[PATCH] mm/compaction: fix low_pfn advance on isolating hugetlb

[Wei Yang <richard.weiyang@gmail.com>]

Commit 56ae0bb349b4 ("mm: compaction: convert to use a folio in
isolate_migratepages_block()") converts api from page to folio. But the
low_pfn advance for hugetlb page seems wrong when low_pfn doesn't point
to head page.

Originally, if page is a hugetlb tail page, compound_nr() return 1,
which means low_pfn only advance one in next iteration. After the
change, low_pfn would advance more than the hugetlb range, since
folio_nr_pages() always return total number of the large page. This
results in skipping some range to isolate and then to migrate.

The worst case for alloc_contig is it does all the isolation and
migration, but finally find some range is still not isolated. And then
undo all the work and try a new range.

Advance low_pfn to the end of hugetlb.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Fixes: 56ae0bb349b4 ("mm: compaction: convert to use a folio in isolate_migratepages_block()")
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Oscar Salvador <osalvador@suse.de>
---
 mm/compaction.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index bf021b31c7ec..1e8f8eca318c 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -989,7 +989,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 				 * Hugepage was successfully isolated and placed
 				 * on the cc->migratepages list.
 				 */
-				low_pfn += folio_nr_pages(folio) - 1;
+				low_pfn += folio_nr_pages(folio) - folio_page_idx(folio, page) - 1;
 				goto isolate_success_no_list;
 			}
 
-- 
2.34.1