linux-kernel - Re: [PATCH rfc 0/5] mm: introduce shrinker sysfs interface

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Message-ID: <Yl0vCDE44VeU8qxC@kernel.org>
Date:   Mon, 18 Apr 2022 12:27:36 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Roman Gushchin <roman.gushchin@...ux.dev>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Dave Chinner <dchinner@...hat.com>,
        linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Yang Shi <shy828301@...il.com>
Subject: Re: [PATCH rfc 0/5] mm: introduce shrinker sysfs interface

On Fri, Apr 15, 2022 at 05:27:51PM -0700, Roman Gushchin wrote:
> There are 50+ different shrinkers in the kernel, many with their own bells and
> whistles. Under the memory pressure the kernel applies some pressure on each of
> them in the order of which they were created/registered in the system. Some
> of them can contain only few objects, some can be quite large. Some can be
> effective at reclaiming memory, some not.
> 
> The only existing debugging mechanism is a couple of tracepoints in
> do_shrink_slab(): mm_shrink_slab_start and mm_shrink_slab_end. They aren't
> covering everything though: shrinkers which report 0 objects will never show up,
> there is no support for memcg-aware shrinkers. Shrinkers are identified by their
> scan function, which is not always enough (e.g. hard to guess which super
> block's shrinker it is having only "super_cache_scan"). They are a passive
> mechanism: there is no way to call into counting and scanning of an individual
> shrinker and profile it.
> 
> To provide a better visibility and debug options for memory shrinkers
> this patchset introduces a /sys/kernel/shrinker interface, to some extent
> similar to /sys/kernel/slab.

Wouldn't debugfs better fit the purpose of shrinker debugging?
 
-- 
Sincerely yours,
Mike.