linux-kernel - Re: [PATCH 2/3] mm, slub: count freed pages via rcu as this task's reclaimed

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Date:	Wed, 10 Apr 2013 11:20:10 +0800
From:	Simon Jeons <simon.jeons@...il.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Mel Gorman <mgorman@...e.de>, Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan@...nel.org>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>
Subject: Re: [PATCH 2/3] mm, slub: count freed pages via rcu as this task's
 reclaimed_slab

Hi Christoph,
On 04/09/2013 10:32 PM, Christoph Lameter wrote:
> On Tue, 9 Apr 2013, Simon Jeons wrote:
>
>>> +	int pages = 1 << compound_order(page);
>> One question irrelevant this patch. Why slab cache can use compound
>> page(hugetlbfs pages/thp pages)? They are just used by app to optimize tlb
>> miss, is it?
> Slab caches can use any order pages because these pages are never on
> the LRU and are not part of the page cache. Large continuous physical
> memory means that objects can be arranged in a more efficient way in the
> page. This is particularly useful for larger objects where we might use a
> lot of memory because objects do not fit well into a 4k page.
>
> It also reduces the slab page management if higher order pages are used.
> In the case of slub the page size also determines the number of objects
> that can be allocated/freed without the need for some form of
> synchronization.

It seems that you misunderstand my question. I don't doubt slab/slub can 
use high order pages. However, what I focus on is why slab/slub can use 
compound page, PageCompound() just on behalf of hugetlbfs pages or thp 
pages which should used by apps, isn't it?

>

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