[PATCH 2/3] mm/swapfile.c: use swap_info[] to find the swap device

[Baoquan He <bhe@redhat.com>]

Now, swap_active_head is only used to find a present swap device when
trying to swapoff it. In fact, swap_info[] is a short array which is
32 at maximum, and usually the unused one can be reused, so the
searching for target mostly only iterates the foremost several used
slots. And swapoff is a rarely used operation, efficiency is not so
important. Then it's unnecessary to get a plist to make it.

Here go by iterating swap_info[] to find the swap device instead of
iterating swap_active_head.

Signed-off-by: Baoquan He <bhe@redhat.com>
---
 mm/swapfile.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 5d71c748a2fe..18b52cc20749 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2641,6 +2641,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	struct inode *inode;
 	struct filename *pathname;
 	int err, found = 0;
+	unsigned int type;
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
@@ -2658,7 +2659,8 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 
 	mapping = victim->f_mapping;
 	spin_lock(&swap_lock);
-	plist_for_each_entry(p, &swap_active_head, list) {
+	for (type = 0; type < nr_swapfiles; type++) {
+		p = swap_info[type];
 		if (p->flags & SWP_WRITEOK) {
 			if (p->swap_file->f_mapping == mapping) {
 				found = 1;
-- 
2.41.0