linux-kernel - Re: [PATCH] memcg: multi-memcg percpu charge cache

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Message-ID: <qt5jtbsgjym655tbnoddlo5c7cemndcgsqwy4wp7m7ki3venxz@cfp637s7eqo6>
Date: Tue, 29 Apr 2025 11:43:29 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Michal Hocko <mhocko@...e.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	Johannes Weiner <hannes@...xchg.org>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Muchun Song <muchun.song@...ux.dev>, Vlastimil Babka <vbabka@...e.cz>, 
	Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>, 
	Soheil Hassas Yeganeh <soheil@...gle.com>, linux-mm@...ck.org, cgroups@...r.kernel.org, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Meta kernel team <kernel-team@...a.com>
Subject: Re: [PATCH] memcg: multi-memcg percpu charge cache

On Tue, Apr 29, 2025 at 02:13:16PM +0200, Michal Hocko wrote:
> 
> > Some of the design choices are:
> > 
> > 1. Fit all caches memcgs in a single cacheline.
> 
> Could you be more specific about the reasoning? I suspect it is for the
> network receive path you are mentioning above, right?
> 

Here I meant why I chose NR_MEMCG_STOCK to be 7. Basically the first
cacheline of per-cpu stock has all the cached memcg, so checking if a
given memcg is cached or not should be comparable cheap as single cached
memcg. You suggested comment already mentioned this.

However please note that we may find in future that 2 cachelines worth of
cached memcgs are better for wider audience/workloads but for simplicity
let's start with single cacheline worth of cached memcgs.

[...]
> 
> Just a minor suggestion below. Other than that looks good to me (with
> follow up fixes) in this thread.
> Acked-by: Michal Hocko <mhocko@...e.com>
> Thanks!
> 

Thanks, I will send a diff for Andrew to squash it into original patch.