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[195.250.132.146]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-483bfb29715sm44245515e9.0.2026.02.25.10.39.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Feb 2026 10:39:07 -0800 (PST) From: =?utf-8?q?Michal_Koutn=C3=BD?= Date: Wed, 25 Feb 2026 19:38:44 +0100 Subject: [PATCH] mm: Do not allocate shrinker info with cgroup.memory=nokmem MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Message-Id: <20260225-cgroup-ml-nokmem-shrinker-v1-1-d703899bdda4@suse.com> X-B4-Tracking: v=1; b=H4sIALNBn2kC/x3MTQqEMAxA4atI1hNwgn94lWEWtaYatK2kKIJ4d 4vLb/HeBYlVOEFfXKB8SJIYMr6fAuxswsQoYzZQSU1JVKOdNO4b+hVDXDx7TLNKWFixHU1FbrC ucwS535SdnO/797/vBzJkrwFrAAAA X-Change-ID: 20260225-cgroup-ml-nokmem-shrinker-7da42fbcf8f2 To: Andrew Morton , Dave Chinner , Qi Zheng , Roman Gushchin , Muchun Song Cc: Jan Kara , linux-mm@kvack.org, linux-kernel@vger.kernel.org, =?utf-8?q?Michal_Koutn=C3=BD?= X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=openpgp-sha256; l=1767; i=mkoutny@suse.com; h=from:subject:message-id; bh=vCSUMFDcCR7TTirWzMfGTpmIOE4hV1UFUHSUFG9Fiow=; b=owGbwMvMwCVWZ8v0fMrtHxyMp9WSGDLnOx47cJpF7FzoCh7ZH/MTFX49nTiD4+ACtpjANM83o c+qNM3NOyayMIhxMViKKbI4Ceexzv8g42Z5uusLzBxWJpAh0iINDEDAwsCXm5hXaqRjpGeqbahn aKgDZDJwcQrAVP/5xfBX8KBMyIaes4ce8EefZ7QMiq/1dDNOqkzT2npLLarsUNBVRoZHXGqLOY0 qGa3zGt5qXZD1NUq55Tn/m495SPwJvZnKq5kB X-Developer-Key: i=mkoutny@suse.com; a=openpgp; fpr=9F2AB6F1F2BBEE7621C1B620CFDED9A2FD1314F0 X-Rspam-User: X-Stat-Signature: ua7ewtzetat5zxbg8j8y96mjwtt3ms1h X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: E119B20013 X-HE-Tag: 1772044749-784274 X-HE-Meta: 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 /uIYi56d mS2oFOQPn4lyI5KL+whfms4jac7ySzcH1CoDbcP28DwwFqa88/yqJjQgMa42JV3fPbpU28wD7gR/pNdIrI2kWZ8oW7/iHhvQvc34Vk22FANIDaz3snCWY/w3ThVXrmvMo6Sxim/qpLPL3xwgEiq8CnHueabLwzcr7RSunyU4vwWNUVEVzhFt5WkKwf4eWiqT50kvc2jM6g1EWTVTrAi8lMpCT6iutzGAAE4HRusWefT2CjLj90t1brmQNiU6lRdsKdLetWSGi70x5BgTSpes/NXKo7T8r3qPc5eajJTtaFgvY1vnJifXArxiggGdtBsPYgBPSOSpSyoF0g4FqbZ1W+zW7q2E/6nsR+lhJ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: There'd be no work for memcg-aware shrinkers when kernel memory is not accounted per cgroup, so we can skip allocating per memcg shrinker data. This saves some memory, avoids holding shrinker_mutex with O(nr_memcgs) and saves work in shrink_slab_memcg(). Then there are SHRINKER_NONSLAB shrinkers which handle non-kernel memory so nokmem should not disable their per-memcg behavior. Such shrinkers (e.g. deferred_split_shrinker) still need access to per-memcg data (see also commit 0a432dcbeb32e ("mm: shrinker: make shrinker not depend on memcg kmem")). The savings with this patch come on container hosts that create many superblocks (each with own shrinker) but tracking and processing per-memcg data is pointless with nokmem (shrink_slab_memcg() is partially guarded with !memcg_kmem_online already). The patch uses "boottime" predicate mem_cgroup_kmem_disabled() (not memcg_kmem_online()) to avoid mistakenly un-MEMCG_AWARE-ing shrinkers registered before first non-root memcg is mkdir'd. Signed-off-by: Michal Koutný --- mm/shrinker.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/shrinker.c b/mm/shrinker.c index 4a93fd433689a..7d7302619b7f7 100644 --- a/mm/shrinker.c +++ b/mm/shrinker.c @@ -219,6 +219,8 @@ static int shrinker_memcg_alloc(struct shrinker *shrinker) if (mem_cgroup_disabled()) return -ENOSYS; + if (mem_cgroup_kmem_disabled() && !(shrinker->flags & SHRINKER_NONSLAB)) + return -ENOSYS; mutex_lock(&shrinker_mutex); id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL); --- base-commit: cd2e103d57e5615f9bb027d772f93b9efd567224 change-id: 20260225-cgroup-ml-nokmem-shrinker-7da42fbcf8f2 Best regards, -- Michal Koutný