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

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Date:   Tue, 19 Apr 2022 14:36:54 -0400
From:   Kent Overstreet <kent.overstreet@...il.com>
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>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH rfc 0/5] mm: introduce shrinker sysfs interface

On Fri, Apr 15, 2022 at 05:27:51PM -0700, Roman Gushchin wrote:
> 7) Don't display cgroups with less than 500 attached objects
>   $ echo 500 > count_memcg
>   $ cat count_memcg
>     53 817
>     1868 886
>     2396 799
>     2462 861
> 
> 8) Don't display cgroups with less than 500 attached objects (sum over all nodes)
>   $ echo "500" > count_memcg_node
>   $ cat count_memcg_node
>     53 810 7
>     1868 886 0
>     2396 799 0
>     2462 861 0
> 
> 9) Scan system/root shrinker
>   $ cat count
>     212
>   $ echo 100 > scan
>   $ cat scan
>     97
>   $ cat count
>     115

This part seems entirely overengineered though and a really bad idea - can we
please _not_ store query state in the kernel? It's not thread safe, and it seems
like overengineering before we've done the basics (just getting this stuff in
sysfs is a major improvement!).

I know kmemleak does something kinda sorta like this, but that's a special
purpose debugging tool and this looks to be something more general purpose
that'll get used in production.