linux-kernel - [PATCH v2] mm: memcg/slab: Fix root memcg vmstats

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Message-Id: <20201110031015.15715-1-songmuchun@bytedance.com>
Date:   Tue, 10 Nov 2020 11:10:15 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     hannes@...xchg.org, mhocko@...nel.org, vdavydov.dev@...il.com,
        akpm@...ux-foundation.org, cl@...ux.com, penberg@...nel.org,
        rientjes@...gle.com, iamjoonsoo.kim@....com, shakeelb@...gle.com,
        guro@...com, vbabka@...e.cz, laoar.shao@...il.com,
        songmuchun@...edance.com, chris@...isdown.name
Cc:     linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org
Subject: [PATCH v2] mm: memcg/slab: Fix root memcg vmstats

If we reparent the slab objects to the root memcg, when we free
the slab object, we need to update the per-memcg vmstats to keep
it correct for the root memcg. Now this at least affects the vmstat
of NR_KERNEL_STACK_KB for !CONFIG_VMAP_STACK when the thread stack
size is smaller than the PAGE_SIZE.

Fixes: ec9f02384f60 ("mm: workingset: fix vmstat counters for shadow nodes")
Signed-off-by: Muchun Song <songmuchun@...edance.com>
Acked-by: Roman Gushchin <guro@...com>
---
 v1->v2:
 - Just resend the patch.

 mm/memcontrol.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 2dde734df7d1..bbd40c5af61e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -875,8 +875,13 @@ void __mod_lruvec_kmem_state(void *p, enum node_stat_item idx, int val)
 	rcu_read_lock();
 	memcg = mem_cgroup_from_obj(p);
 
-	/* Untracked pages have no memcg, no lruvec. Update only the node */
-	if (!memcg || memcg == root_mem_cgroup) {
+	/*
+	 * Untracked pages have no memcg, no lruvec. Update only the
+	 * node. If we reparent the slab objects to the root memcg,
+	 * when we free the slab object, we need to update the per-memcg
+	 * vmstats to keep it correct for the root memcg.
+	 */
+	if (!memcg) {
 		__mod_node_page_state(pgdat, idx, val);
 	} else {
 		lruvec = mem_cgroup_lruvec(memcg, pgdat);
-- 
2.20.1