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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 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="utf-8" Content-Transfer-Encoding: quoted-printable 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 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 Koutn=C3=BD Acked-by: Qi Zheng Reviewed-by: Muchun Song Reviewed-by: Roman Gushchin --- 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 *shrink= er) =20 if (mem_cgroup_disabled()) return -ENOSYS; + if (mem_cgroup_kmem_disabled() && !(shrinker->flags & SHRINKER_NONSLAB)) + return -ENOSYS; =20 mutex_lock(&shrinker_mutex); id =3D idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL); --- base-commit: cd2e103d57e5615f9bb027d772f93b9efd567224 change-id: 20260225-cgroup-ml-nokmem-shrinker-7da42fbcf8f2 Best regards, --=20 Michal Koutn=C3=BD