linux-kernel - Re: [PATCH] slab: avoid unnecessary touching of a partial slab

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Message-ID: <1314370016.8991.38.camel@vm>
Date:	Fri, 26 Aug 2011 22:46:56 +0800
From:	Zhao Jin <cronozhj@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	penberg@...nel.org, mpm@...enic.com, trivial@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] slab: avoid unnecessary touching of a partial slab

On Fri, 2011-08-26 at 09:08 -0500, Christoph Lameter wrote:
> On Fri, 26 Aug 2011, Zhao Jin wrote:
> 
> > In cache_alloc_refill(), after refilling from a partial slab, if the
> > slab remains partial, it would be deleted from and then added again to
> > the partial list. As the slab is the first element in the list before
> > deletion, such behavior has no effect. This patch avoids touching the
> > slab in this case.
> 
> The list_del/list_add action is a list_move.

But in cache_alloc_refill(), it is the first slab (that is: its list
field is pointed by the l3->slabs_partial.next) that is picked from the
partial list for refilling. Assume it remains partial after that. Since
list_add inserts a new element after the head (l3->slabs_partial), the
position of the slab in the partial list won't change after
list_del/list_add: it will be still the first element. Therefore,
list_del/list_add has done nothing actually in this case.

Regards,
zhj

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