Re: SLUB: Define functions for cpu slab handling instead of using PageActive

[Christoph Lameter <clameter@sgi.com>]

On Mon, 14 May 2007, Andrew Morton wrote:

> On Mon, 14 May 2007 20:00:07 -0700 (PDT) Christoph Lameter <clameter@sgi.com> wrote:
> 
> > Use inline functions to access the per cpu bit. Intoduce the notion of 
> > "freezing" a slab to make things more understandable.
> > 
> > ...
> >
> > +static inline void ClearSlabFrozen(struct page *page)
> > +{
> > +	__ClearPageActive(page);
> > +}
> 
> Non-atomic.
> 
> > -	ClearPageActive(page);
> 
> Atomic.
> 
> A substitution like this can lead to quite revoltingly subtle bugs and needs
> lots of justfication.
> 
> I'll switch this back to the atomic version.  If you're really sure about
> this micro-optimisation then let's do it as a standalone patch.  One which
> adds a comment explaining why it is safe, and under which circumstances it
> will become unsafe, etc.

There is no need for atomics here since the flag is only modified with the 
slab lock taken but there is no __SetPageActive.

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