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

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Message-ID: <alpine.DEB.2.00.1108260950220.5818@router.home>
Date:	Fri, 26 Aug 2011 09:50:58 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Zhao Jin <cronozhj@...il.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, 26 Aug 2011, Zhao Jin wrote:

> 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.

Correct but still tthe del/add is a list_move operation. Convert that the
other case as well?

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