Messages in this thread | | | From | Shakeel Butt <> | Date | Fri, 12 Feb 2021 10:56:54 -0800 | Subject | Re: [PATCH 4/4] mm: memcontrol: fix swap uncharge on cgroup v2 |
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CCing more folks.
On Fri, Feb 12, 2021 at 9:14 AM Muchun Song <songmuchun@bytedance.com> 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 <songmuchun@bytedance.com>
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?
> --- > 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 >
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