linux-kernel - Re: [PATCH v2 3/7] memcg: reduce memory for the lruvec and memcg stats

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Message-ID: <sskkbmc36fljo5xj3mn4fufctu3lvk3ubkxzy5mif4wsxe2zou@4oyulvmduhbk>
Date: Mon, 29 Apr 2024 13:00:06 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Roman Gushchin <roman.gushchin@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, 
	Muchun Song <muchun.song@...ux.dev>, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/7] memcg: reduce memory for the lruvec and memcg
 stats

On Mon, Apr 29, 2024 at 09:00:16AM -0700, Roman Gushchin wrote:
> On Fri, Apr 26, 2024 at 05:37:29PM -0700, Shakeel Butt wrote:
[...]
> 
> Hm, I'm slightly worried about the performance penalty due to the increased cache
> footprint. Can't we have some formula to translate idx to memcg_idx instead of
> a translation table?
> If it requires a re-arrangement of items we can add a translation table on the
> read side to save the visible order in procfs/sysfs.
> Or I'm overthinking and the real difference is negligible?
> 

No, you are not overthinking and the update side is very performance
sensitive. On my simple testing I do not see any regression but I am
hoping that the Intel's performance bot will tell us if this is really
worth exploring.

> Thanks!