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

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Date:	Mon, 01 Sep 2008 11:55:39 +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,
	"nickpiggin@...oo.com.au" <nickpiggin@...oo.com.au>
Subject: Re: [RFC][PATCH] Remove cgroup member from struct page

KAMEZAWA Hiroyuki wrote:
> On Mon, 01 Sep 2008 11:39:26 +0530
> Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> 
> 
>>> The development of lockless-page_cgroup is not stalled. I'm just waiting for
>>> my 8cpu box comes back from maintainance...
>>> If you want to see, I'll post v3 with brief result on small (2cpu) box.
>>>
>> I understand and I am not pushing you to completing it, but at the same time I
>> don't want to queue up behind it for long. I suspect the cost of porting
>> lockless page cache on top of my patches should not be high, but I'll never know
>> till I try :)
>>
> My point is, your patch adds big lock. Then, I don't have to do meaningless effort
> to reduce lock.

My patch does not add a big lock, it moves the lock from struct
page->page_cgroup to struct page_cgroup. The other locking added is the locking
overhead associated with inserting entries into the radix tree, true. I ran
oprofile along with lockdep and lockstats enabled on my patches. I don't see the
radix_tree or page_cgroup->lock showing up, I see __slab_free and __slab_alloc
showing up. I'll poke a little further.

Please don't let my patch stop you, we'll integrate the best of both worlds and
what is good for memcg.

-- 
	Balbir
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