-4cc8-7027-6b80d12a8996@caviumnetworks.com>
	<201708050024.ABD87010.SFFOVQOFOJMHtL@I-love.SAKURA.ne.jp>
In-Reply-To: <201708050024.ABD87010.SFFOVQOFOJMHtL@I-love.SAKURA.ne.jp>
Message-Id: <201708050054.FDD64564.tMQSVOFOFOLFJH@I-love.SAKURA.ne.jp>
Date: Sat, 5 Aug 2017 00:54:46 +0900
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Cc: linux-mm@kvack.org, rientjes@google.com, mhocko@suse.com, oleg@redhat.com, vdavydov.dev@gmail.com

Tetsuo Handa wrote:
> Manish Jaggi wrote:
> > Wanted to understand the envisaged effect of this patch
> > - would this patch kill the task fully or it will still take few more 
> > iterations of oom-kill to kill other process to free memory
> > - when I apply this patch I see other tasks getting killed, though I 
> > didnt got panic in initial testing, I saw login process getting killed.
> > So I am not sure if this patch works...
> 
> Thank you for testing. This patch is working as intended.
> 
> This patch (or any other patches) won't wait for the OOM victim (in this case
> oom02) to be fully killed. We don't want to risk OOM lockup situation by waiting
> for the OOM victim to be fully killed. If the OOM reaper kernel thread waits for
> the OOM victim forever, different OOM stress will trigger OOM lockup situation.
> Thus, the OOM reaper kernel thread gives up waiting for the OOM victim as soon as
> memory which can be reclaimed before __mmput() from mmput() from exit_mm() from
> do_exit() is called is reclaimed and sets MMF_OOM_SKIP.
> 
> Other tasks might be getting killed, for threads which task_will_free_mem(current)
> returns false will call select_bad_process() and select_bad_process() will ignore
> existing OOM victims with MMF_OOM_SKIP already set. Compared to older kernels
> which do not have the OOM reaper support, this behavior looks like a regression.
> But please be patient. This behavior is our choice for not to risk OOM lockup
> situation.
> 
> This patch will prevent _all_ threads which task_will_free_mem(current) returns
> true from calling select_bad_process(). And Michal's patch will prevent _most_
> threads which task_will_free_mem(current) returns true from calling select_bad_process().
> Since oom02 has many threads which task_will_free_mem(current) returns true,
> this patch (or Michal's patch) will reduce possibility of killing all threads.
> 

Oh, the last line was confusing.

Since oom02 has many threads which task_will_free_mem(current) returns true,
this patch (or Michal's patch) will reduce possibility of killing other tasks
(i.e. processes other than oom02) by increasing possibility of allocations by
OOM victim threads (i.e. threads in oom02) to succeed.

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From mboxrd@z Thu Jan  1 00:00:00 1970
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Subject: [PATCH v2] mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for once.
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
References: <1501718104-8099-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
In-Reply-To: <1501718104-8099-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
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Date: Sat, 19 Aug 2017 15:23:19 +0900
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Cc: linux-mm@kvack.org, rientjes@google.com, mjaggi@caviumnetworks.com, oleg@redhat.com, vdavydov@virtuozzo.com

Tetsuo Handa wrote at http://lkml.kernel.org/r/201708102328.ACD34352.OHFOLJMQVSFOFt@I-love.SAKURA.ne.jp :
> Michal Hocko wrote:
> > On Thu 10-08-17 21:10:30, Tetsuo Handa wrote:
> > > Michal Hocko wrote:
> > > > On Tue 08-08-17 11:14:50, Tetsuo Handa wrote:
> > > > > Michal Hocko wrote:
> > > > > > On Sat 05-08-17 10:02:55, Tetsuo Handa wrote:
> > > > > > > Michal Hocko wrote:
> > > > > > > > On Wed 26-07-17 20:33:21, Tetsuo Handa wrote:
> > > > > > > > > My question is, how can users know it if somebody was OOM-killed needlessly
> > > > > > > > > by allowing MMF_OOM_SKIP to race.
> > > > > > > > 
> > > > > > > > Is it really important to know that the race is due to MMF_OOM_SKIP?
> > > > > > > 
> > > > > > > Yes, it is really important. Needlessly selecting even one OOM victim is
> > > > > > > a pain which is difficult to explain to and persuade some of customers.
> > > > > > 
> > > > > > How is this any different from a race with a task exiting an releasing
> > > > > > some memory after we have crossed the point of no return and will kill
> > > > > > something?
> > > > > 
> > > > > I'm not complaining about an exiting task releasing some memory after we have
> > > > > crossed the point of no return.
> > > > > 
> > > > > What I'm saying is that we can postpone "the point of no return" if we ignore
> > > > > MMF_OOM_SKIP for once (both this "oom_reaper: close race without using oom_lock"
> > > > > thread and "mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for
> > > > > once." thread). These are race conditions we can avoid without crystal ball.
> > > > 
> > > > If those races are really that common than we can handle them even
> > > > without "try once more" tricks. Really this is just an ugly hack. If you
> > > > really care then make sure that we always try to allocate from memory
> > > > reserves before going down the oom path. In other words, try to find a
> > > > robust solution rather than tweaks around a problem.
> > > 
> > > Since your "mm, oom: allow oom reaper to race with exit_mmap" patch removes
> > > oom_lock serialization from the OOM reaper, possibility of calling out_of_memory()
> > > due to successful mutex_trylock(&oom_lock) would increase when the OOM reaper set
> > > MMF_OOM_SKIP quickly.
> > > 
> > > What if task_is_oom_victim(current) became true and MMF_OOM_SKIP was set
> > > on current->mm between after __gfp_pfmemalloc_flags() returned 0 and before
> > > out_of_memory() is called (due to successful mutex_trylock(&oom_lock)) ?
> > > 
> > > Excuse me? Are you suggesting to try memory reserves before
> > > task_is_oom_victim(current) becomes true?
> > 
> > No what I've tried to say is that if this really is a real problem,
> > which I am not sure about, then the proper way to handle that is to
> > attempt to allocate from memory reserves for an oom victim. I would be
> > even willing to take the oom_lock back into the oom reaper path if the
> > former turnes out to be awkward to implement. But all this assumes this
> > is a _real_ problem.
> 
> Aren't we back to square one? My question is, how can users know it if
> somebody was OOM-killed needlessly by allowing MMF_OOM_SKIP to race.
> 
> You don't want to call get_page_from_freelist() from out_of_memory(), do you?
> But without passing a flag "whether get_page_from_freelist() with memory reserves
> was already attempted if current thread is an OOM victim" to task_will_free_mem()
> in out_of_memory() and a flag "whether get_page_from_freelist() without memory
> reserves was already attempted if current thread is not an OOM victim" to
> test_bit(MMF_OOM_SKIP) in oom_evaluate_task(), we won't be able to know
> if somebody was OOM-killed needlessly by allowing MMF_OOM_SKIP to race.

Michal, I did not get your answer, and your "mm, oom: do not rely on
TIF_MEMDIE for memory reserves access" did not help solving this problem.
(I confirmed it by reverting your "mm, oom: allow oom reaper to race with
exit_mmap" and applying Andrea's "mm: oom: let oom_reap_task and exit_mmap
run concurrently" and this patch on top of linux-next-20170817.)

-----------
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sched.h>
#include <sys/mman.h>

#define NUMTHREADS 2
#define MMAPSIZE ((4096 * 1048576UL) / NUMTHREADS)
#define STACKSIZE 4096
static int pipe_fd[2] = { EOF, EOF };
static int memory_eater(void *unused)
{
	int fd = open("/dev/zero", O_RDONLY);
	char *buf = mmap(NULL, MMAPSIZE, PROT_WRITE | PROT_READ,
			 MAP_ANONYMOUS | MAP_SHARED, EOF, 0);
	read(pipe_fd[0], buf, 1);
	read(fd, buf, MMAPSIZE);
	pause();
	return 0;
}
int main(int argc, char *argv[])
{
	int i;
	char *stack;
	if (pipe(pipe_fd))
		return 1;
	stack = mmap(NULL, STACKSIZE * NUMTHREADS, PROT_WRITE | PROT_READ,
		     MAP_ANONYMOUS | MAP_SHARED, EOF, 0);
	for (i = 0; i < NUMTHREADS; i++)
		if (clone(memory_eater, stack + (i + 1) * STACKSIZE,
			  CLONE_THREAD | CLONE_SIGHAND | CLONE_VM | CLONE_FS |
			  CLONE_FILES, NULL) == -1)
			break;
	sleep(1);
	close(pipe_fd[1]);
	pause();
	return 0;
}
-----------

-----------
[  204.413605] Out of memory: Kill process 9286 (a.out) score 930 or sacrifice child
[  204.416241] Killed process 9286 (a.out) total-vm:4198476kB, anon-rss:72kB, file-rss:0kB, shmem-rss:3465520kB
[  204.419783] oom_reaper: reaped process 9286 (a.out), now anon-rss:0kB, file-rss:0kB, shmem-rss:3465720kB
[  204.455864] ------------[ cut here ]------------
[  204.457921] kernel BUG at mm/oom_kill.c:786!
[  204.459844] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC
[  204.461877] Modules linked in: coretemp pcspkr sg vmw_vmci i2c_piix4 shpchp sd_mod ata_generic pata_acpi serio_raw mptspi scsi_transport_spi mptscsih vmwgfx drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ahci ttm drm libahci ata_piix e1000 mptbase i2c_core libata ipv6
[  204.469328] CPU: 1 PID: 9287 Comm: a.out Not tainted 4.13.0-rc5-next-20170817+ #662
[  204.472117] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/02/2015
[  204.475265] task: ffff880135c88040 task.stack: ffff880137554000
[  204.477556] RIP: 0010:task_will_free_mem+0x1a7/0x240
[  204.479651] RSP: 0018:ffff880137557698 EFLAGS: 00010246
[  204.481750] RAX: 0000000000000000 RBX: ffff880135c88040 RCX: 00000000ffffffff
[  204.484344] RDX: ffff880135c88040 RSI: 0000000000000000 RDI: ffff880135c88040
[  204.487077] RBP: ffff8801375576b0 R08: 0000000000000000 R09: 0000000000000e6d
[  204.489565] R10: 0000000000000000 R11: 0000000000000e95 R12: ffff880133b48040
[  204.492019] R13: ffff88013f7fea20 R14: 0000000000000000 R15: 00000000014200ca
[  204.494467] FS:  00007fc4d067d740(0000) GS:ffff88013a000000(0000) knlGS:0000000000000000
[  204.497075] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  204.499231] CR2: 00007fc4b9ec2000 CR3: 0000000137b39004 CR4: 00000000001606e0
[  204.501907] Call Trace:
[  204.503426]  out_of_memory+0x54/0x560
[  204.505137]  __alloc_pages_nodemask+0xe91/0xf50
[  204.507002]  alloc_pages_vma+0x76/0x1a0
[  204.508694]  shmem_alloc_page+0x71/0xb0
[  204.510351]  ? native_sched_clock+0x36/0xa0
[  204.512059]  ? native_sched_clock+0x36/0xa0
[  204.513721]  ? find_get_entry+0x191/0x280
[  204.515327]  shmem_alloc_and_acct_page+0x83/0x230
[  204.517330]  shmem_getpage_gfp+0x1b6/0xe30
[  204.519005]  shmem_fault+0x97/0x200
[  204.520558]  ? __lock_acquire+0x4a7/0x1c20
[  204.522101]  ? __lock_acquire+0x4a7/0x1c20
[  204.523619]  __do_fault+0x19/0x120
[  204.524965]  __handle_mm_fault+0x8e3/0x1250
[  204.526484]  ? native_sched_clock+0x36/0xa0
[  204.527945]  handle_mm_fault+0x186/0x360
[  204.529355]  ? handle_mm_fault+0x47/0x360
[  204.530771]  __do_page_fault+0x1d2/0x510
[  204.532177]  do_page_fault+0x21/0x70
[  204.533563]  page_fault+0x22/0x30
[  204.534906] RIP: 0010:__clear_user+0x3d/0x70
[  204.536445] RSP: 0018:ffff880137557d58 EFLAGS: 00010206
[  204.538108] RAX: 0000000000000000 RBX: 0000000000000200 RCX: 0000000000000200
[  204.540173] RDX: 0000000000000000 RSI: 0000000000000008 RDI: 00007fc4b9ec2000
[  204.542215] RBP: ffff880137557d68 R08: 0000000000000001 R09: 0000000000000000
[  204.544263] R10: 0000000000000001 R11: 0000000000000001 R12: 00007fc4b9ec2000
[  204.546300] R13: ffff880137557e18 R14: 0000000069e16000 R15: 0000000000001000
[  204.548338]  ? __clear_user+0x1e/0x70
[  204.549679]  clear_user+0x34/0x50
[  204.551088]  iov_iter_zero+0x88/0x380
[  204.552403]  read_iter_zero+0x38/0xb0
[  204.553839]  new_sync_read+0xcc/0x110
[  204.555215]  __vfs_read+0x27/0x40
[  204.556605]  vfs_read+0xa0/0x160
[  204.557749]  SyS_read+0x53/0xc0
[  204.558907]  do_syscall_64+0x61/0x1d0
[  204.560197]  entry_SYSCALL64_slow_path+0x25/0x25
[  204.561628] RIP: 0033:0x7fc4d0194c30
[  204.562819] RSP: 002b:00007fc4d068afd8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[  204.564793] RAX: ffffffffffffffda RBX: 00007fc4500ac000 RCX: 00007fc4d0194c30
[  204.566802] RDX: 0000000080000000 RSI: 00007fc4500ac000 RDI: 0000000000000005
[  204.568760] RBP: 0000000000000005 R08: ffffffffffffffff R09: 0000000000000000
[  204.570641] R10: 00007fc4d068ad60 R11: 0000000000000246 R12: 00000000004006d9
[  204.572522] R13: 00007ffc72529cc0 R14: 0000000000000000 R15: 0000000000000000
[  204.574393] Code: 83 c4 08 89 d8 5b 41 5c 5d c3 65 48 8b 14 25 00 c6 00 00 31 c0 48 39 d3 0f 85 90 fe ff ff f6 83 78 16 00 00 02 0f 85 83 fe ff ff <0f> 0b 80 3d b6 f3 b5 00 00 0f 85 f7 fe ff ff e8 05 ec f8 ff 84 
[  204.579049] RIP: task_will_free_mem+0x1a7/0x240 RSP: ffff880137557698
[  204.580840] ---[ end trace 2be364e2657b83fa ]---
-----------

Therefore, I propose this patch for inclusion.

----------------------------------------

>>From cf6ef5a7b110d12e98bb2928e839abee16418188 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Thu, 17 Aug 2017 14:45:31 +0900
Subject: [PATCH v2] mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for once.

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. We don't need to give up task_will_free_mem(current) before trying
allocation from memory reserves. We will need to select next OOM victim
only when allocation from memory reserves did not help.

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.

Although "mm, oom: do not rely on TIF_MEMDIE for memory reserves access"
tried to reduce this race window by replacing TIF_MEMDIE with oom_mm, and
"mm: oom: let oom_reap_task and exit_mmap run concurrently" did not remove
oom_lock serialization, this race window is still easy to trigger. You can
confirm it by adding "BUG_ON(1);" at "task->oom_kill_free_check_raced = 1;"
of this patch.

Thus, this patch allows task_will_free_mem(current) to ignore MMF_OOM_SKIP
for once so that task_will_free_mem(current) will not start selecting next
OOM victim without trying allocation from memory reserves.

[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@caviumnetworks.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: David Rientjes <rientjes@google.com>
---
 include/linux/sched.h |  1 +
 mm/oom_kill.c         | 14 +++++++++++---
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 6110471..11f8d54 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -652,6 +652,7 @@ struct task_struct {
 	/* disallow userland-initiated cgroup migration */
 	unsigned			no_cgroup_migration:1;
 #endif
+	unsigned			oom_kill_free_check_raced:1;
 
 	unsigned long			atomic_flags; /* Flags requiring atomic access. */
 
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index ab8348d..c5fb8a3 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -749,11 +749,19 @@ static bool task_will_free_mem(struct task_struct *task)
 		return false;
 
 	/*
-	 * This task has already been drained by the oom reaper so there are
-	 * only small chances it will free some more
+	 * The current thread might fail to try OOM_ALLOC allocation if the OOM
+	 * reaper set MMF_OOM_SKIP on this mm when the current thread was
+	 * between after __gfp_pfmemalloc_flags() and before out_of_memory().
+	 * Make sure that the current thread has tried OOM_ALLOC allocation
+	 * before starting to select the next OOM victims.
 	 */
-	if (test_bit(MMF_OOM_SKIP, &mm->flags))
+	if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
+		if (task == current && !task->oom_kill_free_check_raced) {
+			task->oom_kill_free_check_raced = 1;
+			return true;
+		}
 		return false;
+	}
 
 	if (atomic_read(&mm->mm_users) <= 1)
 		return true;
-- 
2.9.5

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Date: Mon, 21 Aug 2017 10:43:07 +0200
From: Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH v2] mm, oom: task_will_free_mem(current) should ignore
 MMF_OOM_SKIP for once.
Message-ID: <20170821084307.GB25956@dhcp22.suse.cz>
References: <1501718104-8099-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
 <201708191523.BJH90621.MHOOFFQSOLJFtV@I-love.SAKURA.ne.jp>
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In-Reply-To: <201708191523.BJH90621.MHOOFFQSOLJFtV@I-love.SAKURA.ne.jp>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org, rientjes@google.com, mjaggi@caviumnetworks.com, oleg@redhat.com, vdavydov@virtuozzo.com

On Sat 19-08-17 15:23:19, Tetsuo Handa wrote:
> Tetsuo Handa wrote at http://lkml.kernel.org/r/201708102328.ACD34352.OHFOLJMQVSFOFt@I-love.SAKURA.ne.jp :
> > Michal Hocko wrote:
> > > On Thu 10-08-17 21:10:30, Tetsuo Handa wrote:
> > > > Michal Hocko wrote:
> > > > > On Tue 08-08-17 11:14:50, Tetsuo Handa wrote:
> > > > > > Michal Hocko wrote:
> > > > > > > On Sat 05-08-17 10:02:55, Tetsuo Handa wrote:
> > > > > > > > Michal Hocko wrote:
> > > > > > > > > On Wed 26-07-17 20:33:21, Tetsuo Handa wrote:
> > > > > > > > > > My question is, how can users know it if somebody was OOM-killed needlessly
> > > > > > > > > > by allowing MMF_OOM_SKIP to race.
> > > > > > > > > 
> > > > > > > > > Is it really important to know that the race is due to MMF_OOM_SKIP?
> > > > > > > > 
> > > > > > > > Yes, it is really important. Needlessly selecting even one OOM victim is
> > > > > > > > a pain which is difficult to explain to and persuade some of customers.
> > > > > > > 
> > > > > > > How is this any different from a race with a task exiting an releasing
> > > > > > > some memory after we have crossed the point of no return and will kill
> > > > > > > something?
> > > > > > 
> > > > > > I'm not complaining about an exiting task releasing some memory after we have
> > > > > > crossed the point of no return.
> > > > > > 
> > > > > > What I'm saying is that we can postpone "the point of no return" if we ignore
> > > > > > MMF_OOM_SKIP for once (both this "oom_reaper: close race without using oom_lock"
> > > > > > thread and "mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for
> > > > > > once." thread). These are race conditions we can avoid without crystal ball.
> > > > > 
> > > > > If those races are really that common than we can handle them even
> > > > > without "try once more" tricks. Really this is just an ugly hack. If you
> > > > > really care then make sure that we always try to allocate from memory
> > > > > reserves before going down the oom path. In other words, try to find a
> > > > > robust solution rather than tweaks around a problem.
> > > > 
> > > > Since your "mm, oom: allow oom reaper to race with exit_mmap" patch removes
> > > > oom_lock serialization from the OOM reaper, possibility of calling out_of_memory()
> > > > due to successful mutex_trylock(&oom_lock) would increase when the OOM reaper set
> > > > MMF_OOM_SKIP quickly.
> > > > 
> > > > What if task_is_oom_victim(current) became true and MMF_OOM_SKIP was set
> > > > on current->mm between after __gfp_pfmemalloc_flags() returned 0 and before
> > > > out_of_memory() is called (due to successful mutex_trylock(&oom_lock)) ?
> > > > 
> > > > Excuse me? Are you suggesting to try memory reserves before
> > > > task_is_oom_victim(current) becomes true?
> > > 
> > > No what I've tried to say is that if this really is a real problem,
> > > which I am not sure about, then the proper way to handle that is to
> > > attempt to allocate from memory reserves for an oom victim. I would be
> > > even willing to take the oom_lock back into the oom reaper path if the
> > > former turnes out to be awkward to implement. But all this assumes this
> > > is a _real_ problem.
> > 
> > Aren't we back to square one? My question is, how can users know it if
> > somebody was OOM-killed needlessly by allowing MMF_OOM_SKIP to race.
> > 
> > You don't want to call get_page_from_freelist() from out_of_memory(), do you?
> > But without passing a flag "whether get_page_from_freelist() with memory reserves
> > was already attempted if current thread is an OOM victim" to task_will_free_mem()
> > in out_of_memory() and a flag "whether get_page_from_freelist() without memory
> > reserves was already attempted if current thread is not an OOM victim" to
> > test_bit(MMF_OOM_SKIP) in oom_evaluate_task(), we won't be able to know
> > if somebody was OOM-killed needlessly by allowing MMF_OOM_SKIP to race.
> 
> Michal, I did not get your answer, and your "mm, oom: do not rely on
> TIF_MEMDIE for memory reserves access" did not help solving this problem.
> (I confirmed it by reverting your "mm, oom: allow oom reaper to race with
> exit_mmap" and applying Andrea's "mm: oom: let oom_reap_task and exit_mmap
> run concurrently" and this patch on top of linux-next-20170817.)

By "this patch" you probably mean a BUG_ON(tsk_is_oom_victim) somewhere
in task_will_free_mem right? I do not see anything like that in you
email.

> [  204.413605] Out of memory: Kill process 9286 (a.out) score 930 or sacrifice child
> [  204.416241] Killed process 9286 (a.out) total-vm:4198476kB, anon-rss:72kB, file-rss:0kB, shmem-rss:3465520kB
> [  204.419783] oom_reaper: reaped process 9286 (a.out), now anon-rss:0kB, file-rss:0kB, shmem-rss:3465720kB
> [  204.455864] ------------[ cut here ]------------
> [  204.457921] kernel BUG at mm/oom_kill.c:786!
> 
> Therefore, I propose this patch for inclusion.

i've already told you that this is a wrong approach to handle a possible
race and offered you an alternative. I realy fail to see why you keep
reposting it. So to make myself absolutely clear

Nacked-by: Michal Hocko <mhocko@suse.com> to the patch below.
 
> >From cf6ef5a7b110d12e98bb2928e839abee16418188 Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Date: Thu, 17 Aug 2017 14:45:31 +0900
> Subject: [PATCH v2] mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for once.
> 
> 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. We don't need to give up task_will_free_mem(current) before trying
> allocation from memory reserves. We will need to select next OOM victim
> only when allocation from memory reserves did not help.
> 
> 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.
> 
> Although "mm, oom: do not rely on TIF_MEMDIE for memory reserves access"
> tried to reduce this race window by replacing TIF_MEMDIE with oom_mm, and
> "mm: oom: let oom_reap_task and exit_mmap run concurrently" did not remove
> oom_lock serialization, this race window is still easy to trigger. You can
> confirm it by adding "BUG_ON(1);" at "task->oom_kill_free_check_raced = 1;"
> of this patch.
> 
> Thus, this patch allows task_will_free_mem(current) to ignore MMF_OOM_SKIP
> for once so that task_will_free_mem(current) will not start selecting next
> OOM victim without trying allocation from memory reserves.
> 
> [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@caviumnetworks.com>
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
> Cc: David Rientjes <rientjes@google.com>
> ---
>  include/linux/sched.h |  1 +
>  mm/oom_kill.c         | 14 +++++++++++---
>  2 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 6110471..11f8d54 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -652,6 +652,7 @@ struct task_struct {
>  	/* disallow userland-initiated cgroup migration */
>  	unsigned			no_cgroup_migration:1;
>  #endif
> +	unsigned			oom_kill_free_check_raced:1;
>  
>  	unsigned long			atomic_flags; /* Flags requiring atomic access. */
>  
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index ab8348d..c5fb8a3 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -749,11 +749,19 @@ static bool task_will_free_mem(struct task_struct *task)
>  		return false;
>  
>  	/*
> -	 * This task has already been drained by the oom reaper so there are
> -	 * only small chances it will free some more
> +	 * The current thread might fail to try OOM_ALLOC allocation if the OOM
> +	 * reaper set MMF_OOM_SKIP on this mm when the current thread was
> +	 * between after __gfp_pfmemalloc_flags() and before out_of_memory().
> +	 * Make sure that the current thread has tried OOM_ALLOC allocation
> +	 * before starting to select the next OOM victims.
>  	 */
> -	if (test_bit(MMF_OOM_SKIP, &mm->flags))
> +	if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
> +		if (task == current && !task->oom_kill_free_check_raced) {
> +			task->oom_kill_free_check_raced = 1;
> +			return true;
> +		}
>  		return false;
> +	}
>  
>  	if (atomic_read(&mm->mm_users) <= 1)
>  		return true;
> -- 
> 2.9.5

-- 
Michal Hocko
SUSE Labs

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Subject: Re: [PATCH v2] mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for once.
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
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Cc: akpm@linux-foundation.org, linux-mm@kvack.org, rientjes@google.com, mjaggi@caviumnetworks.com, oleg@redhat.com, vdavydov@virtuozzo.com

Michal Hocko wrote:
> On Sat 19-08-17 15:23:19, Tetsuo Handa wrote:
> > Tetsuo Handa wrote at http://lkml.kernel.org/r/201708102328.ACD34352.OHFOLJMQVSFOFt@I-love.SAKURA.ne.jp :
> > > Michal Hocko wrote:
> > > > On Thu 10-08-17 21:10:30, Tetsuo Handa wrote:
> > > > > Michal Hocko wrote:
> > > > > > On Tue 08-08-17 11:14:50, Tetsuo Handa wrote:
> > > > > > > Michal Hocko wrote:
> > > > > > > > On Sat 05-08-17 10:02:55, Tetsuo Handa wrote:
> > > > > > > > > Michal Hocko wrote:
> > > > > > > > > > On Wed 26-07-17 20:33:21, Tetsuo Handa wrote:
> > > > > > > > > > > My question is, how can users know it if somebody was OOM-killed needlessly
> > > > > > > > > > > by allowing MMF_OOM_SKIP to race.
> > > > > > > > > > 
> > > > > > > > > > Is it really important to know that the race is due to MMF_OOM_SKIP?
> > > > > > > > > 
> > > > > > > > > Yes, it is really important. Needlessly selecting even one OOM victim is
> > > > > > > > > a pain which is difficult to explain to and persuade some of customers.
> > > > > > > > 
> > > > > > > > How is this any different from a race with a task exiting an releasing
> > > > > > > > some memory after we have crossed the point of no return and will kill
> > > > > > > > something?
> > > > > > > 
> > > > > > > I'm not complaining about an exiting task releasing some memory after we have
> > > > > > > crossed the point of no return.
> > > > > > > 
> > > > > > > What I'm saying is that we can postpone "the point of no return" if we ignore
> > > > > > > MMF_OOM_SKIP for once (both this "oom_reaper: close race without using oom_lock"
> > > > > > > thread and "mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for
> > > > > > > once." thread). These are race conditions we can avoid without crystal ball.
> > > > > > 
> > > > > > If those races are really that common than we can handle them even
> > > > > > without "try once more" tricks. Really this is just an ugly hack. If you
> > > > > > really care then make sure that we always try to allocate from memory
> > > > > > reserves before going down the oom path. In other words, try to find a
> > > > > > robust solution rather than tweaks around a problem.
> > > > > 
> > > > > Since your "mm, oom: allow oom reaper to race with exit_mmap" patch removes
> > > > > oom_lock serialization from the OOM reaper, possibility of calling out_of_memory()
> > > > > due to successful mutex_trylock(&oom_lock) would increase when the OOM reaper set
> > > > > MMF_OOM_SKIP quickly.
> > > > > 
> > > > > What if task_is_oom_victim(current) became true and MMF_OOM_SKIP was set
> > > > > on current->mm between after __gfp_pfmemalloc_flags() returned 0 and before
> > > > > out_of_memory() is called (due to successful mutex_trylock(&oom_lock)) ?
> > > > > 
> > > > > Excuse me? Are you suggesting to try memory reserves before
> > > > > task_is_oom_victim(current) becomes true?
> > > > 
> > > > No what I've tried to say is that if this really is a real problem,
> > > > which I am not sure about, then the proper way to handle that is to
> > > > attempt to allocate from memory reserves for an oom victim. I would be
> > > > even willing to take the oom_lock back into the oom reaper path if the
> > > > former turnes out to be awkward to implement. But all this assumes this
> > > > is a _real_ problem.
> > > 
> > > Aren't we back to square one? My question is, how can users know it if
> > > somebody was OOM-killed needlessly by allowing MMF_OOM_SKIP to race.
> > > 
> > > You don't want to call get_page_from_freelist() from out_of_memory(), do you?
> > > But without passing a flag "whether get_page_from_freelist() with memory reserves
> > > was already attempted if current thread is an OOM victim" to task_will_free_mem()
> > > in out_of_memory() and a flag "whether get_page_from_freelist() without memory
> > > reserves was already attempted if current thread is not an OOM victim" to
> > > test_bit(MMF_OOM_SKIP) in oom_evaluate_task(), we won't be able to know
> > > if somebody was OOM-killed needlessly by allowing MMF_OOM_SKIP to race.
> > 
> > Michal, I did not get your answer, and your "mm, oom: do not rely on
> > TIF_MEMDIE for memory reserves access" did not help solving this problem.
> > (I confirmed it by reverting your "mm, oom: allow oom reaper to race with
> > exit_mmap" and applying Andrea's "mm: oom: let oom_reap_task and exit_mmap
> > run concurrently" and this patch on top of linux-next-20170817.)
> 
> By "this patch" you probably mean a BUG_ON(tsk_is_oom_victim) somewhere
> in task_will_free_mem right? I do not see anything like that in you
> email.

I wrote

  You can confirm it by adding "BUG_ON(1);" at "task->oom_kill_free_check_raced = 1;"
  of this patch.

in the patch description.

> 
> > [  204.413605] Out of memory: Kill process 9286 (a.out) score 930 or sacrifice child
> > [  204.416241] Killed process 9286 (a.out) total-vm:4198476kB, anon-rss:72kB, file-rss:0kB, shmem-rss:3465520kB
> > [  204.419783] oom_reaper: reaped process 9286 (a.out), now anon-rss:0kB, file-rss:0kB, shmem-rss:3465720kB
> > [  204.455864] ------------[ cut here ]------------
> > [  204.457921] kernel BUG at mm/oom_kill.c:786!
> > 
> > Therefore, I propose this patch for inclusion.
> 
> i've already told you that this is a wrong approach to handle a possible
> race and offered you an alternative. I realy fail to see why you keep
> reposting it. So to make myself absolutely clear
> 
> Nacked-by: Michal Hocko <mhocko@suse.com> to the patch below.

Where is your alternative?

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Date: Mon, 21 Aug 2017 14:10:22 +0200
From: Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH v2] mm, oom: task_will_free_mem(current) should ignore
 MMF_OOM_SKIP for once.
Message-ID: <20170821121022.GF25956@dhcp22.suse.cz>
References: <1501718104-8099-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
 <201708191523.BJH90621.MHOOFFQSOLJFtV@I-love.SAKURA.ne.jp>
 <20170821084307.GB25956@dhcp22.suse.cz>
 <201708212041.GAJ05272.VOMOJOFSQLFtHF@I-love.SAKURA.ne.jp>
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List-ID: <linux-mm.kvack.org>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org, rientjes@google.com, mjaggi@caviumnetworks.com, oleg@redhat.com, vdavydov@virtuozzo.com

On Mon 21-08-17 20:41:52, Tetsuo Handa wrote:
> Michal Hocko wrote:
> > On Sat 19-08-17 15:23:19, Tetsuo Handa wrote:
> > > Tetsuo Handa wrote at http://lkml.kernel.org/r/201708102328.ACD34352.OHFOLJMQVSFOFt@I-love.SAKURA.ne.jp :
> > > > Michal Hocko wrote:
> > > > > On Thu 10-08-17 21:10:30, Tetsuo Handa wrote:
> > > > > > Michal Hocko wrote:
> > > > > > > On Tue 08-08-17 11:14:50, Tetsuo Handa wrote:
> > > > > > > > Michal Hocko wrote:
> > > > > > > > > On Sat 05-08-17 10:02:55, Tetsuo Handa wrote:
> > > > > > > > > > Michal Hocko wrote:
> > > > > > > > > > > On Wed 26-07-17 20:33:21, Tetsuo Handa wrote:
> > > > > > > > > > > > My question is, how can users know it if somebody was OOM-killed needlessly
> > > > > > > > > > > > by allowing MMF_OOM_SKIP to race.
> > > > > > > > > > > 
> > > > > > > > > > > Is it really important to know that the race is due to MMF_OOM_SKIP?
> > > > > > > > > > 
> > > > > > > > > > Yes, it is really important. Needlessly selecting even one OOM victim is
> > > > > > > > > > a pain which is difficult to explain to and persuade some of customers.
> > > > > > > > > 
> > > > > > > > > How is this any different from a race with a task exiting an releasing
> > > > > > > > > some memory after we have crossed the point of no return and will kill
> > > > > > > > > something?
> > > > > > > > 
> > > > > > > > I'm not complaining about an exiting task releasing some memory after we have
> > > > > > > > crossed the point of no return.
> > > > > > > > 
> > > > > > > > What I'm saying is that we can postpone "the point of no return" if we ignore
> > > > > > > > MMF_OOM_SKIP for once (both this "oom_reaper: close race without using oom_lock"
> > > > > > > > thread and "mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for
> > > > > > > > once." thread). These are race conditions we can avoid without crystal ball.
> > > > > > > 
> > > > > > > If those races are really that common than we can handle them even
> > > > > > > without "try once more" tricks. Really this is just an ugly hack. If you
> > > > > > > really care then make sure that we always try to allocate from memory
> > > > > > > reserves before going down the oom path. In other words, try to find a
> > > > > > > robust solution rather than tweaks around a problem.
> > > > > > 
> > > > > > Since your "mm, oom: allow oom reaper to race with exit_mmap" patch removes
> > > > > > oom_lock serialization from the OOM reaper, possibility of calling out_of_memory()
> > > > > > due to successful mutex_trylock(&oom_lock) would increase when the OOM reaper set
> > > > > > MMF_OOM_SKIP quickly.
> > > > > > 
> > > > > > What if task_is_oom_victim(current) became true and MMF_OOM_SKIP was set
> > > > > > on current->mm between after __gfp_pfmemalloc_flags() returned 0 and before
> > > > > > out_of_memory() is called (due to successful mutex_trylock(&oom_lock)) ?
> > > > > > 
> > > > > > Excuse me? Are you suggesting to try memory reserves before
> > > > > > task_is_oom_victim(current) becomes true?
> > > > > 
> > > > > No what I've tried to say is that if this really is a real problem,
> > > > > which I am not sure about, then the proper way to handle that is to
> > > > > attempt to allocate from memory reserves for an oom victim. I would be
> > > > > even willing to take the oom_lock back into the oom reaper path if the
> > > > > former turnes out to be awkward to implement. But all this assumes this
> > > > > is a _real_ problem.
> > > > 
> > > > Aren't we back to square one? My question is, how can users know it if
> > > > somebody was OOM-killed needlessly by allowing MMF_OOM_SKIP to race.
> > > > 
> > > > You don't want to call get_page_from_freelist() from out_of_memory(), do you?
> > > > But without passing a flag "whether get_page_from_freelist() with memory reserves
> > > > was already attempted if current thread is an OOM victim" to task_will_free_mem()
> > > > in out_of_memory() and a flag "whether get_page_from_freelist() without memory
> > > > reserves was already attempted if current thread is not an OOM victim" to
> > > > test_bit(MMF_OOM_SKIP) in oom_evaluate_task(), we won't be able to know
> > > > if somebody was OOM-killed needlessly by allowing MMF_OOM_SKIP to race.
> > > 
> > > Michal, I did not get your answer, and your "mm, oom: do not rely on
> > > TIF_MEMDIE for memory reserves access" did not help solving this problem.
> > > (I confirmed it by reverting your "mm, oom: allow oom reaper to race with
> > > exit_mmap" and applying Andrea's "mm: oom: let oom_reap_task and exit_mmap
> > > run concurrently" and this patch on top of linux-next-20170817.)
> > 
> > By "this patch" you probably mean a BUG_ON(tsk_is_oom_victim) somewhere
> > in task_will_free_mem right? I do not see anything like that in you
> > email.
> 
> I wrote
> 
>   You can confirm it by adding "BUG_ON(1);" at "task->oom_kill_free_check_raced = 1;"
>   of this patch.
> 
> in the patch description.

Ahh, OK so it was in the changelog. Your wording suggested a debugging
patch which you forgot to add.
 
> > 
> > > [  204.413605] Out of memory: Kill process 9286 (a.out) score 930 or sacrifice child
> > > [  204.416241] Killed process 9286 (a.out) total-vm:4198476kB, anon-rss:72kB, file-rss:0kB, shmem-rss:3465520kB
> > > [  204.419783] oom_reaper: reaped process 9286 (a.out), now anon-rss:0kB, file-rss:0kB, shmem-rss:3465720kB
> > > [  204.455864] ------------[ cut here ]------------
> > > [  204.457921] kernel BUG at mm/oom_kill.c:786!
> > > 
> > > Therefore, I propose this patch for inclusion.
> > 
> > i've already told you that this is a wrong approach to handle a possible
> > race and offered you an alternative. I realy fail to see why you keep
> > reposting it. So to make myself absolutely clear
> > 
> > Nacked-by: Michal Hocko <mhocko@suse.com> to the patch below.
> 
> Where is your alternative?

Sigh... Let me repeat for the last time (this whole thread is largely a
waste of time to be honest). Find a _robust_ solution rather than
fiddling with try-once-more kind of hacks. E.g. do an allocation attempt
_before_ we do any disruptive action (aka kill a victim). This would
help other cases when we race with an exiting tasks or somebody managed
to free memory while we were selecting an oom victim which can take
quite some time.
-- 
Michal Hocko
SUSE Labs

--
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Subject: Re: [PATCH v2] mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for once.
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
References: <1501718104-8099-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
	<201708191523.BJH90621.MHOOFFQSOLJFtV@I-love.SAKURA.ne.jp>
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	<20170821121022.GF25956@dhcp22.suse.cz>
In-Reply-To: <20170821121022.GF25956@dhcp22.suse.cz>
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Michal Hocko wrote:
> On Mon 21-08-17 20:41:52, Tetsuo Handa wrote:
> > Michal Hocko wrote:
> > > On Sat 19-08-17 15:23:19, Tetsuo Handa wrote:
> > > > Tetsuo Handa wrote at http://lkml.kernel.org/r/201708102328.ACD34352.OHFOLJMQVSFOFt@I-love.SAKURA.ne.jp :
> > > > > Michal Hocko wrote:
> > > > > > On Thu 10-08-17 21:10:30, Tetsuo Handa wrote:
> > > > > > > Michal Hocko wrote:
> > > > > > > > On Tue 08-08-17 11:14:50, Tetsuo Handa wrote:
> > > > > > > > > Michal Hocko wrote:
> > > > > > > > > > On Sat 05-08-17 10:02:55, Tetsuo Handa wrote:
> > > > > > > > > > > Michal Hocko wrote:
> > > > > > > > > > > > On Wed 26-07-17 20:33:21, Tetsuo Handa wrote:
> > > > > > > > > > > > > My question is, how can users know it if somebody was OOM-killed needlessly
> > > > > > > > > > > > > by allowing MMF_OOM_SKIP to race.
> > > > > > > > > > > > 
> > > > > > > > > > > > Is it really important to know that the race is due to MMF_OOM_SKIP?
> > > > > > > > > > > 
> > > > > > > > > > > Yes, it is really important. Needlessly selecting even one OOM victim is
> > > > > > > > > > > a pain which is difficult to explain to and persuade some of customers.
> > > > > > > > > > 
> > > > > > > > > > How is this any different from a race with a task exiting an releasing
> > > > > > > > > > some memory after we have crossed the point of no return and will kill
> > > > > > > > > > something?
> > > > > > > > > 
> > > > > > > > > I'm not complaining about an exiting task releasing some memory after we have
> > > > > > > > > crossed the point of no return.
> > > > > > > > > 
> > > > > > > > > What I'm saying is that we can postpone "the point of no return" if we ignore
> > > > > > > > > MMF_OOM_SKIP for once (both this "oom_reaper: close race without using oom_lock"
> > > > > > > > > thread and "mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for
> > > > > > > > > once." thread). These are race conditions we can avoid without crystal ball.
> > > > > > > > 
> > > > > > > > If those races are really that common than we can handle them even
> > > > > > > > without "try once more" tricks. Really this is just an ugly hack. If you
> > > > > > > > really care then make sure that we always try to allocate from memory
> > > > > > > > reserves before going down the oom path. In other words, try to find a
> > > > > > > > robust solution rather than tweaks around a problem.
> > > > > > > 
> > > > > > > Since your "mm, oom: allow oom reaper to race with exit_mmap" patch removes
> > > > > > > oom_lock serialization from the OOM reaper, possibility of calling out_of_memory()
> > > > > > > due to successful mutex_trylock(&oom_lock) would increase when the OOM reaper set
> > > > > > > MMF_OOM_SKIP quickly.
> > > > > > > 
> > > > > > > What if task_is_oom_victim(current) became true and MMF_OOM_SKIP was set
> > > > > > > on current->mm between after __gfp_pfmemalloc_flags() returned 0 and before
> > > > > > > out_of_memory() is called (due to successful mutex_trylock(&oom_lock)) ?
> > > > > > > 
> > > > > > > Excuse me? Are you suggesting to try memory reserves before
> > > > > > > task_is_oom_victim(current) becomes true?
> > > > > > 
> > > > > > No what I've tried to say is that if this really is a real problem,
> > > > > > which I am not sure about, then the proper way to handle that is to
> > > > > > attempt to allocate from memory reserves for an oom victim. I would be
> > > > > > even willing to take the oom_lock back into the oom reaper path if the
> > > > > > former turnes out to be awkward to implement. But all this assumes this
> > > > > > is a _real_ problem.
> > > > > 
> > > > > Aren't we back to square one? My question is, how can users know it if
> > > > > somebody was OOM-killed needlessly by allowing MMF_OOM_SKIP to race.
> > > > > 
> > > > > You don't want to call get_page_from_freelist() from out_of_memory(), do you?
> > > > > But without passing a flag "whether get_page_from_freelist() with memory reserves
> > > > > was already attempted if current thread is an OOM victim" to task_will_free_mem()
> > > > > in out_of_memory() and a flag "whether get_page_from_freelist() without memory
> > > > > reserves was already attempted if current thread is not an OOM victim" to
> > > > > test_bit(MMF_OOM_SKIP) in oom_evaluate_task(), we won't be able to know
> > > > > if somebody was OOM-killed needlessly by allowing MMF_OOM_SKIP to race.
> > > > 
> > > > Michal, I did not get your answer, and your "mm, oom: do not rely on
> > > > TIF_MEMDIE for memory reserves access" did not help solving this problem.
> > > > (I confirmed it by reverting your "mm, oom: allow oom reaper to race with
> > > > exit_mmap" and applying Andrea's "mm: oom: let oom_reap_task and exit_mmap
> > > > run concurrently" and this patch on top of linux-next-20170817.)
> > > 
> > > By "this patch" you probably mean a BUG_ON(tsk_is_oom_victim) somewhere
> > > in task_will_free_mem right? I do not see anything like that in you
> > > email.
> > 
> > I wrote
> > 
> >   You can confirm it by adding "BUG_ON(1);" at "task->oom_kill_free_check_raced = 1;"
> >   of this patch.
> > 
> > in the patch description.
> 
> Ahh, OK so it was in the changelog. Your wording suggested a debugging
> patch which you forgot to add.
>  
> > > 
> > > > [  204.413605] Out of memory: Kill process 9286 (a.out) score 930 or sacrifice child
> > > > [  204.416241] Killed process 9286 (a.out) total-vm:4198476kB, anon-rss:72kB, file-rss:0kB, shmem-rss:3465520kB
> > > > [  204.419783] oom_reaper: reaped process 9286 (a.out), now anon-rss:0kB, file-rss:0kB, shmem-rss:3465720kB
> > > > [  204.455864] ------------[ cut here ]------------
> > > > [  204.457921] kernel BUG at mm/oom_kill.c:786!
> > > > 
> > > > Therefore, I propose this patch for inclusion.
> > > 
> > > i've already told you that this is a wrong approach to handle a possible
> > > race and offered you an alternative. I realy fail to see why you keep
> > > reposting it. So to make myself absolutely clear
> > > 
> > > Nacked-by: Michal Hocko <mhocko@suse.com> to the patch below.
> > 
> > Where is your alternative?
> 
> Sigh... Let me repeat for the last time (this whole thread is largely a
> waste of time to be honest). Find a _robust_ solution rather than
> fiddling with try-once-more kind of hacks. E.g. do an allocation attempt
> _before_ we do any disruptive action (aka kill a victim). This would
> help other cases when we race with an exiting tasks or somebody managed
> to free memory while we were selecting an oom victim which can take
> quite some time.

I did not get your answer to my question:

  You don't want to call get_page_from_freelist() from out_of_memory(), do you?

Since David Rientjes wrote "how sloppy this would be because it's blurring
the line between oom killer and page allocator." and you responded as
"Yes the layer violation is definitely not nice." at
http://lkml.kernel.org/r/20160129152307.GF32174@dhcp22.suse.cz ,
I assumed that you don't want to call get_page_from_freelist() from out_of_memory().

But now, you are suggesting to do an allocation attempt _before_ we do any disruptive action.
Did you change your mind to accept calling get_page_from_freelist() from out_of_memory() ?
If yes, I will try to write such patch.

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Date: Mon, 21 Aug 2017 15:18:52 +0200
From: Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH v2] mm, oom: task_will_free_mem(current) should ignore
 MMF_OOM_SKIP for once.
Message-ID: <20170821131851.GJ25956@dhcp22.suse.cz>
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To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org, rientjes@google.com, mjaggi@caviumnetworks.com, oleg@redhat.com, vdavydov.dev@gmail.com

On Mon 21-08-17 21:57:44, Tetsuo Handa wrote:
> Michal Hocko wrote:
[...]
> > Sigh... Let me repeat for the last time (this whole thread is largely a
> > waste of time to be honest). Find a _robust_ solution rather than
> > fiddling with try-once-more kind of hacks. E.g. do an allocation attempt
> > _before_ we do any disruptive action (aka kill a victim). This would
> > help other cases when we race with an exiting tasks or somebody managed
> > to free memory while we were selecting an oom victim which can take
> > quite some time.
> 
> I did not get your answer to my question:
> 
>   You don't want to call get_page_from_freelist() from out_of_memory(), do you?
> 
> Since David Rientjes wrote "how sloppy this would be because it's blurring
> the line between oom killer and page allocator." and you responded as
> "Yes the layer violation is definitely not nice." at
> http://lkml.kernel.org/r/20160129152307.GF32174@dhcp22.suse.cz ,
> I assumed that you don't want to call get_page_from_freelist() from out_of_memory().

Yes that would be a layering violation and I do not like that very much.
And that is why I keep repeating that this is something to handle only _if_
the problem is real and happens with _sensible_ workloads so often that
we really have to care. If this happens only under oom stress testing
then I would be tempted to not care all that much.

Please try to understand that OOM killer will never be perfect and
adding more kludges and hacks make it more fragile so each additional
heuristic should be considered carefully.
-- 
Michal Hocko
SUSE Labs

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