Re: [patch 2] mm: speculative get_page

[Nick Piggin <nickpiggin@yahoo.com.au>]

Nick Piggin wrote:
> William Lee Irwin III wrote:
>
> > On Mon, Jun 27, 2005 at 04:32:38PM +1000, Nick Piggin wrote:
> >
> > > +static inline struct page *page_cache_get_speculative(struct page 
> > > **pagep)
> > > +{
> > > +    struct page *page;
> > > +
> > > +    preempt_disable();
> > > +    page = *pagep;
> > > +    if (!page)
> > > +        goto out_failed;
> > > +
> > > +    if (unlikely(get_page_testone(page))) {
> > > +        /* Picked up a freed page */
> > > +        __put_page(page);
> > > +        goto out_failed;
> > > +    }
> >
> >
> >
> > So you pick up 0->1 refcount transitions.
>
> Yep ie. a page that's freed or being freed.

Oh, one thing it does need is a check for PageFree(), so it also
picks up 1->2 and other transitions without freeing the free page
if the put()s are done out of order. Maybe that's what you were
alluding to.

I'll add that.

--
SUSE Labs, Novell Inc.

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