linux-kernel - [PATCH 2/3] fs/userfaultfd.c: reorder the if check to reduce some computation

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Date:   Fri, 13 Sep 2019 05:31:09 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     viro@...iv.linux.org.uk
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Wei Yang <richardw.yang@...ux.intel.com>
Subject: [PATCH 2/3] fs/userfaultfd.c: reorder the if check to reduce some computation

When there are several condition check in *if* clause, the check will
stop at the first false one.

Since the for loop iterates vma list, we are sure only the last vma
meets the condition "end <= vm_end". Reorder the check sequence to
reduce some computation.

Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
---
 fs/userfaultfd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 9ce09ac619a2..70c0e0ef01d7 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1402,7 +1402,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 		 * If this vma contains ending address, and huge pages
 		 * check alignment.
 		 */
-		if (is_vm_hugetlb_page(cur) && end <= cur->vm_end) {
+		if (end <= cur->vm_end && is_vm_hugetlb_page(cur)) {
 			unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
 
 			ret = -EINVAL;
-- 
2.17.1