2 files changed, 38 insertions, 2 deletions

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 9cabb8b21aba..0b9210ea96c7 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -120,6 +120,7 @@ struct swap_extent {
 enum {
         SWP_USED        = (1 << 0),     /* is slot in swap_info[] used? */
         SWP_WRITEOK     = (1 << 1),     /* ok to write to this swap?    */
+        SWP_DISCARDABLE = (1 << 2),     /* blkdev supports discard */
                                         /* add others here before... */
         SWP_SCANNING    = (1 << 8),     /* refcount in scan_swap_map */
 };
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 4d9855f86e7d..fbeb4bb8eb50 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -84,6 +84,37 @@ void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page)
         up_read(&swap_unplug_sem);
 }
 
+/*
+ * swapon tell device that all the old swap contents can be discarded,
+ * to allow the swap device to optimize its wear-levelling.
+ */
+static int discard_swap(struct swap_info_struct *si)
+{
+        struct swap_extent *se;
+        int err = 0;
+
+        list_for_each_entry(se, &si->extent_list, list) {
+                sector_t start_block = se->start_block << (PAGE_SHIFT - 9);
+                pgoff_t nr_blocks = se->nr_pages << (PAGE_SHIFT - 9);
+
+                if (se->start_page == 0) {
+                        /* Do not discard the swap header page! */
+                        start_block += 1 << (PAGE_SHIFT - 9);
+                        nr_blocks -= 1 << (PAGE_SHIFT - 9);
+                        if (!nr_blocks)
+                                continue;
+                }
+
+                err = blkdev_issue_discard(si->bdev, start_block,
+                                                nr_blocks, GFP_KERNEL);
+                if (err)
+                        break;
+
+                cond_resched();
+        }
+        return err;             /* That will often be -EOPNOTSUPP */
+}
+
 #define SWAPFILE_CLUSTER        256
 #define LATENCY_LIMIT           256
 
@@ -1658,6 +1689,9 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
                 goto bad_swap;
         }
 
+        if (discard_swap(p) == 0)
+                p->flags |= SWP_DISCARDABLE;
+
         mutex_lock(&swapon_mutex);
         spin_lock(&swap_lock);
         if (swap_flags & SWAP_FLAG_PREFER)
@@ -1671,9 +1705,10 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
         total_swap_pages += nr_good_pages;
 
         printk(KERN_INFO "Adding %uk swap on %s.  "
-                        "Priority:%d extents:%d across:%lluk\n",
+                        "Priority:%d extents:%d across:%lluk%s\n",
                 nr_good_pages<<(PAGE_SHIFT-10), name, p->prio,
-                nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10));
+                nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
+                (p->flags & SWP_DISCARDABLE) ? " D" : "");
 
         /* insert swap space into swap_list: */
         prev = -1;