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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
