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From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"balbir@linux.vnet.ibm.com" <balbir@linux.vnet.ibm.com>,
	hugh@veritas.com, taka@valinux.co.jp
Subject: Re: [RFC][PATCH 2/5] memcg : handle swap cache
Date: Tue, 4 Nov 2008 18:04:29 +0900	[thread overview]
Message-ID: <20081104180429.4e47875e.kamezawa.hiroyu@jp.fujitsu.com> (raw)
In-Reply-To: <20081104174201.9e2dc44c.nishimura@mxp.nes.nec.co.jp>

On Tue, 4 Nov 2008 17:42:01 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> > +#ifdef CONFIG_SWAP
> > +int mem_cgroup_cache_charge_swapin(struct page *page,
> > +			struct mm_struct *mm, gfp_t mask)
> > +{
> > +	int ret = 0;
> > +
> > +	if (mem_cgroup_subsys.disabled)
> > +		return 0;
> > +	if (unlikely(!mm))
> > +		mm = &init_mm;
> > +
> > +	ret = mem_cgroup_charge_common(page, mm, mask,
> > +			MEM_CGROUP_CHARGE_TYPE_SHMEM, NULL);
> > +	/*
> > +	 * The page may be dropped from SwapCache because we don't have
> > +	 * lock_page().This may cause charge-after-uncharge trouble.
> > +	 * Fix it up here. (the caller have refcnt to this page and
> > +	 * page itself is guaranteed not to be freed.)
> > +	 */
> > +	if (ret && !PageSwapCache(page))
> > +		mem_cgroup_uncharge_swapcache(page);
> > +
> Hmm.. after [5/5], mem_cgroup_cache_charge_swapin has 'locked' parameter,
> calls lock_page(if !locked), and checks PageSwapCache under page lock.
> 
> Why not doing it in this patch?
> 

My intention is to guard swap_cgroup by lock_page() against SwapCache.
In Mem+Swap controller. we get "memcg" from information in page->private.
I think we need lock_page(), there. 

But here, we don't refer page->private information. 
I think we don't need lock_page() because there is no inofrmation we depends on.

Thanks,
-Kame


  reply	other threads:[~2008-11-04  9:05 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-10-31  2:50 [RFC][PATCH 0/5] memcg : some patches related to swap KAMEZAWA Hiroyuki
2008-10-31  2:52 ` [RFC][PATCH 1/5] memcg : force_empty to do move account KAMEZAWA Hiroyuki
2008-10-31  9:25   ` Daisuke Nishimura
2008-11-04  6:15   ` Paul Menage
2008-11-04  6:17     ` KAMEZAWA Hiroyuki
2008-11-04  6:23       ` Paul Menage
2008-11-04  6:25         ` KAMEZAWA Hiroyuki
2008-10-31  2:54 ` [RFC][PATCH 2/5] memcg : handle swap cache KAMEZAWA Hiroyuki
2008-11-04  8:42   ` Daisuke Nishimura
2008-11-04  9:04     ` KAMEZAWA Hiroyuki [this message]
2008-11-04 10:28       ` Daisuke Nishimura
2008-11-05  0:07         ` KAMEZAWA Hiroyuki
2008-11-05  2:03           ` KAMEZAWA Hiroyuki
2008-10-31  2:55 ` [RFC][PATCH 3/5] memcg : mem+swap controller kconfig KAMEZAWA Hiroyuki
2008-11-04  8:54   ` Daisuke Nishimura
2008-11-04  9:13     ` KAMEZAWA Hiroyuki
2008-10-31  2:58 ` [RFC][PATCH 4/5] memcg : add swap_cgroup KAMEZAWA Hiroyuki
2008-10-31  2:59 ` [RFC][PATCH 5/5] memcg : mem+swap controller KAMEZAWA Hiroyuki
2008-11-02  6:43 ` [RFC][PATCH 6/5] memcg : synchronous LRU KAMEZAWA Hiroyuki

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