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SubjectRe: [PATCH 13/15] sched: Set preferred NUMA node based on number of private faults
On Sat, Jul 06, 2013 at 12:41:07PM +0200, Peter Zijlstra wrote:
> On Sat, Jul 06, 2013 at 12:09:00AM +0100, Mel Gorman wrote:
> > +++ b/include/linux/mm.h
> > @@ -582,11 +582,11 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
> > * sets it, so none of the operations on it need to be atomic.
> > */
> >
> > -/* Page flags: | [SECTION] | [NODE] | ZONE | [LAST_NID] | ... | FLAGS | */
> > +/* Page flags: | [SECTION] | [NODE] | ZONE | [LAST_NIDPID] | ... | FLAGS | */
> > #define SECTIONS_PGOFF ((sizeof(unsigned long)*8) - SECTIONS_WIDTH)
> > #define NODES_PGOFF (SECTIONS_PGOFF - NODES_WIDTH)
> > #define ZONES_PGOFF (NODES_PGOFF - ZONES_WIDTH)
> > -#define LAST_NID_PGOFF (ZONES_PGOFF - LAST_NID_WIDTH)
> > +#define LAST_NIDPID_PGOFF (ZONES_PGOFF - LAST_NIDPID_WIDTH)
>
> I saw the same with Ingo's patch doing the similar thing. But why do we fuse
> these two into a single field? Would it not make more sense to have them be
> separate fields?
>
> Yes I get we update and read them together, and we could still do that with
> appropriate helper function, but they are two independent values stored in the
> page flags.
>

There were two reasons. First, it is because we update and read them
together. Second, it's all or nothing if this field is included in the
page->flags or not. I know this could also be done with helpers and
other tricks but I did not think it would be any easier to understand.

--
Mel Gorman
SUSE Labs


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