From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-188.mta0.migadu.com (out-188.mta0.migadu.com [91.218.175.188]) (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 A937437BE66 for ; Mon, 23 Mar 2026 09:47:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774259274; cv=none; b=FuPpdbIGj9EYAYMPXmpIumuQLPcad/auzhK/lNCQ3RQFoYaCijgL3/8pc1Rs3uelXyEPRw61mRAiyL9lr7Eir9dovOAfh2RGFnGXf4FPyPtGjR725umk3EjeJyCH//MB2v4jmedMPawwBFuxsQuzA9rc1bX+ckfrxneb4/nH73I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774259274; c=relaxed/simple; bh=1nIxTQ8RB+SsqjxPcssgtTJZogdHwXUCrsekegajGP4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=lg8WN9uCJnQ5DIiwPPYdF2iSRT5qFoaA3rEFaXJJO8fO85UfCjBEGcXnO3aLHU5fK1jMjWUYBK+TfU24NHMaerr+qkCRGfmf8aaLooM+C6hkhWp+/ogNHQeLVLtACHzs1PPEHPgWp25o1oy4b67TsMIGC/AicTQ2othpnG9XeF0= 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=CwxYaQu1; arc=none smtp.client-ip=91.218.175.188 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="CwxYaQu1" Message-ID: <2d39ea5e-fd69-4acf-8518-a504f5f7a838@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1774259270; 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=hUcyey8JJET54dG1RcxlUPbktgzb/K1oah1AT7wcgO0=; b=CwxYaQu1n0VmMyb46AU0irJsJRHETzAAsRr3dEl7G8MuKiYiMDYJxB7bCYjztd8Wlyol9Q tvBYS+JsyWstB+h4ToehfXaGvY8XOajahWwp21Dsd6zJj1Oxi8+TUoErpvCTE9LFK/ko7E qunY8dUK2nRfmD6DFG1q6p5QnH6u9h4= Date: Mon, 23 Mar 2026 17:47:27 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v6 30/33] mm: memcontrol: prepare for reparenting non-hierarchical stats To: "Harry Yoo (Oracle)" 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, harry.yoo@oracle.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, usamaarif642@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Qi Zheng , Yosry Ahmed References: 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 Hi Harry, On 3/23/26 3:53 PM, Harry Yoo (Oracle) wrote: > On Thu, Mar 05, 2026 at 07:52:48PM +0800, Qi Zheng wrote: >> From: Qi Zheng >> >> To resolve the dying memcg issue, we need to reparent LRU folios of child >> memcg to its parent memcg. This could cause problems for non-hierarchical >> stats. >> >> As Yosry Ahmed pointed out: >> >> ``` >> In short, if memory is charged to a dying cgroup at the time of >> reparenting, when the memory gets uncharged the stats updates will occur >> at the parent. This will update both hierarchical and non-hierarchical >> stats of the parent, which would corrupt the parent's non-hierarchical >> stats (because those counters were never incremented when the memory was >> charged). >> ``` >> >> Now we have the following two types of non-hierarchical stats, and they >> are only used in CONFIG_MEMCG_V1: >> >> a. memcg->vmstats->state_local[i] >> b. pn->lruvec_stats->state_local[i] >> >> To ensure that these non-hierarchical stats work properly, we need to >> reparent these non-hierarchical stats after reparenting LRU folios. To >> this end, this commit makes the following preparations: >> >> 1. implement reparent_state_local() to reparent non-hierarchical stats >> 2. make css_killed_work_fn() to be called in rcu work, and implement >> get_non_dying_memcg_start() and get_non_dying_memcg_end() to avoid race >> between mod_memcg_state()/mod_memcg_lruvec_state() >> and reparent_state_local() >> >> Co-developed-by: Yosry Ahmed >> Signed-off-by: Yosry Ahmed >> Signed-off-by: Qi Zheng >> Acked-by: Shakeel Butt >> --- >> kernel/cgroup/cgroup.c | 9 ++-- >> mm/memcontrol-v1.c | 16 +++++++ >> mm/memcontrol-v1.h | 7 +++ >> mm/memcontrol.c | 97 ++++++++++++++++++++++++++++++++++++++++++ >> 4 files changed, 125 insertions(+), 4 deletions(-) >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index 23b70bd80ddc9..b0519a16f5684 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -473,6 +501,30 @@ unsigned long lruvec_page_state_local(struct lruvec *lruvec, >> return x; >> } >> >> +#ifdef CONFIG_MEMCG_V1 >> +static void __mod_memcg_lruvec_state(struct mem_cgroup_per_node *pn, >> + enum node_stat_item idx, int val); >> + >> +void reparent_memcg_lruvec_state_local(struct mem_cgroup *memcg, >> + struct mem_cgroup *parent, int idx) >> +{ >> + int nid; >> + >> + for_each_node(nid) { >> + struct lruvec *child_lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid)); >> + struct lruvec *parent_lruvec = mem_cgroup_lruvec(parent, NODE_DATA(nid)); >> + unsigned long value = lruvec_page_state_local(child_lruvec, idx); >> + struct mem_cgroup_per_node *child_pn, *parent_pn; >> + >> + child_pn = container_of(child_lruvec, struct mem_cgroup_per_node, lruvec); >> + parent_pn = container_of(parent_lruvec, struct mem_cgroup_per_node, lruvec); >> + >> + __mod_memcg_lruvec_state(child_pn, idx, -value); >> + __mod_memcg_lruvec_state(parent_pn, idx, value); > > We should probably change the type of `@val` from int to val to avoid > losing non hierarchical stats during reparenting? The parameter and return value of memcg_state_val_in_pages() are both of type int, so perhaps we need a cleanup patch to do this? I will send a cleanup patchset to do this, which includes the following: https://lore.kernel.org/all/5e178b4e-a9e0-44dc-a18d-8c014365ee2f@linux.dev/ Thanks, Qi >