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

[Jiayuan Chen]

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


> 
> On Thu, Feb 5, 2026 at 9:31 AM Nhat Pham <nphamcs@xxxxxxxxx> wrote:
> 
> > 
> > On Wed, Feb 4, 2026 at 9:31 PM Jiayuan Chen <jiayuan.chen@xxxxxxxxx> wrote:
> > 
> >  From: Jiayuan Chen <jiayuan.chen@xxxxxxxxxx>
> > 
> >  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.