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b=hGnEWDkMGtKovAsotKqzcJxOtPk7vEtz18C1/IMUcYQzgymgXnYtn/P88DzKkS1C/ 9bg1dZCG9YL6jHVkxvebJbkMXCHR/5ZikFRdC0bZBxN6A1MZzHaqo4e6m0z51R5r94 5QntqB0qAEFSx1N2RVmQTbPNdtBmHjCTPNauPwYev5mEcYTxUHd0XImtli9lne/OHg LVydXzK8oeQWtKHC7IBq8Uow2rx4Nc4Q4W6MjphUTmt2e6zeikJrHKUlAmE2fSFtZr ckU0C98Prp/XpM/CQGb6WbIkph7GraYrtiBP9FauBYnwH9P8cbDiZZuPGi3dPBC6ka 3hizjTu3jMTPw== Date: Tue, 24 Mar 2026 13:05:09 +0900 From: "Harry Yoo (Oracle)" To: Qi Zheng 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, Yosry Ahmed , Qi Zheng Subject: Re: [PATCH v6 30/33] mm: memcontrol: prepare for reparenting non-hierarchical stats Message-ID: References: <2d39ea5e-fd69-4acf-8518-a504f5f7a838@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 720FF140009 X-Stat-Signature: 543e8mwtc9ohcordmwfx3dse1gcedurh X-Rspam-User: X-HE-Tag: 1774325112-55568 X-HE-Meta: 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 24, 2026 at 10:54:48AM +0800, Qi Zheng wrote: > On 3/23/26 8:25 PM, Harry Yoo (Oracle) wrote: > > On Mon, Mar 23, 2026 at 05:47:27PM +0800, Qi Zheng wrote: > > > On 3/23/26 3:53 PM, Harry Yoo (Oracle) wrote: > > > > On Thu, Mar 05, 2026 at 07:52:48PM +0800, Qi Zheng wrote: > > > > > 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? > > > > Yes! > > > > and @val in memcg_rstat_updated() too, I think. > > Right. > > > > > > 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! > > > > Should that ideally be applied before this patchset? > > This would conflict with the current patchset. Right. > The v6 has been in mm-unstable for some time Right. > so I prefer to add a cleanup patchset to > avoid interfering with the merge of this patchset. but it's a little bit more than a cleanup, no? I'd say without the followup, this patchset introduces a very subtle (likely nobody would notice) functional regression visible on memcgs with billions of pages. > Otherwise, sending v7 might be more appropriate. I think it should be sent either as v7 or as part of v7.1-rcX. (Whichever way Andrew prefers) -- Cheers, Harry / Hyeonggon