[PATCH 02/15] mm/hugetlb: compare against persistent count when freeing lowmem folios

[David Hildenbrand (Arm)]

try_to_free_low() gets a target number of persistent folios, but
compares it with "nr_huge_pages", which includes surplus folios. As a
result, it can free lowmem folios below that target.

For example, with two persistent folios and one surplus folio, a target
of two can still end up freeing one persistent folio.

Compare against persistent_huge_pages() instead. Convert the macro to a
helper function and place it before try_to_free_low().

Fixes: 7893d1d505d5 ("hugetlb: Try to grow hugetlb pool for MAP_PRIVATE mappings")
Cc: stable@xxxxxxxxxx
Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
---
 mm/hugetlb.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index da5d04edf7c1..3a94ea1c9457 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1335,6 +1335,11 @@ static unsigned long available_huge_pages(struct hstate *h)
 	return h->free_huge_pages - h->resv_huge_pages;
 }
 
+static unsigned long persistent_huge_pages(struct hstate *h)
+{
+	return h->nr_huge_pages - h->surplus_huge_pages;
+}
+
 static struct folio *dequeue_hugetlb_folio(struct hstate *h, gfp_t gfp_mask,
 					   struct mempolicy_interpreted *mpoli)
 {
@@ -3719,7 +3724,7 @@ static void try_to_free_low(struct hstate *h, unsigned long count,
 		struct folio *folio, *next;
 		struct list_head *freel = &h->hugepage_freelists[i];
 		list_for_each_entry_safe(folio, next, freel, lru) {
-			if (count >= h->nr_huge_pages)
+			if (count >= persistent_huge_pages(h))
 				goto out;
 			if (folio_test_highmem(folio))
 				continue;
@@ -3773,7 +3778,6 @@ static int adjust_pool_surplus(struct hstate *h, nodemask_t *nodes_allowed,
 	return 1;
 }
 
-#define persistent_huge_pages(h) (h->nr_huge_pages - h->surplus_huge_pages)
 static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
 			      nodemask_t *nodes_allowed)
 {

-- 
2.43.0