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/20210308112809.26107-6-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index c262566..d81f52b 100644 (file)
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -482,10 +482,9 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
 
                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(struct inode *inode, loff_t lstart,
                                 * 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]);
                        }