linux-kernel - Re: [PATCH v1] mm: zswap: add per-memcg stat for incompressible pages

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Message-ID: <CAKEwX=PBsuO27n_Vw112Ss2ZCTFqGem8f134cGKbHUQVL0aQ9g@mail.gmail.com>
Date: Thu, 5 Feb 2026 09:45:25 -0800
From: Nhat Pham <nphamcs@...il.com>
To: Jiayuan Chen <jiayuan.chen@...ux.dev>
Cc: linux-mm@...ck.org, Jiayuan Chen <jiayuan.chen@...pee.com>, 
	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>, Yosry Ahmed <yosry.ahmed@...ux.dev>, 
	Chengming Zhou <chengming.zhou@...ux.dev>, Andrew Morton <akpm@...ux-foundation.org>, 
	Nick Terrell <terrelln@...com>, David Sterba <dsterba@...e.com>, cgroups@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Chris Li <chrisl@...nel.org>
Subject: Re: [PATCH v1] mm: zswap: add per-memcg stat for incompressible pages

On Thu, Feb 5, 2026 at 9:31 AM Nhat Pham <nphamcs@...il.com> wrote:
>
> On Wed, Feb 4, 2026 at 9:31 PM Jiayuan Chen <jiayuan.chen@...ux.dev> wrote:
> >
> > From: Jiayuan Chen <jiayuan.chen@...pee.com>
> >
> > The global zswap_stored_incompressible_pages counter was added in commit
> > dca4437a5861 ("mm/zswap: store <PAGE_SIZE compression failed page as-is")
> > to track how many pages are stored in raw (uncompressed) form in zswap.
> > However, in containerized environments, knowing which cgroup is
> > contributing incompressible pages is essential for effective resource
> > management.
> >
> > Add a new memcg stat 'zswpraw' to track incompressible pages per cgroup.
> > This helps administrators and orchestrators to:
> >
> > 1. Identify workloads that produce incompressible data (e.g., encrypted
> >    data, already-compressed media, random data) and may not benefit from
> >    zswap.
> >
> > 2. Make informed decisions about workload placement - moving
> >    incompressible workloads to nodes with larger swap backing devices
> >    rather than relying on zswap.
> >
> > 3. Debug zswap efficiency issues at the cgroup level without needing to
> >    correlate global stats with individual cgroups.
> >
> > While the compression ratio can be estimated from existing stats
> > (zswap / zswapped * PAGE_SIZE), this doesn't distinguish between
> > "uniformly poor compression" and "a few completely incompressible pages
> > mixed with highly compressible ones". The zswpraw stat provides direct
> > visibility into the latter case.
>

Actually I forgot - can you also update the Documentation:

Documentation/admin-guide/cgroup-v2.rst

to include a short description of the new counter? Thanks!