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From: Shakeel Butt To: Jiayuan Chen Cc: linux-mm@kvack.org, Jiayuan Chen , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Yosry Ahmed , Nhat Pham , Chengming Zhou , Andrew Morton , Nick Terrell , David Sterba , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v1] mm: zswap: add per-memcg stat for incompressible pages Message-ID: References: <20260205053013.25134-1-jiayuan.chen@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260205053013.25134-1-jiayuan.chen@linux.dev> X-Migadu-Flow: FLOW_OUT On Thu, Feb 05, 2026 at 01:30:12PM +0800, Jiayuan Chen wrote: > From: Jiayuan Chen > > The global zswap_stored_incompressible_pages counter was added in commit > dca4437a5861 ("mm/zswap: store 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. > > Changes > ------- > > 1. Add zswap_is_raw() helper (include/linux/zswap.h) > - Abstract the PAGE_SIZE comparison logic for identifying raw entries > - Keep the incompressible check in one place for maintainability > > 2. Add MEMCG_ZSWAP_RAW stat definition (include/linux/memcontrol.h, > mm/memcontrol.c) > - Add MEMCG_ZSWAP_RAW to memcg_stat_item enum > - Register in memcg_stat_items[] and memory_stats[] arrays > - Export as "zswpraw" in memory.stat > > 3. Update statistics accounting (mm/memcontrol.c, mm/zswap.c) > - Track MEMCG_ZSWAP_RAW in obj_cgroup_charge/uncharge_zswap() > - Use zswap_is_raw() helper in zswap.c for consistency > > Test > ---- > > I wrote a simple test program[1] that allocates memory and compresses it > with zstd, so kernel zswap cannot compress further. > > $ cgcreate -g memory:test > $ cgexec -g memory:test ./test_zswpraw & > $ cat /sys/fs/cgroup/test/memory.stat | grep zswp > zswpraw 0 > zswpin 0 > zswpout 0 > zswpwb 0 > > $ echo "100M" > /sys/fs/cgroup/test/memory.reclaim > $ cat /sys/fs/cgroup/test/memory.stat | grep zswp > zswpraw 104800256 > zswpin 0 > zswpout 51222 > zswpwb 0 > > $ pkill test_zswpraw > $ cat /sys/fs/cgroup/test/memory.stat | grep zswp > zswpraw 0 > zswpin 1 > zswpout 51222 > zswpwb 0 > > [1] https://gist.github.com/mrpre/00432c6154250326994fbeaf62e0e6f1 > > Signed-off-by: Jiayuan Chen Overall looks good but as Nhat suggested please update v2 documentation. > --- > include/linux/memcontrol.h | 1 + > include/linux/zswap.h | 9 +++++++++ > mm/memcontrol.c | 6 ++++++ > mm/zswap.c | 6 +++--- > 4 files changed, 19 insertions(+), 3 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index b6c82c8f73e1..83d1328f81d1 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -39,6 +39,7 @@ enum memcg_stat_item { > MEMCG_KMEM, > MEMCG_ZSWAP_B, > MEMCG_ZSWAPPED, > + MEMCG_ZSWAP_RAW, Hmm I don't like the name though. How about INCOMPRESSIBLE or INCOMP for short?