[patch 115/173] mm/hugetlb: avoid unnecessary hugetlb_acct_memory() call

From: Miaohe Lin <linmiaohe@huawei.com>
Subject: mm/hugetlb: avoid unnecessary hugetlb_acct_memory() call

When reservation accounting remains unchanged, hugetlb_acct_memory() will
do nothing except holding and releasing hugetlb_lock.  We should avoid
this unnecessary hugetlb_lock lock/unlock cycle which is happening on
'most' hugetlb munmap operations by check delta against 0 at the beginning
of hugetlb_acct_memory.

Link: https://lkml.kernel.org/r/20210115092013.61012-1-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: David Hildenbrand <redacted>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: Mike Kravetz <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/hugetlb.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/mm/hugetlb.c~mm-hugetlb-avoid-unnecessary-hugetlb_acct_memory-call
+++ a/mm/hugetlb.c

@@ -3591,6 +3591,9 @@ static int hugetlb_acct_memory(struct hs
 {
 	int ret = -ENOMEM;
 
+	if (!delta)
+		return 0;
+
 	spin_lock(&hugetlb_lock);
 	/*
 	 * When cpuset is configured, it breaks the strict hugetlb page

_