linux-kernel - Re: [PATCH 1/4] memcg: account swap cache under lock

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Message-Id: <20080929203307.918e7990.nishimura@mxp.nes.nec.co.jp>
Date:	Mon, 29 Sep 2008 20:33:07 +0900
From:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	nishimura@....nes.nec.co.jp,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"xemul@...nvz.org" <xemul@...nvz.org>
Subject: Re: [PATCH 1/4] memcg: account swap cache under lock

On Mon, 29 Sep 2008 19:21:23 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> While page-cache's charge/uncharge is done under page_lock(), swap-cache
> isn't. (anonymous page is charged when it's newly allocated.)
> 
> This patch moves do_swap_page()'s charge() call under lock.
> I don't see any bad problem *now* but this fix will be good for future
> for avoiding unneccesary racy state.
> 
> 
> Changelog: (v5) -> (v6)
>  - mark_page_accessed() is moved before lock_page().
>  - fixed missing unlock_page()
> (no changes in previous version)
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> 
Looks good to me.

	Reviewed-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>

>  mm/memory.c |   11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> Index: mmotm-2.6.27-rc7+/mm/memory.c
> ===================================================================
> --- mmotm-2.6.27-rc7+.orig/mm/memory.c
> +++ mmotm-2.6.27-rc7+/mm/memory.c
> @@ -2326,16 +2326,17 @@ static int do_swap_page(struct mm_struct
>  		count_vm_event(PGMAJFAULT);
>  	}
>  
> +	mark_page_accessed(page);
> +
> +	lock_page(page);
> +	delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
> +
>  	if (mem_cgroup_charge(page, mm, GFP_KERNEL)) {
> -		delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
>  		ret = VM_FAULT_OOM;
> +		unlock_page(page);
>  		goto out;
>  	}
>  
> -	mark_page_accessed(page);
> -	lock_page(page);
> -	delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
> -
>  	/*
>  	 * Back out if somebody else already faulted in this pte.
>  	 */
> 
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