Btrfs: use a slab for ordered extents allocation

The ordered extent allocation is in the fast path of the IO, so use a slab
to improve the speed of the allocation.

 "Size of the struct is 280, so this will fall into the size-512 bucket,
  giving 8 objects per page, while own slab will pack 14 objects into a page.

  Another benefit I see is to check for leaked objects when the module is
  removed (and the cache destroy takes place)."
						-- David Sterba
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>

fs/btrfs/ordered-data.c

@@ -25,6 +25,8 @@
 #include "btrfs_inode.h"
 #include "extent_io.h"
 
+static struct kmem_cache *btrfs_ordered_extent_cache;
+
 static u64 entry_end(struct btrfs_ordered_extent *entry)
 {
 	if (entry->file_offset + entry->len < entry->file_offset)
@@ -187,7 +189,7 @@ static int __btrfs_add_ordered_extent(struct inode *inode, u64 file_offset,
 	struct btrfs_ordered_extent *entry;
 
 	tree = &BTRFS_I(inode)->ordered_tree;
-	entry = kzalloc(sizeof(*entry), GFP_NOFS);
+	entry = kmem_cache_zalloc(btrfs_ordered_extent_cache, GFP_NOFS);
 	if (!entry)
 		return -ENOMEM;
 
@@ -421,7 +423,7 @@ void btrfs_put_ordered_extent(struct btrfs_ordered_extent *entry)
 			list_del(&sum->list);
 			kfree(sum);
 		}
-		kfree(entry);
+		kmem_cache_free(btrfs_ordered_extent_cache, entry);
 	}
 }
 
@@ -958,3 +960,20 @@ void btrfs_add_ordered_operation(struct btrfs_trans_handle *trans,
 	}
 	spin_unlock(&root->fs_info->ordered_extent_lock);
 }
+
+int __init ordered_data_init(void)
+{
+	btrfs_ordered_extent_cache = kmem_cache_create("btrfs_ordered_extent",
+				     sizeof(struct btrfs_ordered_extent), 0,
+				     SLAB_RECLAIM_ACCOUNT | SLAB_MEM_SPREAD,
+				     NULL);
+	if (!btrfs_ordered_extent_cache)
+		return -ENOMEM;
+	return 0;
+}
+
+void ordered_data_exit(void)
+{
+	if (btrfs_ordered_extent_cache)
+		kmem_cache_destroy(btrfs_ordered_extent_cache);
+}

fs/btrfs/ordered-data.h

@@ -192,4 +192,6 @@ void btrfs_add_ordered_operation(struct btrfs_trans_handle *trans,
 				 struct inode *inode);
 void btrfs_wait_ordered_extents(struct btrfs_root *root,
 				int nocow_only, int delay_iput);
+int __init ordered_data_init(void);
+void ordered_data_exit(void);
 #endif

fs/btrfs/super.c

@@ -1620,10 +1620,14 @@ static int __init init_btrfs_fs(void)
 	if (err)
 		goto free_extent_io;
 
-	err = btrfs_delayed_inode_init();
+	err = ordered_data_init();
 	if (err)
 		goto free_extent_map;
 
+	err = btrfs_delayed_inode_init();
+	if (err)
+		goto free_ordered_data;
+
 	err = btrfs_interface_init();
 	if (err)
 		goto free_delayed_inode;
@@ -1641,6 +1645,8 @@ static int __init init_btrfs_fs(void)
 	btrfs_interface_exit();
 free_delayed_inode:
 	btrfs_delayed_inode_exit();
+free_ordered_data:
+	ordered_data_exit();
 free_extent_map:
 	extent_map_exit();
 free_extent_io:
@@ -1657,6 +1663,7 @@ static void __exit exit_btrfs_fs(void)
 {
 	btrfs_destroy_cachep();
 	btrfs_delayed_inode_exit();
+	ordered_data_exit();
 	extent_map_exit();
 	extent_io_exit();
 	btrfs_interface_exit();