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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1772065540; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=JmXVL4P1e5YTwQCoJlcBCe7K7mA9E+OOkZZvyk9qLts=; b=Lhjlr5lNIb1WKzputRiZytKzU9MeQHWSk4q1xw1k5qiL896YfGek2Sdzhqho2coh5zYVwK RnxLJhH32L0wMqK9OxLzr06DaYUQX0wC8LuLdxStMCyRXI/R/9diYjyztOSbe7Vtfz0jBa IaqPerrY9fRNnappxWNh4jYDE7ocEoM= From: Roman Gushchin To: Michal =?utf-8?Q?Koutn=C3=BD?= Cc: Andrew Morton , Dave Chinner , Qi Zheng , Muchun Song , Jan Kara , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: Do not allocate shrinker info with cgroup.memory=nokmem In-Reply-To: <20260225-cgroup-ml-nokmem-shrinker-v1-1-d703899bdda4@suse.com> ("Michal =?utf-8?Q?Koutn=C3=BD=22's?= message of "Wed, 25 Feb 2026 19:38:44 +0100") References: <20260225-cgroup-ml-nokmem-shrinker-v1-1-d703899bdda4@suse.com> Date: Thu, 26 Feb 2026 00:25:17 +0000 Message-ID: <7ia4ikbknyfm.fsf@castle.c.googlers.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: CA69F40004 X-Stat-Signature: koeezc3hx8da4qdcoqpthmycxru9sy4m X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1772065541-901332 X-HE-Meta: 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 irqQwae+ W17mtxb+SMUK8/tjQZNp3lHeyVtqffpiEOtAmHvEGRONat+z2zBwSfpGZ65w7v8t2ahL6qn8amif6+AOyrqXmFxsZueS3bk6HI/3qiL34DHuy5ywvYhzExUplxxqUBSMngMeR8P8GONgfOSbf1zlvQu9547J4tZjPwULaIqdc/7RB1UVrhboQb2IZXDPkvNwz4+nO4S0DoxMzLqHAGAglAt7isGYrLbEGSM3F Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Michal Koutn=C3=BD writes: > 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 Reviewed-by: Roman Gushchin Thanks!