[016/143] mm/hugetlb: avoid calculating fault_mutex_hash in truncate_op case

Commit Message

Andrew Morton May 5, 2021, 1:33 a.m. UTC

From: Miaohe Lin <[e-mail]>
Subject: mm/hugetlb: avoid calculating fault_mutex_hash in truncate_op case

The fault_mutex hashing overhead can be avoided in truncate_op case
because page faults can not race with truncation in this routine.  So
calculate hash for fault_mutex only in !truncate_op case to save some cpu
cycles.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Miaohe Lin <[e-mail]>
Cc: Mike Kravetz <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 fs/hugetlbfs/inode.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Patch

--- a/fs/hugetlbfs/inode.c~mm-hugetlb-avoid-calculating-fault_mutex_hash-in-truncate_op-case
+++ a/fs/hugetlbfs/inode.c
@@ -482,10 +482,9 @@  static void remove_inode_hugepages(struc
 
 		for (i = 0; i < pagevec_count(&pvec); ++i) {
 			struct page *page = pvec.pages[i];
-			u32 hash;
+			u32 hash = 0;
 
 			index = page->index;
-			hash = hugetlb_fault_mutex_hash(mapping, index);
 			if (!truncate_op) {
 				/*
 				 * Only need to hold the fault mutex in the
@@ -493,6 +492,7 @@  static void remove_inode_hugepages(struc
 				 * page faults.  Races are not possible in the
 				 * case of truncation.
 				 */
+				hash = hugetlb_fault_mutex_hash(mapping, index);
 				mutex_lock(&hugetlb_fault_mutex_table[hash]);
 			}