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From: Shakeel Butt To: Yosry Ahmed Cc: Qi Zheng , hannes@cmpxchg.org, hughd@google.com, mhocko@suse.com, roman.gushchin@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 Subject: Re: [PATCH v5 29/32] mm: memcontrol: prepare for reparenting non-hierarchical stats Message-ID: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT On Wed, Feb 25, 2026 at 06:58:59AM -0800, Yosry Ahmed wrote: > > @@ -473,6 +493,29 @@ unsigned long lruvec_page_state_local(struct lruvec *lruvec, > > return x; > > } > > > > +#ifdef CONFIG_MEMCG_V1 > > +void reparent_memcg_lruvec_state_local(struct mem_cgroup *memcg, > > + struct mem_cgroup *parent, int idx) > > +{ > > + int i = memcg_stats_index(idx); > > + int nid; > > + > > + if (WARN_ONCE(BAD_STAT_IDX(i), "%s: missing stat item %d\n", __func__, idx)) > > + return; > > + > > + 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)); > > + struct mem_cgroup_per_node *parent_pn; > > + unsigned long value = lruvec_page_state_local(child_lruvec, idx); > > + > > + parent_pn = container_of(parent_lruvec, struct mem_cgroup_per_node, lruvec); > > + > > + atomic_long_add(value, &(parent_pn->lruvec_stats->state_local[i])); > > + } > > +} > > Did you measure the impact of making state_local atomic on the flush > path? It's a slow path but we've seen pain from it being too slow > before, because it extends the critical section of the rstat flush > lock. Qi, please measure the impact on flushing and if no impact then no need to do anything as I don't want anymore churn in this series. > > Can we keep this non-atomic and use mod_memcg_lruvec_state() here? It > will update the stat on the local counter and it will be added to > state_local in the flush path when needed. We can even force another > flush in reparent_state_local () after reparenting is completed, if we > want to avoid leaving a potentially large stat update pending, as it > can be missed by mem_cgroup_flush_stats_ratelimited(). > > Same for reparent_memcg_state_local(), we can probably use mod_memcg_state()? Yosry, do you mind sending the patch you are thinking about over this series?