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

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Message-ID: <axnnvibukeqk6l4mijzy4yv73zlzoecbctfb2smw45qs2pwmlc@srlg4hlujaj5>
Date: Thu, 3 Apr 2025 11:23:53 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Johannes Weiner <hannes@...xchg.org>
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 Thu, Apr 03, 2025 at 12:47:41PM -0400, Johannes Weiner wrote:
> 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?

Yes, it can be a regular vmstat item (enum node_stat_item). However then
we have go over each page as node_stat_item are per-node and vmalloc
region can have pages from different nodes (I think but let me check).