From nobody Thu Oct 2 03:30:39 2025 Received: from out-170.mta1.migadu.com (out-170.mta1.migadu.com [95.215.58.170]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9A00B284B33 for ; Mon, 22 Sep 2025 22:02:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.170 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758578551; cv=none; b=jpDBs3lVXV7W5HuHRBxEZRk77puvnUCY7o0AoCUgmZyN1dn1UP9lhSjvmtguUsOSLE7elvIthVtIXnmxPv0Vn+aQmMJp1ebSznPJu6KK2tE/H0zjsiazmvfRIWKwbBuISHYt4vdveW4aojnNULUR5X9HIFHT19R0kw6FJdlvrLM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758578551; c=relaxed/simple; bh=LWWy1NSMrdokOxRy9TWCPxhDNVSdaHvZSyTj7oBWRf8=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=jTwFHfnynLO+WGjmmTPgUDoCdJUJNakCFLLA0TViO/VOOjWUGj2f2Ks6raUuH7XOHXg2A/dAkOVW/TYgwubtRH5VNSA0eq359zvun+DxVlPNWd1TKk7gGuyfdzcxnhWa34ACAupQBTIDdqx8BN0LH8YjiQfnzttS6vcxpSg1Cdo= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=ZIesPBQ0; arc=none smtp.client-ip=95.215.58.170 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="ZIesPBQ0" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1758578536; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=LvQMnsu791EG1tpjwy9I3544++reF65dwLMnGRELwws=; b=ZIesPBQ0zAl1Vmukqxmtt0XIK/MVh1ffyqQa8stAcXpFk9CsnyvK3u7hKV5bkDVd50Tz9d 518QauXNlAT2j4sE8owNxzkvVG0kvid9zfQUuEIbqqYr7Or6i+wsuhQ7AAQ3ymIsoYuF80 BhhlByeyTe56tg6TFdwmWHKUtJCGNNw= From: Shakeel Butt To: Andrew Morton Cc: Tejun Heo , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Alexei Starovoitov , Peilin Ye , Kumar Kartikeya Dwivedi , bpf@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team , Michal Hocko Subject: [PATCH v2] memcg: skip cgroup_file_notify if spinning is not allowed Date: Mon, 22 Sep 2025 15:02:03 -0700 Message-ID: <20250922220203.261714-1-shakeel.butt@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset="utf-8" Generally memcg charging is allowed from all the contexts including NMI where even spinning on spinlock can cause locking issues. However one call chain was missed during the addition of memcg charging from any context support. That is try_charge_memcg() -> memcg_memory_event() -> cgroup_file_notify(). The possible function call tree under cgroup_file_notify() can acquire many different spin locks in spinning mode. Some of them are cgroup_file_kn_lock, kernfs_notify_lock, pool_workqeue's lock. So, let's just skip cgroup_file_notify() from memcg charging if the context does not allow spinning. Alternative approach was also explored where instead of skipping cgroup_file_notify(), we defer the memcg event processing to irq_work [1]. However it adds complexity and it was decided to keep things simple until we need more memcg events with !allow_spinning requirement. Link: https://lore.kernel.org/all/5qi2llyzf7gklncflo6gxoozljbm4h3tpnuv4u4ej= 4ztysvi6f@x44v7nz2wdzd/ [1] Signed-off-by: Shakeel Butt Acked-by: Michal Hocko --- Changes since v1: - Add warning if !allow_spinning is used with memcg events other than MEMCG_MAX (requested by Roman) include/linux/memcontrol.h | 26 +++++++++++++++++++------- mm/memcontrol.c | 7 ++++--- 2 files changed, 23 insertions(+), 10 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 16fe0306e50e..873e510d6f8d 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -1001,22 +1001,28 @@ static inline void count_memcg_event_mm(struct mm_s= truct *mm, count_memcg_events_mm(mm, idx, 1); } =20 -static inline void memcg_memory_event(struct mem_cgroup *memcg, - enum memcg_memory_event event) +static inline void __memcg_memory_event(struct mem_cgroup *memcg, + enum memcg_memory_event event, + bool allow_spinning) { bool swap_event =3D event =3D=3D MEMCG_SWAP_HIGH || event =3D=3D MEMCG_SW= AP_MAX || event =3D=3D MEMCG_SWAP_FAIL; =20 + /* For now only MEMCG_MAX can happen with !allow_spinning context. */ + VM_WARN_ON_ONCE(!allow_spinning && event !=3D MEMCG_MAX); + atomic_long_inc(&memcg->memory_events_local[event]); - if (!swap_event) + if (!swap_event && allow_spinning) cgroup_file_notify(&memcg->events_local_file); =20 do { atomic_long_inc(&memcg->memory_events[event]); - if (swap_event) - cgroup_file_notify(&memcg->swap_events_file); - else - cgroup_file_notify(&memcg->events_file); + if (allow_spinning) { + if (swap_event) + cgroup_file_notify(&memcg->swap_events_file); + else + cgroup_file_notify(&memcg->events_file); + } =20 if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) break; @@ -1026,6 +1032,12 @@ static inline void memcg_memory_event(struct mem_cgr= oup *memcg, !mem_cgroup_is_root(memcg)); } =20 +static inline void memcg_memory_event(struct mem_cgroup *memcg, + enum memcg_memory_event event) +{ + __memcg_memory_event(memcg, event, true); +} + static inline void memcg_memory_event_mm(struct mm_struct *mm, enum memcg_memory_event event) { diff --git a/mm/memcontrol.c b/mm/memcontrol.c index e090f29eb03b..4deda33625f4 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2307,12 +2307,13 @@ static int try_charge_memcg(struct mem_cgroup *memc= g, gfp_t gfp_mask, bool drained =3D false; bool raised_max_event =3D false; unsigned long pflags; + bool allow_spinning =3D gfpflags_allow_spinning(gfp_mask); =20 retry: if (consume_stock(memcg, nr_pages)) return 0; =20 - if (!gfpflags_allow_spinning(gfp_mask)) + if (!allow_spinning) /* Avoid the refill and flush of the older stock */ batch =3D nr_pages; =20 @@ -2348,7 +2349,7 @@ static int try_charge_memcg(struct mem_cgroup *memcg,= gfp_t gfp_mask, if (!gfpflags_allow_blocking(gfp_mask)) goto nomem; =20 - memcg_memory_event(mem_over_limit, MEMCG_MAX); + __memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning); raised_max_event =3D true; =20 psi_memstall_enter(&pflags); @@ -2415,7 +2416,7 @@ static int try_charge_memcg(struct mem_cgroup *memcg,= gfp_t gfp_mask, * a MEMCG_MAX event. */ if (!raised_max_event) - memcg_memory_event(mem_over_limit, MEMCG_MAX); + __memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning); =20 /* * The allocation either can't fail or will lead to more memory --=20 2.47.3