linux-kernel - [PATCH 4/4] mm: memcontrol: fix swap uncharge on cgroup v2

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Date:   Sat, 13 Feb 2021 01:01:59 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     hannes@...xchg.org, mhocko@...nel.org, vdavydov.dev@...il.com,
        akpm@...ux-foundation.org
Cc:     cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>
Subject: [PATCH 4/4] mm: memcontrol: fix swap uncharge on cgroup v2

The swap charges the actual number of swap entries on cgroup v2.
If a swap cache page is charged successful, and then we uncharge
the swap counter. It is wrong on cgroup v2. Because the swap
entry is not freed.

Fixes: 2d1c498072de ("mm: memcontrol: make swap tracking an integral part of memory control")
Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
 mm/memcontrol.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c737c8f05992..be6bc5044150 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6753,7 +6753,7 @@ int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask)
 	memcg_check_events(memcg, page);
 	local_irq_enable();
 
-	if (PageSwapCache(page)) {
+	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && PageSwapCache(page)) {
 		swp_entry_t entry = { .val = page_private(page) };
 		/*
 		 * The swap entry might not get freed for a long time,
-- 
2.11.0