[PATCH v2 4/4] mm/hugetl.c: warn out if expected count of huge pages adjustment is not achieved

[Baoquan He <bhe@redhat.com>]

A customer complained that no message is logged when the number of
persistent huge pages is not changed to the exact value written to
the sysfs or proc nr_hugepages file.

In the current code, a best effort is made to satisfy requests made
via the nr_hugepages file.  However, requests may be only partially
satisfied.

Log a message if the code was unsuccessful in fully satisfying a
request. This includes both increasing and decreasing the number
of persistent huge pages.

Signed-off-by: Baoquan He <bhe@redhat.com>
---
 mm/hugetlb.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index c14837854392..b5aa32a13569 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2661,7 +2661,7 @@ static int adjust_pool_surplus(struct hstate *h, nodemask_t *nodes_allowed,
 static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
 			      nodemask_t *nodes_allowed)
 {
-	unsigned long min_count, ret;
+	unsigned long min_count, ret, old_max, new_max;
 	NODEMASK_ALLOC(nodemask_t, node_alloc_noretry, GFP_KERNEL);
 
 	/*
@@ -2723,6 +2723,7 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
 	 * pool might be one hugepage larger than it needs to be, but
 	 * within all the constraints specified by the sysctls.
 	 */
+	old_max = persistent_huge_pages(h);
 	while (h->surplus_huge_pages && count > persistent_huge_pages(h)) {
 		if (!adjust_pool_surplus(h, nodes_allowed, -1))
 			break;
@@ -2779,8 +2780,20 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
 	}
 out:
 	h->max_huge_pages = persistent_huge_pages(h);
+	new_max = h->max_huge_pages;
 	spin_unlock(&hugetlb_lock);
 
+	if (count != new_max) {
+		char buf[32];
+
+		string_get_size(huge_page_size(h), 1, STRING_UNITS_2, buf, 32);
+		pr_warn("HugeTLB: %s %lu of page size %s failed. Only %s %lu hugepages.\n",
+			count > old_max ? "increasing" : "decreasing",
+			abs(count - old_max), buf,
+			count > old_max ? "increased" : "decreased",
+			abs(old_max - new_max));
+	}
+
 	NODEMASK_FREE(node_alloc_noretry);
 
 	return 0;
-- 
2.17.2