patches/old/mm-hugetlb-avoid-passing-a-null-nodemask-when-there-is-mbind-policy.patch

From: Oscar Salvador <osalvador@suse.de>
Subject: mm, hugetlb: avoid passing a null nodemask when there is mbind policy
Date: Tue, 15 Apr 2025 14:15:03 +0200

Before trying to allocate a page, gather_surplus_pages() sets up a
nodemask for the nodes we can allocate from, but instead of passing the
nodemask down the road to the page allocator, it iterates over the nodes
within that nodemask right there, meaning that the page allocator will
receive a preferred_nid and a null nodemask.

This is a problem when using a memory policy, because it might be that the
page allocator ends up using a node as a fallback which is not represented
in the policy.

Avoid that by passing the nodemask directly to the page allocator, so it
can filter out fallback nodes that are not part of the nodemask.

Link: https://lkml.kernel.org/r/20250415121503.376811-1-osalvador@suse.de
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: David Hildenbrand <david@redhat.com>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/hugetlb.c |   22 ++++++----------------
 1 file changed, 6 insertions(+), 16 deletions(-)

--- a/mm/hugetlb.c~mm-hugetlb-avoid-passing-a-null-nodemask-when-there-is-mbind-policy
+++ a/mm/hugetlb.c
@@ -2419,7 +2419,6 @@ static int gather_surplus_pages(struct h
 	long i;
 	long needed, allocated;
 	bool alloc_ok = true;
-	int node;
 	nodemask_t *mbind_nodemask, alloc_nodemask;
 
 	mbind_nodemask = policy_mbind_nodemask(htlb_alloc_mask(h));
@@ -2443,21 +2442,12 @@ retry:
 	for (i = 0; i < needed; i++) {
 		folio = NULL;
 
-		/* Prioritize current node */
-		if (node_isset(numa_mem_id(), alloc_nodemask))
-			folio = alloc_surplus_hugetlb_folio(h, htlb_alloc_mask(h),
-					numa_mem_id(), NULL);
-
-		if (!folio) {
-			for_each_node_mask(node, alloc_nodemask) {
-				if (node == numa_mem_id())
-					continue;
-				folio = alloc_surplus_hugetlb_folio(h, htlb_alloc_mask(h),
-						node, NULL);
-				if (folio)
-					break;
-			}
-		}
+		/*
+		 * It is okay to use NUMA_NO_NODE because we use numa_mem_id()
+		 * down the road to pick the current node if that is the case.
+		 */
+		folio = alloc_surplus_hugetlb_folio(h, htlb_alloc_mask(h),
+						    NUMA_NO_NODE, &alloc_nodemask);
 		if (!folio) {
 			alloc_ok = false;
 			break;
_