linux-kernel - Re: [PATCH mm-unstable v1 0/2] Track pages allocated for struct

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Message-Id: <20241031160604.bcd5740390f05a01409b64f3@linux-foundation.org>
Date: Thu, 31 Oct 2024 16:06:04 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Kinsey Ho <kinseyho@...gle.com>
Cc: Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>,
 Roman Gushchin <roman.gushchin@...ux.dev>, Shakeel Butt
 <shakeel.butt@...ux.dev>, Muchun Song <muchun.song@...ux.dev>, Pasha
 Tatashin <pasha.tatashin@...een.com>, David Rientjes <rientjes@...gle.com>,
 willy@...radead.org, Vlastimil Babka <vbabka@...e.cz>, David Hildenbrand
 <david@...hat.com>, Joel Granados <joel.granados@...nel.org>, Kaiyang Zhao
 <kaiyang2@...cmu.edu>, Sourav Panda <souravpanda@...gle.com>,
 linux-kernel@...r.kernel.org, cgroups@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH mm-unstable v1 0/2] Track pages allocated for struct

hm.

On Thu, 31 Oct 2024 22:45:49 +0000 Kinsey Ho <kinseyho@...gle.com> wrote:

> We noticed high overhead for pages allocated for struct swap_cgroup in
> our fleet.

This is scanty.  Please describe the problem further.

> This patchset adds the number of pages allocated for struct
> swap_cgroup to vmstat. This can be a useful metric for identifying
> unneeded overhead on systems which configure swap.

Possibly dumb question: can we switch swap_cgroup_prepare to kmalloc()
(or kmem-cache_alloc()) and use slab's accounting to satisfy this
requirement?

> Before adding the new stat, Patch 1 introduces a generic system-wide
> counting interface. 

I don't really understand this one and would like to hear much more
about the motivation.

And: "the existing use case" is OK with a global counter, but what about
future use cases?

And: what are the future use cases?

Thanks.