linux-kernel - Re: [PATCH 1/12] memcg avoid accounting special mappings not on LRU

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Message-ID: <48DC9C92.4000408@linux.vnet.ibm.com>
Date:	Fri, 26 Sep 2008 13:55:54 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"xemul@...nvz.org" <xemul@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Dave Hansen <haveblue@...ibm.com>, ryov@...inux.co.jp
Subject: Re: [PATCH 1/12] memcg avoid accounting special mappings not on LRU

KAMEZAWA Hiroyuki wrote:
> There are not-on-LRU pages which can be mapped and they are not worth to
> be accounted. (becasue we can't shrink them and need dirty codes to handle
> specical case) We'd like to make use of usual objrmap/radix-tree's protcol
> and don't want to account out-of-vm's control pages.
> 
> When special_mapping_fault() is called, page->mapping is tend to be NULL 
> and it's charged as Anonymous page.
> insert_page() also handles some special pages from drivers.
> 
> This patch is for avoiding to account special pages.
> 

Hmm... I am a little concerned that with these changes actual usage will much
more than what we report in memory.usage_in_bytes. Why not move them to
non-reclaimable LRU list as unevictable pages (once those patches go in, we can
push this as well). I suspect the size of special pages is too short to affect
anything or are you seeing something very different?
-- 
	Balbir
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