linux-kernel - Re: [PATCH RFC 2/2] mm: kmem: add direct objcg pointer to task

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Date:   Mon, 2 Jan 2023 17:09:46 +0100
From:   Michal Koutný <mkoutny@...e.com>
To:     Roman Gushchin <roman.gushchin@...ux.dev>
Cc:     linux-mm@...ck.org, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, Shakeel Butt <shakeelb@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Muchun Song <muchun.song@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH RFC 2/2] mm: kmem: add direct objcg pointer to task_struct

Hello.

On Thu, Dec 22, 2022 at 08:21:49AM -0800, Roman Gushchin <roman.gushchin@...ux.dev> wrote:
> Do you have any numbers to share?

The numbers are in bko#216038, let me explain them here a bit.
I used the will-it-scale benchmark that repeatedly locks/unlocks a file
and runs in parallel.

The final numbers were:
  sample			metric	 	  δ	 δ_cg
  no accounting implemented	32307750	  0 %	 
  accounting in cg		2.49577e+07	-23 %	 0 %
  accounting in cg + cache	2.51642e+07 	-22 %	+1 %

Hence my result was only 1% improvement.

(But it was a very simple try, not delving into any of the CPU cache
statistics.)

Question: Were your measurements multi-threaded?

> 1) some people periodically complain that accounted allocations are slow
>    in comparison to non-accounted and slower than they were with page-based
>    accounting,

My result above would not likely satisfy those complainers I know about.
But if your additional changes are better the additional code complexity
may be justified in the end.


> Btw, I'm working on a patch 3 for this series, which in early tests brings
> additional ~25% improvement in my benchmark, hopefully will post it soon as
> a part of v1.

Please send it with more details about your benchmark to put the numbers
into context.


Michal

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