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

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Message-ID: <48BCECB5.8070107@linux.vnet.ibm.com>
Date:	Tue, 02 Sep 2008 13:05:17 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Pavel Emelyanov <xemul@...nvz.org>,
	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

Peter Zijlstra wrote:
> On Mon, 2008-09-01 at 14:47 +0530, 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).
> 
> Or you could have a look at the concurrent radix tree, esp for dense
> trees it can save a lot on lock bouncing.
> 
> Latest code available at:
> 
> http://programming.kicks-ass.net/kernel-patches/concurrent-pagecache/27-rc3/

I'll try them later. I see a lot of slab allocations/frees (expected). I am
trying to experiment with alternatives to reduce them.

-- 
	Balbir
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