From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7063DEF5868 for ; Sun, 15 Feb 2026 07:29:14 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6199C6B0005; Sun, 15 Feb 2026 02:29:13 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 59D836B0088; Sun, 15 Feb 2026 02:29:13 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 49F366B008A; Sun, 15 Feb 2026 02:29:13 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 377386B0005 for ; Sun, 15 Feb 2026 02:29:13 -0500 (EST) Received: from smtpin08.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id C1335140A37 for ; Sun, 15 Feb 2026 07:29:12 +0000 (UTC) X-FDA: 84445864944.08.5C13E52 Received: from out-180.mta0.migadu.com (out-180.mta0.migadu.com [91.218.175.180]) by imf24.hostedemail.com (Postfix) with ESMTP id B7850180004 for ; Sun, 15 Feb 2026 07:29:10 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=ZmYS8zv1; spf=pass (imf24.hostedemail.com: domain of qi.zheng@linux.dev designates 91.218.175.180 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1771140551; h=from:from:sender: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:dkim-signature; bh=GaUSkkuQJofxBHkox8rsl9hWWFEkHV2aAas3PKJ8HkM=; b=YdBYk30CKLHg1q1/epJpDdRPBtOfKVGAEoWyYbMrETW5Kd6Hx19gCHiycT5r8y9L5JZ+dW UmzaNueZlBk9IaiRO1j+boPkA8M1g/USCs5iydjHh5XORPr1RcFr0Aw/JfsgmDu6prbrjD pWRGORBVb29l4028c2Skvv6Gjog/VOU= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=ZmYS8zv1; spf=pass (imf24.hostedemail.com: domain of qi.zheng@linux.dev designates 91.218.175.180 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1771140551; a=rsa-sha256; cv=none; b=bVbQy7YQ+pTE7PCCP6BkMSLP4TYWA61ZMquAaWgQFFWMvvBvF36oW53ZTUrLD9xBaSAouq gE/fFQcspeokrX3UK/oArDOCVJbCMu0U1j02+401FGBPASWVlN5ei4Ukl08/5vq/m+OLnc 3h/jHxe4jHgGyLONjg8J/nzpTLkX0W8= 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 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 X-Stat-Signature: z3apyi1w6bxkqqkb9nnkk9daug5ywnx5 X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: B7850180004 X-HE-Tag: 1771140550-665983 X-HE-Meta: U2FsdGVkX1+ikITX6ptODv6GRJvkpDcJG/ea6Pv0qrpA2REq+zhqLrUeAMskD8F2G4FXcgg7BIU7mmskt0MJYV/c17XNcETb0uI6Vb3gKe5jhziYG4gqpTdn4m/+i9YX7Y1H22YKBPaNsMbSqnfXXIBFU4KOsJtryxXuCYSefPqw16qpQLNM5EzsbYqeviwi+BVbHcnbxABKdt3W/PO1zyFh3GnmYP4KO8Sh6ONtohIFsJ/nXOIxd/UvcOilh+nKQOTokz7r5g+YNr/4OTawRzAv8aqdS5/XPviPnNT+zAotdg3TsYifhuvg7K2+M0L1LVmZ/d+FPBYWwT1sKU3RTh+WNZul3lw3IoimBPpjoXzGSbVdajeyxnSEXjQzfqvYpZyEPuWprp6YRVTG8q1L9kZRnqt9ZZ9pztgtbAh0YKOYUFBqEvfvjdme/IT65RWn2M+5laL11rfLfeG73B/C/K2x2jaKr5QsPMwKq8z2oY/D6f4dotIfRZVdmKiV8iBpTuSDV/jbNyr0kw5IFNjJMAmmXkMfl7qDHiUGDfgYAm0QGDxcboDRaJN9p+o4+blJTx9ahM1wFWPiQsEottM4QZ77fSpxulDVwXuZWnXukqYlNwrDbFI5bzOgv3cEWpnalhaI27oOmL8Ir7gB+Qf3s0NZqUZTetQRvh5nFlhRTumn+A3YP1H6L3ntNTSpkpNf06zWXdjImG9flzq4HcBoUGjYG6WaaiualuDYzWZIh4h11aVeXkeuW+VYsXMTYp1CuOBXRvzZRBFNZ4S9+vuYQIqTohgeOYPONSJuv3d5wZuaTIRYE2lbRh1RCjyELrhUHIALfTedPcpfke0UOZgKRlW/VJG4u9kwygU75JkIXi6fuegGawpzjXME0z/ZpxxfQXzr9bM/rQaJ7KJJ3iDtsBFoA+g5LLQkKndcFV624FQCzLIuPr/70ACaDHX0BDyhTxZGhpkP+EY6ecOYYtT NezLeCbi F+2cu7Usr2E41WWJvKxczdN2X8yeg7FVA3VGFrFGGCScAqIVReybwADW3I5BmNnAIx91vELjhCdTy2sZ5scgMf1q2rkdYxTcMPsccTVRM+mHS/n4ww3bKpqOFDFiu/ORKzGwE1vi5TcalrsW8DJ7OqTRrSRx/aTADugXZs8TK/88puTd3Df49UPvSu63vO3k86CVHeXY7J4rqUxDcOXmChpixyFLMHHNxpxNCpeqHfo5MGxQeb0DVtAEKA9XdJtE5Qqjb X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 */ >