linux-kernel - Re: [PATCH RFC] mm: Avoid triggering oom-killer during memory hot-remove operations

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Message-ID: <Zqdd25XhcEDPEQIS@tiehlicka>
Date: Mon, 29 Jul 2024 11:16:11 +0200
From: Michal Hocko <mhocko@...e.com>
To: "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>
Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>,
	Oscar Salvador <osalvador@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Yasunori Gotou (Fujitsu)" <y-goto@...itsu.com>
Subject: Re: [PATCH RFC] mm: Avoid triggering oom-killer during memory
 hot-remove operations

On Mon 29-07-24 08:53:11, Zhijian Li (Fujitsu) wrote:
[...]
> >>>> [13853.758192] pagefault_out_of_memory: 4055 callbacks suppressed
> >>>> [13853.758243] Huh VM_FAULT_OOM leaked out to the #PF handler. Retrying PF
> >>>
> >>> This shouldn't really happen and it indicates that some memory
> >>> allocation in the pagefault path has failed.
> >>
> >> May I know if this will cause side effect to other processes.
> > 
> > This eill mean that the #PF handler has failed to allocate memory and
> > the VM_FAULT_OOM error has unwound all the way up to the exception
> > handler and that will restart the instruction that has caused the #PF.
> > > In essence, as long as the process triggering this is not killed or the
> > allocation doesn't suceed it will be looping in the #PF path. This
> > normally doesn't happen because our allocators do not fail for small
> > allocation requests.
> 
> Thanks again for your detailed explanation.
> 
> I think this is acceptable for the process bound to the being removed node, isn't it?

It shouldn't be happening really. This is a sign that something doesn't
behave properly. E.g. some of the #PF returning VM_FAULT_OOM without
calling into the allocator.

-- 
Michal Hocko
SUSE Labs