Re: [PATCH mm-unstable v5 01/10] mm: add folio dtor and order setter functions

Mike Kravetz
2022-12-07T03:42:51Z

On 12/07/22 11:34, Muchun Song wrote:
>
>
> > On Nov 30, 2022, at 06:50, Sidhartha Kumar <sidhartha.kumar@oracle.com> wrote:
> >
> > Add folio equivalents for set_compound_order() and set_compound_page_dtor().
> >
> > Also remove extra new-lines introduced by mm/hugetlb: convert
> > move_hugetlb_state() to folios and mm/hugetlb_cgroup: convert
> > hugetlb_cgroup_uncharge_page() to folios.
> >
> > Suggested-by: Mike Kravetz <mike.kravetz@oracle.com>
> > Suggested-by: Muchun Song <songmuchun@bytedance.com>
> > Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
> > ---
> > include/linux/mm.h | 16 ++++++++++++++++
> > mm/hugetlb.c | 4 +---
> > 2 files changed, 17 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index a48c5ad16a5e..2bdef8a5298a 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -972,6 +972,13 @@ static inline void set_compound_page_dtor(struct page *page,
> > page[1].compound_dtor = compound_dtor;
> > }
> >
> > +static inline void folio_set_compound_dtor(struct folio *folio,
> > + enum compound_dtor_id compound_dtor)
> > +{
> > + VM_BUG_ON_FOLIO(compound_dtor >= NR_COMPOUND_DTORS, folio);
> > + folio->_folio_dtor = compound_dtor;
> > +}
> > +
> > void destroy_large_folio(struct folio *folio);
> >
> > static inline int head_compound_pincount(struct page *head)
> > @@ -987,6 +994,15 @@ static inline void set_compound_order(struct page *page, unsigned int order)
> > #endif
> > }
> >
> > +static inline void folio_set_compound_order(struct folio *folio,
> > + unsigned int order)
> > +{
> > + folio->_folio_order = order;
> > +#ifdef CONFIG_64BIT
> > + folio->_folio_nr_pages = order ? 1U << order : 0;
>
> It seems that you think the user could pass 0 to order. However,
> ->_folio_nr_pages and ->_folio_order fields are invalid for order-0 pages.
> You should not touch it. So this should be:
>
> static inline void folio_set_compound_order(struct folio *folio,
> unsigned int order)
> {
> if (!folio_test_large(folio))
> return;
>
> folio->_folio_order = order;
> #ifdef CONFIG_64BIT
> folio->_folio_nr_pages = 1U << order;
> #endif
> }

I believe this was changed to accommodate the code in
__destroy_compound_gigantic_page(). It is used in a subsequent patch.
Here is the v6.0 version of the routine.

static void __destroy_compound_gigantic_page(struct page *page,
unsigned int order, bool demote)
{
int i;
int nr_pages = 1 << order;
struct page *p = page + 1;

atomic_set(compound_mapcount_ptr(page), 0);
atomic_set(compound_pincount_ptr(page), 0);

for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
p->mapping = NULL;
clear_compound_head(p);
if (!demote)
set_page_refcounted(p);
}

set_compound_order(page, 0);
#ifdef CONFIG_64BIT
page[1].compound_nr = 0;
#endif
__ClearPageHead(page);
}

Might have been better to change this set_compound_order call to
folio_set_compound_order in this patch.
--
Mike Kravetz