Re: [PATCH -next v2 1/2] mm: compaction: convert to use a folio in isolate_migratepages_block()

[Kefeng Wang]

On 2023/6/21 14:20, Baolin Wang wrote:
> Hi
>
> On 6/19/2023 7:07 PM, Kefeng Wang wrote:
> > Directly use a folio instead of page_folio() when page successfully
> > isolated (hugepage and movable page) and after folio_get_nontail_page(),
> > which removes several calls to compound_head().
> >
> > Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> > ---
> > v2:
> > - update comments and use node_stat_mod_folio, per Matthew Wilcox
> > - add missed PageLRU conversion and rebase on next-20230619
> >
> >   mm/compaction.c | 84 ++++++++++++++++++++++++++-----------------------
> >   1 file changed, 44 insertions(+), 40 deletions(-)
> >
> > diff --git a/mm/compaction.c b/mm/compaction.c
> > index 6149a2d324be..0334eefe4bfa 100644
> > --- a/mm/compaction.c
> > +++ b/mm/compaction.c
> > @@ -795,6 +795,7 @@ isolate_migratepages_block(struct compact_control 
> > *cc, unsigned long low_pfn,
> >       struct lruvec *lruvec;
> >       unsigned long flags = 0;
> >       struct lruvec *locked = NULL;
> > +    struct folio *folio = NULL;
> >       struct page *page = NULL, *valid_page = NULL;
> >       struct address_space *mapping;
> >       unsigned long start_pfn = low_pfn;
> > @@ -891,7 +892,7 @@ isolate_migratepages_block(struct compact_control 
> > *cc, unsigned long low_pfn,
> >           if (!valid_page && pageblock_aligned(low_pfn)) {
> >               if (!isolation_suitable(cc, page)) {
> >                   low_pfn = end_pfn;
> > -                page = NULL;
> > +                folio = NULL;
> >                   goto isolate_abort;
> >               }
> >               valid_page = page;
> > @@ -923,7 +924,8 @@ isolate_migratepages_block(struct compact_control 
> > *cc, unsigned long low_pfn,
> >                    * Hugepage was successfully isolated and placed
> >                    * on the cc->migratepages list.
> >                    */
> > -                low_pfn += compound_nr(page) - 1;
> > +                folio = page_folio(page);
> > +                low_pfn += folio_nr_pages(folio) - 1;
> >                   goto isolate_success_no_list;
> >               }
> > @@ -991,8 +993,10 @@ isolate_migratepages_block(struct compact_control 
> > *cc, unsigned long low_pfn,
> >                       locked = NULL;
> >                   }
> > -                if (isolate_movable_page(page, mode))
> > +                if (isolate_movable_page(page, mode)) {
> > +                    folio = page_folio(page);
> >                       goto isolate_success;
> > +                }
> >               }
> >               goto isolate_fail;
> > @@ -1003,7 +1007,8 @@ isolate_migratepages_block(struct 
> > compact_control *cc, unsigned long low_pfn,
> >            * sure the page is not being freed elsewhere -- the
> >            * page release code relies on it.
> >            */
> > -        if (unlikely(!get_page_unless_zero(page)))
> > +        folio = folio_get_nontail_page(page);
>
> I'm just curious, how can you make sure the 'page' is not a tail page? 
> Since the validation is lockless.

folio_get_nontail_page is added by commit "3c1ea2c729ef (mm: add
folio_get_nontail_page())", see more comments [1]

[1] https://lore.kernel.org/lkml/Y86sRiKAAOz2myNe@xxxxxxxxxxxxxxxxxxxx/

>