linux-kernel - Re: [patch 1/4] mm: memcontrol: uncharge pages on swapout

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Date:	Wed, 22 Oct 2014 17:34:55 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Vladimir Davydov <vdavydov@...allels.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 1/4] mm: memcontrol: uncharge pages on swapout

On Mon 20-10-14 11:22:09, Johannes Weiner wrote:
> mem_cgroup_swapout() is called with exclusive access to the page at
> the end of the page's lifetime.  Instead of clearing the PCG_MEMSW
> flag and deferring the uncharge, just do it right away.  This allows
> follow-up patches to simplify the uncharge code.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

OK, it makes sense. With the irq fixup
Acked-by: Michal Hocko <mhocko@...e.cz>

> ---
>  mm/memcontrol.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index bea3fddb3372..7709f17347f3 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5799,6 +5799,7 @@ static void __init enable_swap_cgroup(void)
>   */
>  void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
>  {
> +	struct mem_cgroup *memcg;
>  	struct page_cgroup *pc;
>  	unsigned short oldid;
>  
> @@ -5815,13 +5816,21 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
>  		return;
>  
>  	VM_BUG_ON_PAGE(!(pc->flags & PCG_MEMSW), page);
> +	memcg = pc->mem_cgroup;
>  
> -	oldid = swap_cgroup_record(entry, mem_cgroup_id(pc->mem_cgroup));
> +	oldid = swap_cgroup_record(entry, mem_cgroup_id(memcg));
>  	VM_BUG_ON_PAGE(oldid, page);
> +	mem_cgroup_swap_statistics(memcg, true);
>  
> -	pc->flags &= ~PCG_MEMSW;
> -	css_get(&pc->mem_cgroup->css);
> -	mem_cgroup_swap_statistics(pc->mem_cgroup, true);
> +	pc->flags = 0;
> +
> +	if (!mem_cgroup_is_root(memcg))
> +		page_counter_uncharge(&memcg->memory, 1);
> +
> +	local_irq_disable();
> +	mem_cgroup_charge_statistics(memcg, page, -1);
> +	memcg_check_events(memcg, page);
> +	local_irq_enable();
>  }
>  
>  /**
> -- 
> 2.1.2
> 

-- 
Michal Hocko
SUSE Labs
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