linux-kernel - Re: [PATCH mm v2] vmalloc: back off when the current task is OOM-killed

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Message-ID: <dd6f3cc5-70f3-4275-6458-118c463bf38a@virtuozzo.com>
Date:   Tue, 5 Oct 2021 17:00:05 +0300
From:   Vasily Averin <vvs@...tuozzo.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel@...nvz.org
Subject: Re: [PATCH mm v2] vmalloc: back off when the current task is
 OOM-killed

On 10/5/21 4:52 PM, Vasily Averin wrote:
> Huge vmalloc allocation on heavy loaded node can lead to a global
> memory shortage. Task called vmalloc can have worst badness and
> be selected by OOM-killer, however taken fatal signal does not
> interrupt allocation cycle. Vmalloc repeat page allocaions
> again and again, exacerbating the crisis and consuming the memory
> freed up by another killed tasks.
> 
> After a successful completion of the allocation procedure, a fatal
> signal will be processed and task will be destroyed finally.
> However it may not release the consumed memory, since the allocated
> object may have a lifetime unrelated to the completed task.
> In the worst case, this can lead to the host will panic
> due to "Out of memory and no killable processes..."
> 
> This patch allows OOM-killer to break vmalloc cycle, makes OOM more
> effective and avoid host panic. It does not check oom condition directly,
> however, and breaks page allocation cycle when fatal signal was received.
> 
> This may trigger some hidden problems, when caller does not handle
> vmalloc failures, or when rollaback after failed vmalloc calls own
> vmallocs inside. However all of these scenarios are incorrect:
> vmalloc does not guarantee successful allocation, it has never been called
> with __GFP_NOFAIL and threfore either should not be used for any rollbacks
> or should handle such errors correctly and not lead to critical
> failures.

I briefly checked this patch together with 
 v3 memcg: prohibit unconditional exceeding the limit of dying tasks
 over v5.15-rc4.
I executed LTP on host, all oom, cgroup and memcg tests was successfully finished.
and then experimented with memcg limited LXC containers.
I did not noticed any troubles on my test node.
Thank you,
	Vasily Averin