On Tue, Jun 25, 2019 at 12:28:56PM +0200, David Hildenbrand wrote:
> > +static __always_inline void __ClearPageVmemmap(struct page *page)
> > +{
>
> Should we VM_BUG_ON in case !PG_reserved || pg->mapping != VMEMMAP_PAGE ?
We can do that, just for extra protection.
>
> > + __ClearPageReserved(page);
> > + page->mapping = NULL;
> > +}
> > +
> > +static __always_inline void __SetPageVmemmap(struct page *page)
> > +{
>
> Should we VM_BUG_ON in case PG_reserved || pg->mapping != NULL ?
ditto.
>
> > + __SetPageReserved(page);
> > + page->mapping = (void *)VMEMMAP_PAGE;
> > +}
> > +
> > +static __always_inline struct page *vmemmap_get_head(struct page *page)
> > +{
> > + return (struct page *)page->freelist;
>
> freelist is a "slab, slob and slub" concept (reading
> include/linux/mm_types.h). page->mapping is a "Page cache and anonymous
> pages" concept. Hmmm...
Yeah.
In an early stage, I thought about constructing vmemmap pages the same way
we construct compound pages, so we can leverage the APIs that we already have.
For some reason I did not go further with that, but I will investigate in that
direction.
> I wonder if using a page type would be appropriate here instead. Then,
> define a new sub-structure within "struct page" that describes what you
> actually want (instead of reusing ->private and ->mapping). Just an
> idea, we have to find out if that is possible.
>
> vmemmap_get_head() smells like __GFP_COMP, but of course, these vmemmap
> pages never saw the buddy. But sounds like you want a similar concept.
Thanks for the feedback.
I will take a look at it.
--
Oscar Salvador
SUSE L3
