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

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Date:   Thu, 7 Oct 2021 12:47:53 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Vasily Averin <vvs@...tuozzo.com>
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 Tue 05-10-21 16:52:40, 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 will allow also interrupting a user space requist which happens to
trigger a large vmalloc, hence the reason for going for
fatal_signal_pending rather than oom specific condition.

> 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.

__GFP_NOFAIL semantic is explicitly not supported for vmalloc.

> Signed-off-by: Vasily Averin <vvs@...tuozzo.com>

Acked-by: Michal Hocko <mhocko@...e.com>

I would keep it sitting in the linux-next for some time to sort out
potential fallouts and have them fixed before this one gets merged.

Thanks!
> ---
> v2: tsk_is_oom_victim() check replaced by fatal_signal_pending(current),
>     removed check inside __alloc_pages_bulk(),
>     according to feedback from mhocko@.
>     Updated patch description.
> ---
>  mm/vmalloc.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index d77830ff604c..71706f5447f0 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2860,6 +2860,9 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>  		struct page *page;
>  		int i;
>  
> +		if (fatal_signal_pending(current))
> +			break;
> +
>  		page = alloc_pages_node(nid, gfp, order);
>  		if (unlikely(!page))
>  			break;
> -- 
> 2.31.1

-- 
Michal Hocko
SUSE Labs