On Fri, Feb 09, 2018 at 10:43:19AM -0800, Dave Hansen wrote:
> On 02/09/2018 07:28 AM, Matthew Wilcox wrote:
> > union {
> > + /*
> > + * If the page is neither PageSlab nor PageAnon, the value
> > + * stored here may help distinguish it from page cache pages.
> > + * See page-flags.h for a list of page types which are
> > + * currently stored here.
> > + */
> > + unsigned int page_type;
> > +
> > _slub_counter_t counters;
> > unsigned int active; /* SLAB */
> > struct { /* SLUB */
>
> Are there any straightforward rules that we can enforce here? For
> instance, if you are using "page_type", you can never have PG_lru set.
>
> Not that we have done this at all for 'struct page' historically, it
> would be really convenient to have a clear definition for when
> "page_type" is valid vs. "_mapcount".
I agree, it'd be nice. I think the only invariant we can claim to be
true is that if PageSlab is set then page_type is not valid. There are
probably any number of bits in the page->flags that aren't currently in
use by any of the consumers who actually set page_type, but I don't feel
like there's a straightforward rule that we can enforce. Maybe they'll
want to start using them in the future for their own purposes.
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
