From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-178.mta0.migadu.com (out-178.mta0.migadu.com [91.218.175.178]) (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 C72DB1862 for ; Sun, 15 Feb 2026 07:29:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771140553; cv=none; b=hHjKqklMrNgBCf34QoHtszop6GDtBex3R9zDJeykFEhuuHm9WV8RwMJtjzbl4xxUKP54Y+s1fVZBAZr9q7LB5q36eYvT3qYDGY84aVyn2kAXdenF5qap29MqwKJOABs34l/uRDmMOVtGQVr1aC0HcS1JjQILQCen1NZRqhloHOk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771140553; c=relaxed/simple; bh=ThZ1j9PUQSBL9DjcFKSrkjuGJ1dYOfl0vsw/9gU+gjs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=EqvXHBHrF34iwi8TOAelwus3BAFFSj5AnKkhsFSGoIU3EgZYkkOUQNqgygt+XbWN5aT9VwyQ9foi+ctNDhDFTK0/FkvKJFq/VXwdp3HDlMCRfLchcO+CIvN94Xdf7m4AHVqurC2WRnib23+uHVKPt+DRNUGVu3jyU70cw7Wfo44= 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=ZmYS8zv1; arc=none smtp.client-ip=91.218.175.178 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="ZmYS8zv1" Message-ID: <5e178b4e-a9e0-44dc-a18d-8c014365ee2f@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1771140548; 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=GaUSkkuQJofxBHkox8rsl9hWWFEkHV2aAas3PKJ8HkM=; b=ZmYS8zv1jl3id/SALH3E1caXqMgXG64D/zHcfOV9yALlFnQAAOgXoaMYN8G6BVHTUFM0Wo eCCHQTErQDaCeHlva3gg/Q2YRDwD8gj1ezn8i0MKmmJIqIOHiO0bB+9VWqySaMbghh0EDo e98G07fXbtM3Un95sSEEVJ4DSdmCX/4= Date: Sun, 15 Feb 2026 15:28:39 +0800 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v4 26/31] mm: vmscan: prepare for reparenting MGLRU folios To: Harry Yoo Cc: hannes@cmpxchg.org, hughd@google.com, mhocko@suse.com, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, david@kernel.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, yosry.ahmed@linux.dev, imran.f.khan@oracle.com, kamalesh.babulal@oracle.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, chenridong@huaweicloud.com, mkoutny@suse.com, akpm@linux-foundation.org, hamzamahfooz@linux.microsoft.com, apais@linux.microsoft.com, lance.yang@linux.dev, bhe@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Qi Zheng References: <2cea0e0cf208e46dc55f2baef8162bedba2db47e.1770279888.git.zhengqi.arch@bytedance.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2/12/26 4:46 PM, Harry Yoo wrote: > On Thu, Feb 05, 2026 at 05:01:45PM +0800, Qi Zheng wrote: >> From: Qi Zheng >> >> Similar to traditional LRU folios, in order to solve the dying memcg >> problem, we also need to reparenting MGLRU folios to the parent memcg when >> memcg offline. >> >> However, there are the following challenges: >> >> 1. Each lruvec has between MIN_NR_GENS and MAX_NR_GENS generations, the >> number of generations of the parent and child memcg may be different, >> so we cannot simply transfer MGLRU folios in the child memcg to the >> parent memcg as we did for traditional LRU folios. >> 2. The generation information is stored in folio->flags, but we cannot >> traverse these folios while holding the lru lock, otherwise it may >> cause softlockup. >> 3. In walk_update_folio(), the gen of folio and corresponding lru size >> may be updated, but the folio is not immediately moved to the >> corresponding lru list. Therefore, there may be folios of different >> generations on an LRU list. >> 4. In lru_gen_del_folio(), the generation to which the folio belongs is >> found based on the generation information in folio->flags, and the >> corresponding LRU size will be updated. Therefore, we need to update >> the lru size correctly during reparenting, otherwise the lru size may >> be updated incorrectly in lru_gen_del_folio(). >> >> Finally, this patch chose a compromise method, which is to splice the lru >> list in the child memcg to the lru list of the same generation in the >> parent memcg during reparenting. And in order to ensure that the parent >> memcg has the same generation, we need to increase the generations in the >> parent memcg to the MAX_NR_GENS before reparenting. >> >> Of course, the same generation has different meanings in the parent and >> child memcg, this will cause confusion in the hot and cold information of >> folios. But other than that, this method is simple enough, the lru size >> is correct, and there is no need to consider some concurrency issues (such >> as lru_gen_del_folio()). >> >> To prepare for the above work, this commit implements the specific >> functions, which will be used during reparenting. >> >> Suggested-by: Harry Yoo >> Suggested-by: Imran Khan >> Signed-off-by: Qi Zheng >> --- >> include/linux/mmzone.h | 16 +++++ >> mm/vmscan.c | 154 +++++++++++++++++++++++++++++++++++++++++ >> 2 files changed, 170 insertions(+) >> >> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h >> index 3e51190a55e4c..0c18b17f0fe2e 100644 >> --- a/include/linux/mmzone.h >> +++ b/include/linux/mmzone.h >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index e2d9ef9a5dedc..8c6f8f0df24b1 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> +void lru_gen_reparent_memcg(struct mem_cgroup *memcg, struct mem_cgroup *parent) >> +{ >> + int nid; >> + >> + for_each_node(nid) { >> + struct lruvec *child_lruvec, *parent_lruvec; >> + int type, zid; >> + struct zone *zone; >> + enum lru_list lru; >> + >> + child_lruvec = get_lruvec(memcg, nid); >> + parent_lruvec = get_lruvec(parent, nid); >> + >> + for_each_managed_zone_pgdat(zone, NODE_DATA(nid), zid, MAX_NR_ZONES - 1) >> + for (type = 0; type < ANON_AND_FILE; type++) >> + __lru_gen_reparent_memcg(child_lruvec, parent_lruvec, zid, type); >> + >> + for_each_lru(lru) { >> + for_each_managed_zone_pgdat(zone, NODE_DATA(nid), zid, MAX_NR_ZONES - 1) { >> + unsigned long size = mem_cgroup_get_zone_lru_size(child_lruvec, lru, zid); >> + >> + mem_cgroup_update_lru_size(parent_lruvec, lru, zid, size); > > This part looks fine, but I think the nr_pages parameter > in mem_cgroup_update_lru_size() should be long instead of int. > Could you please update the type as well? Make sense, and I think it would be better to do this by sending a separate patch, will do that and add your Suggested-by. > > Otherwise looks good to me, > Acked-by: Harry Yoo Thanks! > >> + } >> + } >> + } >> +} >> + >> #endif /* CONFIG_MEMCG */ >