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

[Zhao Jin <cronozhj@gmail.com>]

On Fri, 2011-08-26 at 09:50 -0500, Christoph Lameter wrote:
> 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?
> 
Yes. The patch avoids list_del/list_add only if it is the case that a
partial slab was used for refilling and remains partial (that is:
partial => partial). If it is not the case( so it must be either partial
=> full, free => full or free => partial) the patched code behaves the
same as current (list_del/list_add).

Regards,
zhj