From nobody Mon Feb 9 20:31:48 2026 Received: from out-174.mta0.migadu.com (out-174.mta0.migadu.com [91.218.175.174]) (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 85A3633B973 for ; Tue, 28 Oct 2025 14:03:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.174 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761660224; cv=none; b=fB15HrqTdlW5BoTaViYCHVSQnCCocOP1rexIodshIAuTakSu91yWCYXfm9uFyw6akSLFhNeXFL76tsaf3mtVipith5EdKm1Uzii9DYZh93w5JpscAWfbrVjc8P1dcMyx1TGGsZjc9U/KrU5SiwCOuMjGH792xvazf95OoSNXEoY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761660224; c=relaxed/simple; bh=0WOzV3O7yun4QmZNfkHeGCtNjrtReHHgOdRYuRd4qyA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=TSkH9L5IoObIVKaJFYWtK4ctP8QViyTtuSS9+Cb76kBNopW4Mm55PT7oaOpj/b/cRXtMGip9Gph9KSmq3M/p13cpQnivzEVxmVKu2+8t5kDjZysbtpqA6uB57nTsQcHbrMr4jpxkgbxfKNTp3+KBMj3iw3rgllEq+3wcvQ2JD4w= 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=fhoHKTrq; arc=none smtp.client-ip=91.218.175.174 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="fhoHKTrq" 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=1761660219; 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: in-reply-to:in-reply-to:references:references; bh=wkLnu/O9q4xdyqjaFOUvki0UTYleR0McbTd1ETEhnKE=; b=fhoHKTrqeVk6EZTuFAS26dH7KFQqARavNeR76iE73qBaEIWQbclTIzwrgj8JSL8qtfhWPz Prin+M4U0nQHEyZAfPOwRr6LzXUBd1RKMclEfqJMc+oKdYk9NayqXqvzChMmpi6ZmtuPOL IHh2SSrRo7IPh5r1+4Fh+biiYMfo3io= From: Qi Zheng To: hannes@cmpxchg.org, hughd@google.com, mhocko@suse.com, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, david@redhat.com, lorenzo.stoakes@oracle.com, ziy@nvidia.com, harry.yoo@oracle.com, imran.f.khan@oracle.com, kamalesh.babulal@oracle.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Muchun Song , Qi Zheng Subject: [PATCH v1 13/26] mm: mglru: prevent memory cgroup release in mglru Date: Tue, 28 Oct 2025 21:58:26 +0800 Message-ID: In-Reply-To: References: 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" From: Muchun Song In the near future, a folio will no longer pin its corresponding memory cgroup. To ensure safety, it will only be appropriate to hold the rcu read lock or acquire a reference to the memory cgroup returned by folio_memcg(), thereby preventing it from being released. In the current patch, the rcu read lock is employed to safeguard against the release of the memory cgroup in mglru. This serves as a preparatory measure for the reparenting of the LRU pages. Signed-off-by: Muchun Song Signed-off-by: Qi Zheng --- mm/vmscan.c | 23 +++++++++++++++++------ 1 file changed, 17 insertions(+), 6 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 660cd40cfddd4..676e6270e5b45 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3445,8 +3445,10 @@ static struct folio *get_pfn_folio(unsigned long pfn= , struct mem_cgroup *memcg, if (folio_nid(folio) !=3D pgdat->node_id) return NULL; =20 + rcu_read_lock(); if (folio_memcg(folio) !=3D memcg) - return NULL; + folio =3D NULL; + rcu_read_unlock(); =20 return folio; } @@ -4203,12 +4205,12 @@ bool lru_gen_look_around(struct page_vma_mapped_wal= k *pvmw) unsigned long addr =3D pvmw->address; struct vm_area_struct *vma =3D pvmw->vma; struct folio *folio =3D pfn_folio(pvmw->pfn); - struct mem_cgroup *memcg =3D folio_memcg(folio); + struct mem_cgroup *memcg; struct pglist_data *pgdat =3D folio_pgdat(folio); - struct lruvec *lruvec =3D mem_cgroup_lruvec(memcg, pgdat); - struct lru_gen_mm_state *mm_state =3D get_mm_state(lruvec); - DEFINE_MAX_SEQ(lruvec); - int gen =3D lru_gen_from_seq(max_seq); + struct lruvec *lruvec; + struct lru_gen_mm_state *mm_state; + unsigned long max_seq; + int gen; =20 lockdep_assert_held(pvmw->ptl); VM_WARN_ON_ONCE_FOLIO(folio_test_lru(folio), folio); @@ -4243,6 +4245,13 @@ bool lru_gen_look_around(struct page_vma_mapped_walk= *pvmw) } } =20 + rcu_read_lock(); + memcg =3D folio_memcg(folio); + lruvec =3D mem_cgroup_lruvec(memcg, pgdat); + max_seq =3D READ_ONCE((lruvec)->lrugen.max_seq); + gen =3D lru_gen_from_seq(max_seq); + mm_state =3D get_mm_state(lruvec); + arch_enter_lazy_mmu_mode(); =20 pte -=3D (addr - start) / PAGE_SIZE; @@ -4279,6 +4288,8 @@ bool lru_gen_look_around(struct page_vma_mapped_walk = *pvmw) =20 arch_leave_lazy_mmu_mode(); =20 + rcu_read_unlock(); + /* feedback from rmap walkers to page table walkers */ if (mm_state && suitable_to_scan(i, young)) update_bloom_filter(mm_state, max_seq, pvmw->pmd); --=20 2.20.1