Re: [Xen-devel] [PATCH v5 1/4] xen: move steal_page and donate_page to common code

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 10 Sep 2013, Tim Deegan wrote:
> At 18:20 +0100 on 10 Sep (1378837226), Stefano Stabellini wrote:
> > On Tue, 10 Sep 2013, Jan Beulich wrote:
> > > >>> On 09.09.13 at 18:06, Stefano Stabellini 
> > > >>> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> > > > --- a/xen/common/memory.c
> > > > +++ b/xen/common/memory.c
> > > > @@ -230,6 +230,91 @@ int guest_remove_page(struct domain *d, unsigned 
> > > > long gmfn)
> > > >      return 1;
> > > >  }
> > > >  
> > > > +int donate_page(
> > > > +    struct domain *d, struct page_info *page, unsigned int memflags)
> > > > +{
> > > > +    spin_lock(&d->page_alloc_lock);
> > > > +
> > > > +    if ( is_xen_heap_page(page) || (page_get_owner(page) != NULL) )
> > > > +        goto fail;
> > > > +
> > > > +    if ( d->is_dying )
> > > > +        goto fail;
> > > > +
> > > > +    if ( page->count_info & ~(PGC_allocated | 1) )
> > > 
> > > While the literal 1 was acceptable in arch specific code, I'm not sure
> > > it really is in generic code. Nothing enforces that an arch has the
> > > count starting at bit 0. Even if it reads a little odd, using
> > > (-PGC_count_mask & PGC_count_mask) would probably be an
> > > acceptable replacement here and further down.
> > 
> > (-PGC_count_mask & PGC_count_mask) is always 0.
> 
> 'x & -x' always gives you the lowest set bit in x, though as Jan points
> out it's a bit opaque.  Maybe it needs a friendly macro name?

No that's fine. I read it as ~PGC_count_mask.
It proves that I need new glasses or a larger font size :P

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel