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

[Kefeng Wang]

On 2023/6/13 9:53, Kefeng Wang wrote:
> On 2023/6/12 22:41, Matthew Wilcox wrote:
> > On Mon, Jun 12, 2023 at 10:34:13PM +0800, Kefeng Wang wrote:
> > > @@ -959,7 +960,8 @@ 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;
> >
> > Why is this safe?  That is, how do we know that the folio can't be
> > dissolved under us at this point, then reallocated and hit the
> > VM_BUG_ON_PGFLAGS(PageTail(page), page) in folio_flags() when we
> > test folio_test_large()?
>
> This is successfully isolated path, after isolate_hugetlb(),  the folio
> reference is incremented, so I think the folio can't be dissolved here,
> correct me if I am wrong.

Hi Matthew，is it enough for the above conversion from page to folio with 
reference?