On Thu, Apr 04, 2024 at 01:05:57AM +0100, Matthew Wilcox wrote:
> On Tue, Apr 02, 2024 at 09:32:47PM -0400, peterx@xxxxxxxxxx wrote:
> > +++ b/include/linux/page-flags.h
> > @@ -1095,7 +1095,13 @@ PAGEFLAG(Isolated, isolated, PF_ANY);
> > static __always_inline int PageAnonExclusive(const struct page *page)
> > {
> > VM_BUG_ON_PGFLAGS(!PageAnon(page), page);
> > - VM_BUG_ON_PGFLAGS(PageHuge(page) && !PageHead(page), page);
> > + /*
> > + * Allow the anon-exclusive check to work on hugetlb tail pages.
> > + * Here hugetlb pages will always guarantee the anon-exclusiveness
> > + * of the head page represents the tail pages.
> > + */
> > + if (PageHuge(page) && !PageHead(page))
> > + page = compound_head(page);
>
> I think this should be written as:
>
> /*
> * HugeTLB stores this information on the head page; THP keeps
> * it per page
> */
This comment does look clean and cleaner indeed. And yes, mention THP can
be helpful too.
> if (PageHuge(page))
> page = compound_head(page);
I would think PageHead() check would help us to avoid compound_head() on
heads, which should still be the majority cases iiuc (assuming page->flags
is already around in the cache anyway). I've no strong opinion though, as
I can hardly tell a difference in reality.
>
> > return test_bit(PG_anon_exclusive, &PF_ANY(page, 1)->flags);
> > }
>
Thanks,
--
Peter Xu
