[patch 1/9] mm: migrate: use thp_order instead of HPAGE_PMD_ORDER for new page allocation.

[Andrew Morton <akpm@linux-foundation.org>]

From: Zi Yan <ziy@nvidia.com>
Subject: mm: migrate: use thp_order instead of HPAGE_PMD_ORDER for new page allocation.

Fix a VM_BUG_ON_FOLIO(folio_nr_pages(old) != nr_pages) crash.

With folios support, it is possible to have other than HPAGE_PMD_ORDER
THPs, in the form of folios, in the system.  Use thp_order() to correctly
determine the source page order during migration.

Link: https://lkml.kernel.org/r/20220404165325.1883267-1-zi.yan@sent.com
Link: https://lore.kernel.org/linux-mm/20220404132908.GA785673@u2004/
Fixes: d68eccad3706 ("mm/filemap: Allow large folios to be added to the page cache")
Reported-by: Naoya Horiguchi <naoya.horiguchi@linux.dev>
Signed-off-by: Zi Yan <ziy@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/mempolicy.c |    2 +-
 mm/migrate.c   |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

--- a/mm/mempolicy.c~mm-migrate-use-thp_order-instead-of-hpage_pmd_order-for-new-page-allocation
+++ a/mm/mempolicy.c
@@ -1209,7 +1209,7 @@ static struct page *new_page(struct page
 		struct page *thp;
 
 		thp = alloc_hugepage_vma(GFP_TRANSHUGE, vma, address,
-					 HPAGE_PMD_ORDER);
+					 thp_order(page));
 		if (!thp)
 			return NULL;
 		prep_transhuge_page(thp);
--- a/mm/migrate.c~mm-migrate-use-thp_order-instead-of-hpage_pmd_order-for-new-page-allocation
+++ a/mm/migrate.c
@@ -1547,7 +1547,7 @@ struct page *alloc_migration_target(stru
 		 */
 		gfp_mask &= ~__GFP_RECLAIM;
 		gfp_mask |= GFP_TRANSHUGE;
-		order = HPAGE_PMD_ORDER;
+		order = thp_order(page);
 	}
 	zidx = zone_idx(page_zone(page));
 	if (is_highmem_idx(zidx) || zidx == ZONE_MOVABLE)
_