mm: frontswap: split out __frontswap_unuse_pages

An attempt at making frontswap_shrink shorter and more readable. This patch
splits out walking through the swap list to find an entry with enough
pages to unuse.

Also, assert that the internal __frontswap_unuse_pages is called under swap
lock, since that part of code was previously directly happen inside the lock.

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

1 files changed, 39 insertions, 20 deletions

diff --git a/mm/frontswap.c b/mm/frontswap.c
index 5faf840f8726..faa43b7eea6f 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -230,6 +230,41 @@ static unsigned long __frontswap_curr_pages(void)
         return totalpages;
 }
 
+static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
+                                        int *swapid)
+{
+        int ret = -EINVAL;
+        struct swap_info_struct *si = NULL;
+        int si_frontswap_pages;
+        unsigned long total_pages_to_unuse = total;
+        unsigned long pages = 0, pages_to_unuse = 0;
+        int type;
+
+        assert_spin_locked(&swap_lock);
+        for (type = swap_list.head; type >= 0; type = si->next) {
+                si = swap_info[type];
+                si_frontswap_pages = atomic_read(&si->frontswap_pages);
+                if (total_pages_to_unuse < si_frontswap_pages) {
+                        pages = pages_to_unuse = total_pages_to_unuse;
+                } else {
+                        pages = si_frontswap_pages;
+                        pages_to_unuse = 0; /* unuse all */
+                }
+                /* ensure there is enough RAM to fetch pages from frontswap */
+                if (security_vm_enough_memory_mm(current->mm, pages)) {
+                        ret = -ENOMEM;
+                        continue;
+                }
+                vm_unacct_memory(pages);
+                *unused = pages_to_unuse;
+                *swapid = type;
+                ret = 0;
+                break;
+        }
+
+        return ret;
+}
+
 /*
  * Frontswap, like a true swap device, may unnecessarily retain pages
  * under certain circumstances; "shrink" frontswap is essentially a
@@ -240,11 +275,9 @@ static unsigned long __frontswap_curr_pages(void)
  */
 void frontswap_shrink(unsigned long target_pages)
 {
-        struct swap_info_struct *si = NULL;
-        int si_frontswap_pages;
         unsigned long total_pages = 0, total_pages_to_unuse;
-        unsigned long pages = 0, pages_to_unuse = 0;
-        int type;
+        unsigned long pages_to_unuse = 0;
+        int type, ret;
         bool locked = false;
 
         /*
@@ -258,22 +291,8 @@ void frontswap_shrink(unsigned long target_pages)
         if (total_pages <= target_pages)
                 goto out;
         total_pages_to_unuse = total_pages - target_pages;
-        for (type = swap_list.head; type >= 0; type = si->next) {
-                si = swap_info[type];
-                si_frontswap_pages = atomic_read(&si->frontswap_pages);
-                if (total_pages_to_unuse < si_frontswap_pages) {
-                        pages = pages_to_unuse = total_pages_to_unuse;
-                } else {
-                        pages = si_frontswap_pages;
-                        pages_to_unuse = 0; /* unuse all */
-                }
-                /* ensure there is enough RAM to fetch pages from frontswap */
-                if (security_vm_enough_memory_mm(current->mm, pages))
-                        continue;
-                vm_unacct_memory(pages);
-                break;
-        }
-        if (type < 0)
+        ret = __frontswap_unuse_pages(total_pages_to_unuse, &pages_to_unuse, &type);
+        if (ret < 0)
                 goto out;
         locked = false;
         spin_unlock(&swap_lock);