mm: frontswap: split out __frontswap_curr_pages

Code was duplicated in two functions, clean it up.

Also, assert that the deduplicated code runs under the swap spinlock.
Reviewed-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

mm/frontswap.c

@@ -216,6 +216,20 @@ void __frontswap_invalidate_area(unsigned type)
 }
 EXPORT_SYMBOL(__frontswap_invalidate_area);
 
+static unsigned long __frontswap_curr_pages(void)
+{
+	int type;
+	unsigned long totalpages = 0;
+	struct swap_info_struct *si = NULL;
+
+	assert_spin_locked(&swap_lock);
+	for (type = swap_list.head; type >= 0; type = si->next) {
+		si = swap_info[type];
+		totalpages += atomic_read(&si->frontswap_pages);
+	}
+	return totalpages;
+}
+
 /*
  * Frontswap, like a true swap device, may unnecessarily retain pages
  * under certain circumstances; "shrink" frontswap is essentially a
@@ -240,11 +254,7 @@ void frontswap_shrink(unsigned long target_pages)
 	 */
 	spin_lock(&swap_lock);
 	locked = true;
-	total_pages = 0;
-	for (type = swap_list.head; type >= 0; type = si->next) {
-		si = swap_info[type];
-		total_pages += atomic_read(&si->frontswap_pages);
-	}
+	total_pages = __frontswap_curr_pages();
 	if (total_pages <= target_pages)
 		goto out;
 	total_pages_to_unuse = total_pages - target_pages;
@@ -282,16 +292,12 @@ EXPORT_SYMBOL(frontswap_shrink);
  */
 unsigned long frontswap_curr_pages(void)
 {
-	int type;
 	unsigned long totalpages = 0;
-	struct swap_info_struct *si = NULL;
 
 	spin_lock(&swap_lock);
-	for (type = swap_list.head; type >= 0; type = si->next) {
-		si = swap_info[type];
-		totalpages += atomic_read(&si->frontswap_pages);
-	}
+	totalpages = __frontswap_curr_pages();
 	spin_unlock(&swap_lock);
+
 	return totalpages;
 }
 EXPORT_SYMBOL(frontswap_curr_pages);