linux-kernel - Re: [PATCH v2 1/2] mm: zswap: add per-memcg stat for incompressible pages

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Message-ID: <20260207012119.69369-1-sj@kernel.org>
Date: Fri,  6 Feb 2026 17:21:18 -0800
From: SeongJae Park <sj@...nel.org>
To: Jiayuan Chen <jiayuan.chen@...ux.dev>
Cc: SeongJae Park <sj@...nel.org>,
	linux-mm@...ck.org,
	Jiayuan Chen <jiayuan.chen@...pee.com>,
	Nhat Pham <nphamcs@...il.com>,
	Tejun Heo <tj@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Koutný <mkoutny@...e.com>,
	Jonathan Corbet <corbet@....net>,
	Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Yosry Ahmed <yosry.ahmed@...ux.dev>,
	Chengming Zhou <chengming.zhou@...ux.dev>,
	Shuah Khan <shuah@...nel.org>,
	cgroups@...r.kernel.org,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 1/2] mm: zswap: add per-memcg stat for incompressible pages

On Fri,  6 Feb 2026 15:22:15 +0800 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 [1].
> 
> Add a new memcg stat 'zswap_incomp' 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 zswap_incomp stat provides
> direct visibility into the latter case.

Sounds like a useful new stat, thank you for making this!

> 
> [1]: https://lore.kernel.org/linux-mm/CAF8kJuONDFj4NAksaR4j_WyDbNwNGYLmTe-o76rqU17La=nkOw@mail.gmail.com/
> Acked-by: Nhat Pham <nphamcs@...il.com>

Nit.  It would look better to have one line before tags lines, or use 'Link:'
tag with '# [1]' like trailing comment for the link.

> Signed-off-by: Jiayuan Chen <jiayuan.chen@...pee.com>

Reviewed-by: SeongJae Park <sj@...nel.org>


Thanks,
SJ

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