linux-kernel - Re: [PATCH] memcg: vmalloc: simplify MEMCG

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Message-ID: <20250403164741.GB368504@cmpxchg.org>
Date: Thu, 3 Apr 2025 12:47:41 -0400
From: Johannes Weiner <hannes@...xchg.org>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	Meta kernel team <kernel-team@...a.com>
Subject: Re: [PATCH] memcg: vmalloc: simplify MEMCG_VMALLOC updates

On Wed, Apr 02, 2025 at 10:33:26PM -0700, Shakeel Butt wrote:
> The vmalloc region can either be charged to a single memcg or none. At
> the moment kernel traverses all the pages backing the vmalloc region to
> update the MEMCG_VMALLOC stat. However there is no need to look at all
> the pages as all those pages will be charged to a single memcg or none.
> Simplify the MEMCG_VMALLOC update by just looking at the first page of
> the vmalloc region.
> 
> Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>

It's definitely pointless to handle each page with the stat being
per-cgroup only. But I do wonder why it's not a regular vmstat item.

There is no real reason it *should* be a private memcg stat, is there?