[PATCH] hugetlb: prioritize surplus allocation from current node

[Koichiro Den <koichiro.den@canonical.com>]

Previously, surplus allocations triggered by mmap were typically made
from the node where the process was running. On a page fault, the area
was reliably dequeued from the hugepage_freelists for that node.
However, since commit 003af997c8a9 ("hugetlb: force allocating surplus
hugepages on mempolicy allowed nodes"), dequeue_hugetlb_folio_vma() may
fall back to other nodes unnecessarily even if there is no MPOL_BIND
policy, causing folios to be dequeued from nodes other than the current
one.

Also, allocating from the node where the current process is running is
likely to result in a performance win, as mmap-ing processes often
touch the area not so long after allocation. This change minimizes
surprises for users relying on the previous behavior while maintaining
the benefit introduced by the commit.

So, prioritize the node the current process is running on when possible.

Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
---
 mm/hugetlb.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 5c8de0f5c760..0fa24e105202 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2463,7 +2463,13 @@ static int gather_surplus_pages(struct hstate *h, long delta)
 	long needed, allocated;
 	bool alloc_ok = true;
 	int node;
-	nodemask_t *mbind_nodemask = policy_mbind_nodemask(htlb_alloc_mask(h));
+	nodemask_t *mbind_nodemask, alloc_nodemask;
+
+	mbind_nodemask = policy_mbind_nodemask(htlb_alloc_mask(h));
+	if (mbind_nodemask)
+		nodes_and(alloc_nodemask, *mbind_nodemask, cpuset_current_mems_allowed);
+	else
+		alloc_nodemask = cpuset_current_mems_allowed;
 
 	lockdep_assert_held(&hugetlb_lock);
 	needed = (h->resv_huge_pages + delta) - h->free_huge_pages;
@@ -2479,8 +2485,16 @@ static int gather_surplus_pages(struct hstate *h, long delta)
 	spin_unlock_irq(&hugetlb_lock);
 	for (i = 0; i < needed; i++) {
 		folio = NULL;
-		for_each_node_mask(node, cpuset_current_mems_allowed) {
-			if (!mbind_nodemask || node_isset(node, *mbind_nodemask)) {
+
+		/* 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)
-- 
2.43.0