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If our > folio's refcount drops to 0, compound_nr() becomes unpredictable, making > low_pfn and nr_scanned unreliable. > The user-visible effect is minimal - this should rarely happen (if ever). > > Fix this by storing the folio statistics earlier on the stack (just like > the THP and Buddy cases). > > Also revert commit 66fe1cf7f581 ("mm: compaction: use helper compound_nr > in isolate_migratepages_block") > to make backporting easier. > > Fixes: 369fa227c219 ("mm: make alloc_contig_range handle free hugetlb pag= es") > Cc: Miaohe Lin > Cc: Oscar Salvador > Signed-off-by: Vishal Moola (Oracle) > --- > mm/compaction.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > @@ -1011,8 +1011,8 @@ isolate_migratepages_block(struct compact_control *= cc, unsigned long low_pfn, > /* Do not report -EBUSY down the chain */ > if (ret =3D=3D -EBUSY) > ret =3D 0; > - low_pfn +=3D compound_nr(page) - 1; > - nr_scanned +=3D compound_nr(page) - 1; > + low_pfn +=3D (1UL << order) - 1; > + nr_scanned +=3D (1UL << order) - 1; > goto isolate_fail; > } > Right after this, there is =E2=80=9Clow_pfn +=3D folio_nr_pages(folio) - 1= =E2=80=9D for isolated hugetlb. I wonder if that can use order as well. Maybe not, since the order is obtained without taking a reference, but folio_nr_pages(= ) is called with a reference. They might be different. Anyway, Reviewed-by: Zi Yan Best Regards, Yan, Zi