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

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Message-ID: <48BBB936.5040002@openvz.org>
Date:	Mon, 01 Sep 2008 13:43:18 +0400
From:	Pavel Emelyanov <xemul@...nvz.org>
To:	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:
> Pavel Emelyanov wrote:
>> 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?
> 
> Sorry, not sure I understand. The lookup is done under RCU. Updates are done
> using the global lock. It should not be hard to make the radix tree per node
> later (as an iterative refinement).
> 

OOPS, indeed. Sorry for the confusion, then. :)
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