[PATCH] mm/vmscan: restore allowed mask in alloc_demote_folio()

[Bing Jiao <bingjiao@google.com>]

In alloc_demote_folio(), mtc->nmask is set to NULL for the first
allocation. If that succeeds, it returns without restoring mtc->nmask
to allowed_mask. For subsequent allocations from the migrate_pages()
batch, mtc->nmask will be NULL. If the target node then becomes full,
the fallback allocation will use nmask = NULL, allocating from any
node allowed by the task cpuset, which for kswapd is all nodes.

To address this issue, restore the mtc->nmask to its original allowed
nodemask after the first allocation.

Signed-off-by: Bing Jiao <bingjiao@google.com>
---
 mm/vmscan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index cbffc0a27824..b42abd17aee7 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -985,11 +985,11 @@ static struct folio *alloc_demote_folio(struct folio *src,
 	mtc->nmask = NULL;
 	mtc->gfp_mask |= __GFP_THISNODE;
 	dst = alloc_migration_target(src, (unsigned long)mtc);
+	mtc->nmask = allowed_mask;
 	if (dst)
 		return dst;

 	mtc->gfp_mask &= ~__GFP_THISNODE;
-	mtc->nmask = allowed_mask;

 	return alloc_migration_target(src, (unsigned long)mtc);
 }
--
2.53.0.473.g4a7958ca14-goog