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

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Date:   Thu, 21 Apr 2022 11:18:20 +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 Wed 20-04-22 12:58:05, Kent Overstreet wrote:
> On Wed, Apr 20, 2022 at 08:58:36AM +0200, Michal Hocko wrote:
> > On Tue 19-04-22 16:32:01, Kent Overstreet wrote:
> > > This patch:
> > >  - Moves lib/show_mem.c to mm/show_mem.c
> > 
> > Sure, why not. Should be a separate patch.
> > 
> > >  - Changes show_mem() to always report on slab usage
> > >  - Instead of reporting on all slabs, we only report on top 10 slabs,
> > >    and in sorted order
> > >  - Also reports on shrinkers, with the new shrinkers_to_text().
> > 
> > Why do we need/want this? It would be also great to provide an example
> > of why the new output is better (in which cases) than the existing one.
> 
> Did you read the cover letter to the patch series?

Nope, only this one made it into my inbox based on my filters. I usually
try to fish out other parts of the thread but I didn't this time.
Besides it is always better to have a full patch description explain not
only what has been changed but why as well.

> But sure, I can give you an example of the new output:

Calling out the changes would be really helpful, but I guess the crux 
is here.

> 00177 16644 pages reserved
> 00177 Unreclaimable slab info:
> 00177 9p-fcall-cache    total: 8.25 MiB active: 8.25 MiB
> 00177 kernfs_node_cache total: 2.15 MiB active: 2.15 MiB
> 00177 kmalloc-64        total: 2.08 MiB active: 2.07 MiB
> 00177 task_struct       total: 1.95 MiB active: 1.95 MiB
> 00177 kmalloc-4k        total: 1.50 MiB active: 1.50 MiB
> 00177 signal_cache      total: 1.34 MiB active: 1.34 MiB
> 00177 kmalloc-2k        total: 1.16 MiB active: 1.16 MiB
> 00177 bch_inode_info    total: 1.02 MiB active: 922 KiB
> 00177 perf_event        total: 1.02 MiB active: 1.02 MiB
> 00177 biovec-max        total: 992 KiB active: 960 KiB
> 00177 Shrinkers:
> 00177 super_cache_scan: objects: 127
> 00177 super_cache_scan: objects: 106
> 00177 jbd2_journal_shrink_scan: objects: 32
> 00177 ext4_es_scan: objects: 32
> 00177 bch2_btree_cache_scan: objects: 8
> 00177   nr nodes:          24
> 00177   nr dirty:          0
> 00177   cannibalize lock:  0000000000000000
> 00177 
> 00177 super_cache_scan: objects: 8
> 00177 super_cache_scan: objects: 1

How does this help to analyze this allocation failure?
-- 
Michal Hocko
SUSE Labs