Re: [PATCH 4/4] mm: memcontrol: fix swap uncharge on cgroup v2
From: Shakeel Butt <hidden>
Date: 2021-02-12 18:58:08
Also in:
linux-mm, lkml
CCing more folks. On Fri, Feb 12, 2021 at 9:14 AM Muchun Song [off-list ref] wrote:
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 <redacted>What's the user visible impact of this change? One impact I can see is that without this patch meminfo's (SwapTotal - SwapFree) is larger than the sum of top level memory.swap.current. This change will reduce that gap. BTW what about per-cpu slots_ret cache? Should we call mem_cgroup_uncharge_swap() before putting in the cache after this change?
quoted hunk ↗ jump to hunk
--- 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