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

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Date:	Mon, 08 Sep 2008 21:18:37 -0700
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	Nick Piggin <nickpiggin@...oo.com.au>,
	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 Mon, 8 Sep 2008 20:58:10 +0530
> Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
>> Sorry for the delay in sending out the new patch, I am traveling and
>> thus a little less responsive. Here is the update patch
>>
>>
> Hmm.. I've considered this approach for a while and my answer is that
> this is not what you really want.
> 
> Because you just moves the placement of pointer from memmap to
> radix_tree both in GFP_KERNEL, total kernel memory usage is not changed.

Agreed, but we do reduce the sizeof(struct page) without adding on to
page_cgroup's size. So why don't we want this?

> So, at least, you have to add some address calculation (as I did in March)
> to getting address of page_cgroup.

What address calculation do we need, sorry I don't recollect it.

 But page_cgroup itself consumes 32bytes
> per page. Then.....
> 
> My proposal to 32bit system is following 
>  - remove page_cgroup completely.
>    - As a result, there is no per-cgroup lru. But it will not be bad
>      bacause the number of cgroups and pages are not big.
>      just a trade-off between kernel-memory-space v.s. speed.

32 bit systems with PAE can support quite a lot of memory, so I am not sure I
agree. I don't like this approach

>    - Removing page_cgroup and just remember address of mem_cgroup per page.
> 

This is on top of the suggested approach above?

> How do you think ?
> 

I don't like the approach.

-- 
	Balbir
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