From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 2C5B23BD635 for ; Tue, 15 Sep 2026 03:51:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789444299; cv=none; b=biLBpMkZxVPTYLoKs7r0WLYwk/fTuW0JMJXPYJ1lz3yQw9ihH+M7/x8+IZxX9y8TnhzunLVQkOgdbUuu65SPNdiLPNQWqdP533naOgeRAhl/9ehxom3zoDXdqLFE65oNMExvN5u2s/PtJoNxrs+D+/kbFOLc9naek7bpQnXynoo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789444299; c=relaxed/simple; bh=imaT4gJGdRBudaPhpTF3fkuf7JXToqPiWslZj5oa40I=; h=Date:To:From:Subject:Message-Id; b=tKjKZDAdMBa2eStfJgY1D1OY2L6fFHRRFdVC/8knd6tWUMQU/Xk/dOa0UJaDwDlGzoF76C+ooWpTTk/Bqu0mtlQYLLk5fcU/MeJEHAoXZfwPtubSqkgr1KO7P6tlXAOl87HMQRPKcww3eKKcTLxMG+j6xsu2jNdklM5Y8u78ht8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=f9ZhreM+; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="f9ZhreM+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A192E1F000FF; Tue, 15 Sep 2026 03:51:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1789444297; bh=o1lAti4AZBrgyM3L4oFzDm/AngsKAPPjI/7Iy20aH9A=; h=Date:To:From:Subject; b=f9ZhreM++bH9DyELl9T9gcv2tR8oQewxugvb6/eRQjiA6BGEZpcuu5eRD9dIVY1f6 JC16BL5I5VC46FL9Wwnw2vNW7ZsVnPrf0fsPSJSi0qsfquU1wBL33fu7++ujyA8ddx gXywc56jR5gq4tcULUcc36NfAd+XO1TeSwxOXJYM= Date: Mon, 14 Sep 2026 20:51:37 -0700 To: mm-commits@vger.kernel.org,yuanchu@google.com,weixugc@google.com,shakeel.butt@linux.dev,mhocko@kernel.org,ljs@kernel.org,kasong@tencent.com,hannes@cmpxchg.org,david@kernel.org,baoquan.he@linux.dev,baohua@kernel.org,axelrasmussen@google.com,baolin.wang@linux.alibaba.com,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-mglru-clear-the-reference-counter-for-rejected-folios.patch added to mm-unstable branch Message-Id: <20260915035137.A192E1F000FF@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm: mglru: clear the reference counter for rejected folios has been added to the -mm mm-unstable branch. Its filename is mm-mglru-clear-the-reference-counter-for-rejected-folios.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mglru-clear-the-reference-counter-for-rejected-folios.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: Baolin Wang Subject: mm: mglru: clear the reference counter for rejected folios Date: Mon, 14 Sep 2026 19:29:22 +0800 As per the comment on LRU_REFS_FLAGS, when accessed folios are promoted to a new generation, LRU_REFS_FLAGS should be cleared so that the reference counter can start over. For folios rejected by shrink_folio_list(), we clear LRU_REFS_FLAGS and set the PG_active flag when lru_gen_folio_seq() would place them in the oldest generation. That's fine. But for rejected folios where lru_gen_folio_seq() returns a generation other than the oldest one (which can be treated as a promotion), we do not clear LRU_REFS_FLAGS. This can violate the promotion mechanism. And this means the rejected folio enters the new generation with stale, inflated tier bits, which can inflate reference counts and distort eviction statistics for these rejected folios. Fix this by clearing LRU_REFS_FLAGS for rejected folios. Of course, I need to evaluate the impact of the changes, which mainly falls into 3 cases: 1. When lru_gen_folio_seq() returns the oldest generation for rejected folios, there are no logic changes, and they will be put back into the 2nd youngest generation. 2. For rejected folios with PG_active set by shrink_folio_list(), we only clear the LRU_REFS_FLAGS and do not change the generation. 3. For rejected folios with PG_referenced set, the original code would put them back into the 2nd oldest generation. After this patch, we will put them back into the 2nd youngest generation. I think case 3 is also reasonable, before commmit 6cbdd9726fb5 ("mm/mglru: use folio_mark_accessed to replace folio_set_active"), a rejected referenced folio was also put back to the 2nd youngest gen. Meanwhile, I didn't see any noticeable performance impact on my 32-core Arm machine when running 'make -j32' to build the kernel inside a 3G-limited memcg with either zram or NVMe swap. Link: https://lore.kernel.org/7384df363c12e4acdaa2e0428420cd8eed320ee7.1789384831.git.baolin.wang@linux.alibaba.com Signed-off-by: Baolin Wang Signed-off-by: Andrew Morton Reviewed-by: Baoquan He Reviewed-by: Kairui Song Reviewed-by: Barry Song Cc: Axel Rasmussen Cc: David Hildenbrand Cc: Johannes Weiner Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Shakeel Butt Cc: Wei Xu Cc: Yuanchu Xie --- mm/vmscan.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) --- a/mm/vmscan.c~mm-mglru-clear-the-reference-counter-for-rejected-folios +++ a/mm/vmscan.c @@ -5072,11 +5072,15 @@ retry: continue; } - /* don't add rejected folios to the oldest generation */ - if (lru_gen_folio_seq(lruvec, folio, false) == min_seq[type]) { - folio_set_lru_refs(folio, 0); + /* + * See the comments on LRU_REFS_FLAGS. + * + * The rejected folios are never added to the oldest generation, + * so this effectively promotes them by at least one generation. + */ + folio_set_lru_refs(folio, 0); + if (lru_gen_folio_seq(lruvec, folio, false) == min_seq[type]) folio_set_active(folio); - } } move_folios_to_lru(&list); _ Patches currently in -mm which might be from baolin.wang@linux.alibaba.com are maintainers-add-baoquan-and-me-as-mglru-reviewers.patch mm-shmem-ignore-sysfs-configs-for-shmem-forced-collapse.patch mm-mglru-clear-the-reference-counter-for-rejected-folios.patch