hugetlb: force allocating surplus hugepages on mempolicy allowed nodes

JIRA: https://issues.redhat.com/browse/RHEL-38605
Tested: by reporter

commit 003af99
Author: Aristeu Rozanski <aris@redhat.com>
Date:   Fri Jun 21 15:00:50 2024 -0400

    hugetlb: force allocating surplus hugepages on mempolicy allowed nodes

    When trying to allocate a hugepage with no reserved ones free, it may be
    allowed in case a number of overcommit hugepages was configured (using
    /proc/sys/vm/nr_overcommit_hugepages) and that number wasn't reached.
    This allows for a behavior of having extra hugepages allocated
    dynamically, if there're resources for it.  Some sysadmins even prefer not
    reserving any hugepages and setting a big number of overcommit hugepages.

    But while attempting to allocate overcommit hugepages in a multi node
    system (either NUMA or mempolicy/cpuset) said allocations might randomly
    fail even when there're resources available for the allocation.

    This happens due to allowed_mems_nr() only accounting for the number of
    free hugepages in the nodes the current process belongs to and the surplus
    hugepage allocation is done so it can be allocated in any node.  In case
    one or more of the requested surplus hugepages are allocated in a
    different node, the whole allocation will fail due allowed_mems_nr()
    returning a lower value.

    So allocate surplus hugepages in one of the nodes the current process
    belongs to.

    Easy way to reproduce this issue is to use a 2+ NUMA nodes system:

            # echo 0 >/proc/sys/vm/nr_hugepages
            # echo 1 >/proc/sys/vm/nr_overcommit_hugepages
            # numactl -m0 ./tools/testing/selftests/mm/map_hugetlb 2

    Repeating the execution of map_hugetlb test application will eventually
    fail when the hugepage ends up allocated in a different node.

    [aris@ruivo.org: v2]
      Link: https://lkml.kernel.org/r/20240701212343.GG844599@cathedrallabs.org
    Link: https://lkml.kernel.org/r/20240621190050.mhxwb65zn37doegp@redhat.com
    Signed-off-by: Aristeu Rozanski <aris@redhat.com>
    Cc: Muchun Song <muchun.song@linux.dev>
    Cc: Aristeu Rozanski <aris@ruivo.org>
    Cc: David Hildenbrand <david@redhat.com>
    Cc: Vishal Moola <vishal.moola@gmail.com>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Aristeu Rozanski <arozansk@redhat.com>

Author: aristeu

mm/hugetlb.c

@@ -2580,6 +2580,23 @@ struct folio *alloc_hugetlb_folio_vma(struct hstate *h, struct vm_area_struct *v
 	return folio;
 }
 
+static nodemask_t *policy_mbind_nodemask(gfp_t gfp)
+{
+#ifdef CONFIG_NUMA
+	struct mempolicy *mpol = get_task_policy(current);
+
+	/*
+	 * Only enforce MPOL_BIND policy which overlaps with cpuset policy
+	 * (from policy_nodemask) specifically for hugetlb case
+	 */
+	if (mpol->mode == MPOL_BIND &&
+		(apply_policy_zone(mpol, gfp_zone(gfp)) &&
+		 cpuset_nodemask_valid_mems_allowed(&mpol->nodes)))
+		return &mpol->nodes;
+#endif
+	return NULL;
+}
+
 /*
  * Increase the hugetlb pool such that it can accommodate a reservation
  * of size 'delta'.
@@ -2594,6 +2611,8 @@ static int gather_surplus_pages(struct hstate *h, long delta)
 	long i;
 	long needed, allocated;
 	bool alloc_ok = true;
+	int node;
+	nodemask_t *mbind_nodemask = policy_mbind_nodemask(htlb_alloc_mask(h));
 
 	lockdep_assert_held(&hugetlb_lock);
 	needed = (h->resv_huge_pages + delta) - h->free_huge_pages;
@@ -2608,8 +2627,15 @@ static int gather_surplus_pages(struct hstate *h, long delta)
 retry:
 	spin_unlock_irq(&hugetlb_lock);
 	for (i = 0; i < needed; i++) {
-		folio = alloc_surplus_hugetlb_folio(h, htlb_alloc_mask(h),
-				NUMA_NO_NODE, NULL);
+		folio = NULL;
+		for_each_node_mask(node, cpuset_current_mems_allowed) {
+			if (!mbind_nodemask || node_isset(node, *mbind_nodemask)) {
+				folio = alloc_surplus_hugetlb_folio(h, htlb_alloc_mask(h),
+						node, NULL);
+				if (folio)
+					break;
+			}
+		}
 		if (!folio) {
 			alloc_ok = false;
 			break;
@@ -4589,23 +4615,6 @@ static int __init default_hugepagesz_setup(char *s)
 }
 __setup("default_hugepagesz=", default_hugepagesz_setup);
 
-static nodemask_t *policy_mbind_nodemask(gfp_t gfp)
-{
-#ifdef CONFIG_NUMA
-	struct mempolicy *mpol = get_task_policy(current);
-
-	/*
-	 * Only enforce MPOL_BIND policy which overlaps with cpuset policy
-	 * (from policy_nodemask) specifically for hugetlb case
-	 */
-	if (mpol->mode == MPOL_BIND &&
-		(apply_policy_zone(mpol, gfp_zone(gfp)) &&
-		 cpuset_nodemask_valid_mems_allowed(&mpol->nodes)))
-		return &mpol->nodes;
-#endif
-	return NULL;
-}
-
 static unsigned int allowed_mems_nr(struct hstate *h)
 {
 	int node;