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

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Message-ID: <bc96ed3734ef03d4defc9c3940893eba8beaf0d9@linux.dev>
Date: Fri, 06 Feb 2026 02:04:16 +0000
From: "Jiayuan Chen" <jiayuan.chen@...ux.dev>
To: "Nhat Pham" <nphamcs@...il.com>
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

February 6, 2026 at 01:45, "Nhat Pham" <nphamcs@...il.com mailto:nphamcs@...il.com?to=%22Nhat%20Pham%22%20%3Cnphamcs%40gmail.com%3E > wrote:


> 
> 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!
>

Thanks Nhat for the review and Acked-by!

I'll update the documentation and add Chris Li's link to
changelog in v2. Will consider the selftest as a follow-up.