mm: avoid possible multiple call to swap_node()

Commit Message

Miaohe Lin Sept. 17, 2020, 11:44 a.m. UTC

Cache the swap_node() in a local variable to avoid possible multiple call
to swap_node(), though compiler may do this for us.

Signed-off-by: Miaohe Lin <[e-mail]>
---
 mm/swapfile.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Comments

Matthew Wilcox Sept. 17, 2020, 11:48 a.m. UTC | #1

On Thu, Sep 17, 2020 at 07:44:49AM -0400, Miaohe Lin wrote:
> Cache the swap_node() in a local variable to avoid possible multiple call
> to swap_node(), though compiler may do this for us.

Why don't you find out?  Compare the assembly before and after, see what
the compiler did.

Patch

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 20012c0c0252..cd66b50f0490 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2454,7 +2454,7 @@  static void setup_swap_info(struct swap_info_struct *p, int prio,
 			    unsigned char *swap_map,
 			    struct swap_cluster_info *cluster_info)
 {
-	int i;
+	int i, node;
 
 	if (prio >= 0)
 		p->prio = prio;
@@ -2465,11 +2465,12 @@  static void setup_swap_info(struct swap_info_struct *p, int prio,
 	 * low-to-high, while swap ordering is high-to-low
 	 */
 	p->list.prio = -p->prio;
+	node = swap_node(p);
 	for_each_node(i) {
 		if (p->prio >= 0)
 			p->avail_lists[i].prio = -p->prio;
 		else {
-			if (swap_node(p) == i)
+			if (node == i)
 				p->avail_lists[i].prio = 1;
 			else
 				p->avail_lists[i].prio = -p->prio;