linux-kernel - Re: [PATCH 09/16] mm/slab: put the freelist at the end of slab page

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Date:	Fri, 15 Jan 2016 01:21:54 +0900
From:	Joonsoo Kim <js1304@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Linux Memory Management List <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 09/16] mm/slab: put the freelist at the end of slab page

2016-01-15 0:26 GMT+09:00 Christoph Lameter <cl@...ux.com>:
> On Thu, 14 Jan 2016, Joonsoo Kim wrote:
>
>> Currently, the freelist is at the front of slab page. This requires
>> extra space to meet object alignment requirement. If we put the freelist
>> at the end of slab page, object could start at page boundary and will
>> be at correct alignment. This is possible because freelist has
>> no alignment constraint itself.
>>
>> This gives us two benefits. It removes extra memory space
>> for the freelist alignment and remove complex calculation
>> at cache initialization step. I can't think notable drawback here.
>
>
> The third one is that the padding space at the end of the slab could
> actually be used for the freelist if it fits.

Yes.

> The drawback may be that the location of the freelist at the beginning of
> the page is more cache effective because the cache prefetcher may be able
> to get the following cachelines and effectively hit the first object.
> However, this is rather dubious speculation.

I think so, too. :)
If then, could you give me an ack?

Thanks.