linux-kernel - Re: [PATCH v4] memcg: fix leak on wrong LRU with FUSE

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Message-Id: <20110310150428.f175758c.nishimura@mxp.nes.nec.co.jp>
Date:	Thu, 10 Mar 2011 15:04:28 +0900
From:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Subject: Re: [PATCH v4] memcg: fix leak on wrong LRU with FUSE

On Thu, 10 Mar 2011 14:47:52 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> On Thu, 10 Mar 2011 08:36:59 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> 
> > will add. Thank you !
> > 
> 
> Here is v4 based on feedbacks.
> ==
> 
> fs/fuse/dev.c::fuse_try_move_page() does
> 
>    (1) remove a page by ->steal()
>    (2) re-add the page to page cache 
>    (3) link the page to LRU if it was not on LRU at (1)
> 
> This implies the page is _on_ LRU when it's added to radix-tree.
> So, the page is added to  memory cgroup while it's on LRU and
> the pave will remain in the old(wrong) memcg.
> By this bug, force_empty()'s LRU scan cannot find the page and
> rmdir() will never ends.
> 
> This is the same behavior as SwapCache and needs special care as
>  - remove page from LRU before overwrite pc->mem_cgroup.
>  - add page to LRU after overwrite pc->mem_cgroup.
> 
> This will fixes memcg's rmdir() hang issue with FUSE.
> 
> Changelog v3=v4:
>   - moved PageLRU() check into the leaf function.
>   - added comments
> 
> Changelog v2=>v3:
>   - fixed double accounting.
> 
> Changelog v1=>v2:
>   - clean up.
>   - cover !PageLRU() by pagevec case.
> 
> Reviewed-by: Johannes Weiner <hannes@...xchg.org>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

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

I hope this can fix the original BZ case.

Thanks,
Daisuke Nishimura.
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