linux-kernel - Re: [PATCH 3/4] mm: Centralize & improve oom reporting in show

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Message-ID: <YmKInWEihG+7mkU6@dhcp22.suse.cz>
Date:   Fri, 22 Apr 2022 12:51:09 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Kent Overstreet <kent.overstreet@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, roman.gushchin@...ux.dev,
        hannes@...xchg.org
Subject: Re: [PATCH 3/4] mm: Centralize & improve oom reporting in show_mem.c

On Fri 22-04-22 05:44:13, Kent Overstreet wrote:
> On Fri, Apr 22, 2022 at 11:27:05AM +0200, Michal Hocko wrote:
> > We already do that in some form. We dump unreclaimable slabs if they
> > consume more memory than user pages on LRUs. We also dump all slab
> > caches with some objects. Why is this approach not good? Should we tweak
> > the condition to dump or should we limit the dump? These are reasonable 
> > questions to ask. Your patch has dropped those without explaining any
> > of the motivation.
> > 
> > I am perfectly OK to modify should_dump_unreclaim_slab to dump even if
> > the slab memory consumption is lower. Also dumping small caches with
> > handful of objects can be excessive.
> > 
> > Wrt to shrinkers I really do not know what kind of shrinkers data would
> > be useful to dump and when. Therefore I am asking about examples.
> 
> Look, I've given you the sample

That sample is of no use as it doesn't really show how the additional
information is useful to analyze the allocation failure. I thought we
have agreed on that. You still haven't given any example where the
information is useful. So I do not really see any reason to change the
existing output.

> output you asked for and explained repeatedly my
> rationale and you haven't directly responded;

Your rationale is that we need more data and I do agree but it is not
clear which data and under which conditions.

> if you have a reason you're
> against the patches please say so, but please give your reasoning.

I have expressed that already, I believe, but let me repeat. I do not
like altering the oom report without a justification on how this new
output is useful. You have failed to explained that so far.
-- 
Michal Hocko
SUSE Labs