linux-kernel - Re: [RFC][PATCH] Remove cgroup member from struct page

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Date:	Mon, 01 Sep 2008 13:03:25 +0400
From:	Pavel Emelyanov <xemul@...nvz.org>
To:	Balbir Singh <balbir@...ux.vnet.ibm.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>, hugh@...itas.com,
	kamezawa.hiroyu@...fujitsu.com, menage@...gle.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC][PATCH] Remove cgroup member from struct page

Balbir Singh wrote:
> This is a rewrite of a patch I had written long back to remove struct page
> (I shared the patches with Kamezawa, but never posted them anywhere else).
> I spent the weekend, cleaning them up for 2.6.27-rc5-mmotm (29 Aug 2008).
> 
> I've tested the patches on an x86_64 box, I've run a simple test running
> under the memory control group and the same test running concurrently under
> two different groups (and creating pressure within their groups). I've also
> compiled the patch with CGROUP_MEM_RES_CTLR turned off.
> 
> Advantages of the patch
> 
> 1. It removes the extra pointer in struct page
> 
> Disadvantages
> 
> 1. It adds an additional lock structure to struct page_cgroup
> 2. Radix tree lookup is not an O(1) operation, once the page is known
>    getting to the page_cgroup (pc) is a little more expensive now.

And besides, we also have a global lock, that protects even lookup
from this structure. Won't this affect us too much on bug-smp nodes?

> This is an initial RFC for comments
> 
> TODOs
> 
> 1. Test the page migration changes
> 2. Test the performance impact of the patch/approach
> 
> Comments/Reviews?
> 
> Signed-off-by: Balbir Singh <balbir@...ux.vnet.ibm.com>
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