linux-kernel - Re: [PATCH] Cgroup: Fix memory accounting scalability in shrink_page

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Date:	Fri, 20 Jul 2012 15:53:29 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Minchan Kim <minchan@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	"andi.kleen" <andi.kleen@...el.com>, linux-mm <linux-mm@...ck.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Cgroup: Fix memory accounting scalability in
 shrink_page_list

On Thu 19-07-12 16:34:26, Tim Chen wrote:
[...]
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 33dc256..aac5672 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -779,6 +779,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>  
>  	cond_resched();
>  
> +	mem_cgroup_uncharge_start();
>  	while (!list_empty(page_list)) {
>  		enum page_references references;
>  		struct address_space *mapping;

Is this safe? We have a scheduling point few lines below. What prevents
from task move while we are in the middle of the batch?

> @@ -1026,6 +1027,7 @@ keep_lumpy:
>  
>  	list_splice(&ret_pages, page_list);
>  	count_vm_events(PGACTIVATE, pgactivate);
> +	mem_cgroup_uncharge_end();
>  	*ret_nr_dirty += nr_dirty;
>  	*ret_nr_writeback += nr_writeback;
>  	return nr_reclaimed;
> 
> 
> --
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-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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