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b=Bk2jSRTQ7fnmwvmvb7lXbQLA03HtBYzQpEBdKc1xSYXE1/nThiPnvYFoADxoWiUi5 S4ckrO0mjLz33wsYhur/G6UTqNR5VSVgytQEl+tecSnJVSW9oIiRNGQiV81CWRDtKw EUQsfK4sLApZyXkfpOt0CcZRvFHuZoy/XLKag6hkzGucXq0RHXe2bMMhd0FycimYa/ s7xKeMGAUhQvAoZ8+BHXSvjiN1u6VEnHJChj1UcMw75qyB3pihi5XOEu6vuzcQwf5Y V5wcfz1HaexVvXzmKWyMRq70V0P1XvnB9j4x2YCM+0g7zvGpGFOGOZ9tc0/L4KqZBG OzrAGp5ykz0ng== From: SeongJae Park To: Jiayuan Chen Cc: SeongJae Park , linux-mm@kvack.org, Jiayuan Chen , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , 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 Date: Thu, 5 Feb 2026 18:21:51 -0800 Message-ID: <20260206022152.67992-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260205053013.25134-1-jiayuan.chen@linux.dev> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: E9A284000E X-Stat-Signature: ncfa77jgwju431rxohgfrh49c3ngfzdn X-Rspam-User: X-HE-Tag: 1770344515-688313 X-HE-Meta: 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 gwkJS2aF LvuIxaAtdid8jKmiwiIzliApZBqP4Nyn6WTgt7LXqtli925ajWXOJtshhcxp9dhVS2Ewj4JqAVwzw7f5M5BiIU0jP5F7than/7Wj2XrP8w441BjRdx+oRO3EsNjxueAu952Ry0WyfzJZGMuFqniAGxEox4pzn+ovUXpJ1N47Ibz+1JZKOpa7ijiuyb/tpuP21ENM5H79MZKAN7fnIjJn70HkdpfL0NpwCVymSvKUUs0z68liD6M1dQtWxWJfMOkx3L/pmI0u0L1zr+/ke64j62Kro19v+nI7AC4F/ 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 Thu, 5 Feb 2026 13:30:12 +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 > --- > 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(-) As others also mentioned, the documentation of the new stat would be needed. > > 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, > MEMCG_NR_STAT, > }; > > diff --git a/include/linux/zswap.h b/include/linux/zswap.h > index 30c193a1207e..94f84b154b71 100644 > --- a/include/linux/zswap.h > +++ b/include/linux/zswap.h > @@ -7,6 +7,15 @@ > > struct lruvec; > > +/* > + * Check if a zswap entry is stored in raw (uncompressed) form. > + * This happens when compression doesn't reduce the size. > + */ > +static inline bool zswap_is_raw(size_t size) > +{ > + return size == PAGE_SIZE; > +} > + No strong opinion, but I'm not really sure if the helper is needed, because it feels quite simple logic: "If an object is compressed and the size is same to the original one, the object is incompressible." I also feel the function name bit odd, given the type of the parameter. Based on the function name and the comment, I'd expect it to receive a zswap_entry object. I understand it is better to receive a size_t, to be called from obj_cgroup_[un]charge_zswap(), though. Even in the case, I think the name can be better (e.g., zswap_compression_failed() or zswap_was_incompressible() ?), or at least the coment can be more kindly explain the fact that the parameter is the size of object after the compression attempt. > extern atomic_long_t zswap_stored_pages; > > #ifdef CONFIG_ZSWAP > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 007413a53b45..32fb801530a3 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_RAW, > }; No strong opinion, but I think Shakeel's suggestion of other names is reasonable. > > #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 }, > + { "zswpraw", MEMCG_ZSWAP_RAW }, Ditto. > #endif > { "file_mapped", NR_FILE_MAPPED }, > { "file_dirty", NR_FILE_DIRTY }, > @@ -5458,6 +5460,8 @@ 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); > + if (zswap_is_raw(size)) > + mod_memcg_state(memcg, MEMCG_ZSWAP_RAW, 1); I understand the helper function is better to receive size_t rather than zswap_entry for this. > rcu_read_unlock(); > } > > @@ -5481,6 +5485,8 @@ 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); > + if (zswap_is_raw(size)) > + mod_memcg_state(memcg, MEMCG_ZSWAP_RAW, -1); > rcu_read_unlock(); > } > > diff --git a/mm/zswap.c b/mm/zswap.c > index 3d2d59ac3f9c..54ab4d126f64 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -723,7 +723,7 @@ static void zswap_entry_free(struct zswap_entry *entry) > obj_cgroup_uncharge_zswap(entry->objcg, entry->length); > obj_cgroup_put(entry->objcg); > } > - if (entry->length == PAGE_SIZE) > + if (zswap_is_raw(entry->length)) > atomic_long_dec(&zswap_stored_incompressible_pages); > zswap_entry_cache_free(entry); > atomic_long_dec(&zswap_stored_pages); > @@ -941,7 +941,7 @@ static bool zswap_decompress(struct zswap_entry *entry, struct folio *folio) > zs_obj_read_sg_begin(pool->zs_pool, entry->handle, input, entry->length); > > /* zswap entries of length PAGE_SIZE are not compressed. */ > - if (entry->length == PAGE_SIZE) { > + if (zswap_is_raw(entry->length)) { > WARN_ON_ONCE(input->length != PAGE_SIZE); > memcpy_from_sglist(kmap_local_folio(folio, 0), input, 0, PAGE_SIZE); > dlen = PAGE_SIZE; Below this part, I show 'dlen == PAGE_SIZE'. Should it also be converted to use the helper function? > @@ -1448,7 +1448,7 @@ static bool zswap_store_page(struct page *page, > obj_cgroup_charge_zswap(objcg, entry->length); > } > atomic_long_inc(&zswap_stored_pages); > - if (entry->length == PAGE_SIZE) > + if (zswap_is_raw(entry->length)) > atomic_long_inc(&zswap_stored_incompressible_pages); > > /* > -- > 2.43.0 Looks good to me overall, though. Thank you for this patch. Thanks, SJ