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From: Yosry Ahmed To: Jiayuan Chen Cc: linux-mm@kvack.org, Jiayuan Chen , Nhat Pham , Tejun Heo , Johannes Weiner , Michal =?utf-8?Q?Koutn=C3=BD?= , Jonathan Corbet , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Chengming Zhou , Shuah Khan , cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v2 1/2] mm: zswap: add per-memcg stat for incompressible pages Message-ID: References: <20260206072220.144008-1-jiayuan.chen@linux.dev> <20260206072220.144008-2-jiayuan.chen@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260206072220.144008-2-jiayuan.chen@linux.dev> X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 48A0B180011 X-Stat-Signature: b9ketzj5n1wbdp118cupe6idkum586xj X-Rspam-User: X-HE-Tag: 1770391187-772568 X-HE-Meta: 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 AxGet9Ow VTztJumS/1Kgl76d6CeEguA0/9ju/jmuYqYaaJnVg6p/HRr1Ste2L0I/4gHlGjFUUEpPo44g8+vglLUmMY6ha+jIfgbVE+R4LplcR/Y8pAEQNZ/RpbqaLJcF5ylzjQTjYEhYl6pKxDmfVi+obrkoI6JOclX33fsP2rrG6ThWCG+TIQVAyqmsS+o6og4/s+q+Fb9JCQKbJU7fcWls9YzJMUULutHTBsw4RLDVJvbhaKVqGTJXPGQM6UKy6rtdi3rPMRr1/AGrF8+pSBlXyjlqotd7QIPmlQSn+9DVq2qV54VkCUrssAn02uy0O1Q== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Feb 06, 2026 at 03:22:15PM +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 [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. > > [1]: https://lore.kernel.org/linux-mm/CAF8kJuONDFj4NAksaR4j_WyDbNwNGYLmTe-o76rqU17La=nkOw@mail.gmail.com/ > Acked-by: Nhat Pham > Signed-off-by: Jiayuan Chen > --- > Documentation/admin-guide/cgroup-v2.rst | 5 +++++ > include/linux/memcontrol.h | 1 + > mm/memcontrol.c | 8 ++++++++ > 3 files changed, 14 insertions(+) > > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst > index 7f5b59d95fce..78a329414615 100644 > --- a/Documentation/admin-guide/cgroup-v2.rst > +++ b/Documentation/admin-guide/cgroup-v2.rst > @@ -1737,6 +1737,11 @@ The following nested keys are defined. > zswpwb > Number of pages written from zswap to swap. > > + zswap_incomp > + Number of incompressible pages currently stored in zswap > + without compression. These pages could not be compressed to > + a size smaller than PAGE_SIZE, so they are stored as-is. > + > thp_fault_alloc (npn) > Number of transparent hugepages which were allocated to satisfy > a page fault. This counter is not present when CONFIG_TRANSPARENT_HUGEPAGE > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index b6c82c8f73e1..d8ec05dd5d43 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_INCOMP, > MEMCG_NR_STAT, > }; > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 007413a53b45..a6b6cf5f1aeb 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -341,6 +341,7 @@ static const unsigned int memcg_stat_items[] = { > MEMCG_KMEM, > MEMCG_ZSWAP_B, > MEMCG_ZSWAPPED, > + MEMCG_ZSWAP_INCOMP, > }; > > #define NR_MEMCG_NODE_STAT_ITEMS ARRAY_SIZE(memcg_node_stat_items) > @@ -1346,6 +1347,7 @@ static const struct memory_stat memory_stats[] = { > #ifdef CONFIG_ZSWAP > { "zswap", MEMCG_ZSWAP_B }, > { "zswapped", MEMCG_ZSWAPPED }, > + { "zswap_incomp", MEMCG_ZSWAP_INCOMP }, > #endif > { "file_mapped", NR_FILE_MAPPED }, > { "file_dirty", NR_FILE_DIRTY }, > @@ -5458,6 +5460,9 @@ void obj_cgroup_charge_zswap(struct obj_cgroup *objcg, size_t size) > memcg = obj_cgroup_memcg(objcg); > mod_memcg_state(memcg, MEMCG_ZSWAP_B, size); > mod_memcg_state(memcg, MEMCG_ZSWAPPED, 1); > + /* size == PAGE_SIZE means compression failed, page is incompressible */ I think the comment is not very useful, but maybe not worth sending a new version. Otherwise LGTM: Reviewed-by: Yosry Ahmed > + if (size == PAGE_SIZE) > + mod_memcg_state(memcg, MEMCG_ZSWAP_INCOMP, 1); > rcu_read_unlock(); > } > > @@ -5481,6 +5486,9 @@ void obj_cgroup_uncharge_zswap(struct obj_cgroup *objcg, size_t size) > memcg = obj_cgroup_memcg(objcg); > mod_memcg_state(memcg, MEMCG_ZSWAP_B, -size); > mod_memcg_state(memcg, MEMCG_ZSWAPPED, -1); > + /* size == PAGE_SIZE means compression failed, page is incompressible */ > + if (size == PAGE_SIZE) > + mod_memcg_state(memcg, MEMCG_ZSWAP_INCOMP, -1); > rcu_read_unlock(); > } > > -- > 2.43.0 >