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[195.250.132.146]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-439dad8da01sm28684927f8f.1.2026.03.09.08.08.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Mar 2026 08:08:28 -0700 (PDT) From: =?utf-8?q?Michal_Koutn=C3=BD?= Date: Mon, 09 Mar 2026 16:08:08 +0100 Subject: [PATCH v2] 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: <20260309-cgroup-ml-nokmem-shrinker-v2-1-3e7a7eefb6c9@suse.com> X-B4-Tracking: v=1; b=H4sIAFfirmkC/42NTQ6CMBBGr0Jm7RgYfwBX3sOwgHYKE2xLWiEaw t2tnMDl+5LvvRUiB+EIt2yFwItE8S4BHTJQQ+t6RtGJgXK65kQXVH3w84T2ic6Pli3GIYgbOWC p2zOZTpnKEKT/FNjIe3c/msSDxJcPnz21FL/1H+tSYIG6zE9VXXc6Je5xjnxU3kKzbdsXp5Wol sEAAAA= 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=2455; i=mkoutny@suse.com; h=from:subject:message-id; bh=PF7PEPuBVFEev9rRlZplgRHqFt2dHhMGKiCN80nPSv0=; b=owGbwMvMwCVWZ8v0fMrtHxyMp9WSGDLXPUo7IhO6X+rd1bAl3syOVw64fv6zKWBh/qo13sXl2 6vcH/y075jIwiDGxWAppsjiJJzHOv+DjJvl6a4vMHNYmUCGSIs0MAABCwNfbmJeqZGOkZ6ptqGe IZChY8TAxSkAU11jzvCH33/risv7sgOdm590TbQulDR4aWJVzntyxapwKVtTtrQ1jAxnmvhWXne JPlO8YcG3+bcyo89Fl7ryq23ZtJlH+uLaR1XMAA== 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. Reviewed-by: Muchun Song Acked-by: Qi Zheng Reviewed-by: Roman Gushchin Signed-off-by: Michal Koutn=C3=BD --- Changes in v2: - update comment (Qi) - collect trailers - rebase on master - Link to v1: https://lore.kernel.org/r/20260225-cgroup-ml-nokmem-shrinker-= v1-1-d703899bdda4@suse.com --- mm/shrinker.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/mm/shrinker.c b/mm/shrinker.c index 7b61fc0ee78fb..167cd70ae4918 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); @@ -716,6 +718,7 @@ struct shrinker *shrinker_alloc(unsigned int flags, con= st char *fmt, ...) * - non-memcg-aware shrinkers * - !CONFIG_MEMCG * - memcg is disabled by kernel command line + * - non-slab shrinkers: when memcg kmem is disabled */ size =3D sizeof(*shrinker->nr_deferred); if (flags & SHRINKER_NUMA_AWARE) --- base-commit: 1f318b96cc84d7c2ab792fcc0bfd42a7ca890681 change-id: 20260225-cgroup-ml-nokmem-shrinker-7da42fbcf8f2 Best regards, --=20 Michal Koutn=C3=BD