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

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Date:	Mon, 01 Sep 2008 09:12:45 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>, hugh@...itas.com,
	menage@...gle.com, xemul@...nvz.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [RFC][PATCH] Remove cgroup member from struct page

KAMEZAWA Hiroyuki wrote:
> On Sun, 31 Aug 2008 23:17:56 +0530
> Balbir Singh <balbir@...ux.vnet.ibm.com> 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.
>>
>> 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?
>>
> BTW, how deep this radix-tree on 4GB/32GB/64GB/256GB machine ?

Good Question,

My ball-park estimates are

number of pfns = RADIX_TREE_TAG_LONGS/(RADIX_TREE_TAG_LONGS - 1) *
(RADIX_TREE_LONGS^n - 1)

and "n" is the number we are looking for.

For a 64 bit system with 256 GB and 4KB page size, I've calculated it to be 9
levels deep.

-- 
	Balbir
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