mm: frontswap: split frontswap_shrink further to simplify locking

Split frontswap_shrink to simplify the locking in the original code.

Also, assert that the function that was split still runs under the
swap spinlock.

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

diff --git a/mm/frontswap.c b/mm/frontswap.c
index faa43b7eea6faec163234defc5d7318290a94d6a..e6353d9151eeda274ed87643ee13814f28153ac7 100644 (file)
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -265,6 +265,24 @@ static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
        return ret;
 }
 
+static int __frontswap_shrink(unsigned long target_pages,
+                               unsigned long *pages_to_unuse,
+                               int *type)
+{
+       unsigned long total_pages = 0, total_pages_to_unuse;
+
+       assert_spin_locked(&swap_lock);
+
+       total_pages = __frontswap_curr_pages();
+       if (total_pages <= target_pages) {
+               /* Nothing to do */
+               *pages_to_unuse = 0;
+               return 0;
+       }
+       total_pages_to_unuse = total_pages - target_pages;
+       return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type);
+}
+
 /*
  * Frontswap, like a true swap device, may unnecessarily retain pages
  * under certain circumstances; "shrink" frontswap is essentially a
@@ -275,10 +293,8 @@ static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
  */
 void frontswap_shrink(unsigned long target_pages)
 {
-       unsigned long total_pages = 0, total_pages_to_unuse;
        unsigned long pages_to_unuse = 0;
        int type, ret;
-       bool locked = false;
 
        /*
         * we don't want to hold swap_lock while doing a very
@@ -286,20 +302,10 @@ void frontswap_shrink(unsigned long target_pages)
         * so restart scan from swap_list.head each time
         */
        spin_lock(&swap_lock);
-       locked = true;
-       total_pages = __frontswap_curr_pages();
-       if (total_pages <= target_pages)
-               goto out;
-       total_pages_to_unuse = total_pages - target_pages;
-       ret = __frontswap_unuse_pages(total_pages_to_unuse, &pages_to_unuse, &type);
-       if (ret < 0)
-               goto out;
-       locked = false;
+       ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);
        spin_unlock(&swap_lock);
-       try_to_unuse(type, true, pages_to_unuse);
-out:
-       if (locked)
-               spin_unlock(&swap_lock);
+       if (ret == 0 && pages_to_unuse)
+               try_to_unuse(type, true, pages_to_unuse);
        return;
 }
 EXPORT_SYMBOL(frontswap_shrink);