linux-kernel - Re: [PATCH V7 1/2] cgroup/rstat: Avoid thundering herd problem by kswapd across NUMA nodes

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Message-ID: <iso3venoxgfdd6mtc6xatahxqqpev3ddl3sry72aoprpbavt5h@izhokjdp6ga6>
Date: Fri, 19 Jul 2024 15:47:52 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Jesper Dangaard Brouer <hawk@...nel.org>
Cc: Yosry Ahmed <yosryahmed@...gle.com>, tj@...nel.org, 
	cgroups@...r.kernel.org, hannes@...xchg.org, lizefan.x@...edance.com, longman@...hat.com, 
	kernel-team@...udflare.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V7 1/2] cgroup/rstat: Avoid thundering herd problem by
 kswapd across NUMA nodes

On Fri, Jul 19, 2024 at 09:54:41AM GMT, Jesper Dangaard Brouer wrote:
> 
> 
> On 19/07/2024 02.40, Shakeel Butt wrote:
> > Hi Jesper,
> > 
> > On Wed, Jul 17, 2024 at 06:36:28PM GMT, Jesper Dangaard Brouer wrote:
> > > 
> > [...]
> > > 
> > > 
> > > Looking at the production numbers for the time the lock is held for level 0:
> > > 
> > > @locked_time_level[0]:
> > > [4M, 8M)     623 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@               |
> > > [8M, 16M)    860 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
> > > [16M, 32M)   295 |@@@@@@@@@@@@@@@@@                                   |
> > > [32M, 64M)   275 |@@@@@@@@@@@@@@@@                                    |
> > > 
> > 
> > Is it possible to get the above histogram for other levels as well?
> 
> Data from other levels available in [1]:
>  [1]
> https://lore.kernel.org/all/8c123882-a5c5-409a-938b-cb5aec9b9ab5@kernel.org/
> 
> IMHO the data shows we will get most out of skipping level-0 root-cgroup
> flushes.
> 

Thanks a lot of the data. Are all or most of these locked_time_level[0]
from kswapds? This just motivates me to strongly push the ratelimited
flush patch of mine (which would be orthogonal to your patch series).

Shakeel