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

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Date:	Thu, 11 Apr 2013 11:46:24 +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 04/10/2013 09:54 PM, Christoph Lameter wrote:
> On Wed, 10 Apr 2013, Simon Jeons wrote:
>
>> 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?
> I am not entirely clear on what you are asking for. The following gives a
> couple of answers to what I guess the question was.
>
> THP pages and user pages are on the lru and are managed differently.
> The slab allocators cannot work with those pages.
>
> Slab allocators *can* allocate higher order pages therefore they could
> allocate a page of the same order as huge pages and manage it that way.
>
> However there is no way that these pages could be handled like THP pages
> since they cannot be broken up (unless we add the capability to move slab
> objects which I wanted to do for a long time).
>
>
> You can boot a Linux system that uses huge pages for slab allocation
> by specifying the following parameter on the kernel command line.
>
> 	slub_min_order=9
>
> The slub allocator will start using huge pages for all its storage
> needs. You need a large number of huge pages to do this. Lots of memory
> is going to be lost due to fragmentation but its going to be fast since
> the slowpaths are rarely used. OOMs due to reclaim failure become much
> more likely ;-).
>

It seems that I need to simple my question.
All pages which order >=1 are compound pages?


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