linux-kernel - [PATCH 5.9 251/252] mm: memcg/slab: fix root memcg vmstats

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Message-Id: <20201123121847.702480600@linuxfoundation.org>
Date:   Mon, 23 Nov 2020 13:23:21 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Muchun Song <songmuchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Roman Gushchin <guro@...com>,
        Johannes Weiner <hannes@...xchg.org>,
        David Rientjes <rientjes@...gle.com>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Christopher Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Yafang Shao <laoar.shao@...il.com>,
        Chris Down <chris@...isdown.name>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.9 251/252] mm: memcg/slab: fix root memcg vmstats

From: Muchun Song <songmuchun@...edance.com>

commit 8faeb1ffd79593c9cd8a2a80ecdda371e3b826cb upstream.

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.

David said:
 "I assume that without this fix that the root memcg's vmstat would
  always be inflated if we reparented"

Fixes: ec9f02384f60 ("mm: workingset: fix vmstat counters for shadow nodes")
Signed-off-by: Muchun Song <songmuchun@...edance.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Reviewed-by: Shakeel Butt <shakeelb@...gle.com>
Acked-by: Roman Gushchin <guro@...com>
Acked-by: Johannes Weiner <hannes@...xchg.org>
Acked-by: David Rientjes <rientjes@...gle.com>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Vladimir Davydov <vdavydov.dev@...il.com>
Cc: Christopher Lameter <cl@...ux.com>
Cc: Pekka Enberg <penberg@...nel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
Cc: Roman Gushchin <guro@...com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Yafang Shao <laoar.shao@...il.com>
Cc: Chris Down <chris@...isdown.name>
Cc: <stable@...r.kernel.org>	[5.3+]
Link: https://lkml.kernel.org/r/20201110031015.15715-1-songmuchun@bytedance.com
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -872,8 +872,13 @@ void __mod_lruvec_slab_state(void *p, en
 	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);