Btrfs: optimize how we account for space in truncate

Currently we're starting and stopping a transaction for no real reason, so kill
that and just reserve enough space as if we can truncate all in one transaction.
Also use btrfs_block_rsv_check() for our reserve to minimize the amount of space
we may have to allocate for our slack space.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>

1 files changed, 29 insertions, 29 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index fe3891e240b3..4d057c084de6 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -6482,6 +6482,7 @@ static int btrfs_truncate(struct inode *inode)
         struct btrfs_trans_handle *trans;
         unsigned long nr;
         u64 mask = root->sectorsize - 1;
+        u64 min_size = btrfs_calc_trans_metadata_size(root, 2);
 
         ret = btrfs_truncate_page(inode->i_mapping, inode->i_size);
         if (ret)
@@ -6530,17 +6531,21 @@ static int btrfs_truncate(struct inode *inode)
         if (!rsv)
                 return -ENOMEM;
 
-        trans = btrfs_start_transaction(root, 4);
+        /*
+         * 2 for the truncate slack space
+         * 1 for the orphan item we're going to add
+         * 1 for the orphan item deletion
+         * 1 for updating the inode.
+         */
+        trans = btrfs_start_transaction(root, 5);
         if (IS_ERR(trans)) {
                 err = PTR_ERR(trans);
                 goto out;
         }
 
-        /*
-         * Reserve space for the truncate process.  Truncate should be adding
-         * space, but if there are snapshots it may end up using space.
-         */
-        ret = btrfs_truncate_reserve_metadata(trans, root, rsv);
+        /* Migrate the slack space for the truncate to our reserve */
+        ret = btrfs_block_rsv_migrate(&root->fs_info->trans_block_rsv, rsv,
+                                      min_size);
         BUG_ON(ret);
 
         ret = btrfs_orphan_add(trans, inode);
@@ -6549,21 +6554,6 @@ static int btrfs_truncate(struct inode *inode)
                 goto out;
         }
 
-        nr = trans->blocks_used;
-        btrfs_end_transaction(trans, root);
-        btrfs_btree_balance_dirty(root, nr);
-
-        /*
-         * Ok so we've already migrated our bytes over for the truncate, so here
-         * just reserve the one slot we need for updating the inode.
-         */
-        trans = btrfs_start_transaction(root, 1);
-        if (IS_ERR(trans)) {
-                err = PTR_ERR(trans);
-                goto out;
-        }
-        trans->block_rsv = rsv;
-
         /*
          * setattr is responsible for setting the ordered_data_close flag,
          * but that is only tested during the last file release.  That
@@ -6585,20 +6575,30 @@ static int btrfs_truncate(struct inode *inode)
                 btrfs_add_ordered_operation(trans, root, inode);
 
         while (1) {
+                ret = btrfs_block_rsv_check(trans, root, rsv, min_size, 0);
+                if (ret) {
+                        /*
+                         * This can only happen with the original transaction we
+                         * started above, every other time we shouldn't have a
+                         * transaction started yet.
+                         */
+                        if (ret == -EAGAIN)
+                                goto end_trans;
+                        err = ret;
+                        break;
+                }
+
                 if (!trans) {
-                        trans = btrfs_start_transaction(root, 3);
+                        /* Just need the 1 for updating the inode */
+                        trans = btrfs_start_transaction(root, 1);
                         if (IS_ERR(trans)) {
                                 err = PTR_ERR(trans);
                                 goto out;
                         }
-
-                        ret = btrfs_truncate_reserve_metadata(trans, root,
-                                                              rsv);
-                        BUG_ON(ret);
-
-                        trans->block_rsv = rsv;
                 }
 
+                trans->block_rsv = rsv;
+
                 ret = btrfs_truncate_inode_items(trans, root, inode,
                                                  inode->i_size,
                                                  BTRFS_EXTENT_DATA_KEY);
@@ -6613,7 +6613,7 @@ static int btrfs_truncate(struct inode *inode)
                         err = ret;
                         break;
                 }
-
+end_trans:
                 nr = trans->blocks_used;
                 btrfs_end_transaction(trans, root);
                 trans = NULL;