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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000013, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 31 Mar 2025, at 22:10, Vishal Moola (Oracle) wrote: > The compaction code doesn't take references on pages until we're certain > we should attempt to handle it. > > In the hugetlb case, isolate_or_dissolve_huge_page() may return -EBUSY > without taking a reference to the folio associated with our pfn. 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