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

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Message-Id: <20080926185505.e26d90bf.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 26 Sep 2008 18:55:05 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.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

On Fri, 26 Sep 2008 15:02:13 +0530
Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:

> KAMEZAWA Hiroyuki wrote:
> > On Fri, 26 Sep 2008 13:55:54 +0530
> > Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> > 
> >> 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). 
> > 
> > Because they are not on LRU ...i.e. !PageLRU(page)
> > 
> 
> I understand.. Thanks for clarifying.. my concern is w.r.t accounting, we
> account it in RSS (file RSS).
> 
Yes. Because page->mapping is NULL, there are accounted as RSS.

AFAIK, what bad about !PageLRU(page) is..
1. we skips !PageLRU(page) in force_empty. and we cannot reduce account.
2. we don't know we can trust that page is treated as usual LRU page.

I'll update description.

Thanks,
-Kame





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