linux-kernel - Re: [PATCH V3 3/3] mm: page_alloc: drain pcp lists before oom kill

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Date:   Wed, 15 Nov 2023 15:09:45 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Charan Teja Kalla <quic_charante@...cinc.com>
Cc:     akpm@...ux-foundation.org, mgorman@...hsingularity.net,
        david@...hat.com, vbabka@...e.cz, hannes@...xchg.org,
        quic_pkondeti@...cinc.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 3/3] mm: page_alloc: drain pcp lists before oom kill

On Tue 14-11-23 22:06:45, Charan Teja Kalla wrote:
> Thanks Michal!!
> 
> On 11/14/2023 4:18 PM, Michal Hocko wrote:
> >> At least in my particular stress test case it just delayed the OOM as i
> >> can see that at the time of OOM kill, there are no free pcp pages. My
> >> understanding of the OOM is that it should be the last resort and only
> >> after doing the enough reclaim retries. CMIW here.
> > Yes it is a last resort but it is a heuristic as well. So the real
> > questoin is whether this makes any practical difference outside of
> > artificial workloads. I do not see anything particularly worrying to
> > drain the pcp cache but it should be noted that this won't be 100%
> > either as racing freeing of memory will end up on pcp lists first.
> 
> Okay, I don't have any practical scenario where this helped me in
> avoiding the OOM.  Will comeback If I ever encounter this issue in
> practical scenario.
> 
> Also If you have any comments on [PATCH V2 2/3] mm: page_alloc: correct
> high atomic reserve calculations will help me.

I do not have a strong opinion on that one to be honest. I am not even
sure that reserving a full page block (4MB) on small systems as
presented is really a good use of memory.
-- 
Michal Hocko
SUSE Labs