Btrfs: don't preallocate metadata blocks during btrfs_search_slot

In order to avoid doing expensive extent management with tree locks held,
btrfs_search_slot will preallocate tree blocks for use by COW without
any tree locks held.

A later commit moves all of the extent allocation work for COW into
a delayed update mechanism, and this preallocation will no longer be
required.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 18 insertions, 82 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 37f31b5529aa..87c90387283b 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -254,18 +254,13 @@ int btrfs_copy_root(struct btrfs_trans_handle *trans,
  * empty_size -- a hint that you plan on doing more cow.  This is the size in
  * bytes the allocator should try to find free next to the block it returns.
  * This is just a hint and may be ignored by the allocator.
- *
- * prealloc_dest -- if you have already reserved a destination for the cow,
- * this uses that block instead of allocating a new one.
- * btrfs_alloc_reserved_extent is used to finish the allocation.
  */
 static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans,
                              struct btrfs_root *root,
                              struct extent_buffer *buf,
                              struct extent_buffer *parent, int parent_slot,
                              struct extent_buffer **cow_ret,
-                             u64 search_start, u64 empty_size,
-                             u64 prealloc_dest)
+                             u64 search_start, u64 empty_size)
 {
         u64 parent_start;
         struct extent_buffer *cow;
@@ -291,26 +286,10 @@ static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans,
         level = btrfs_header_level(buf);
         nritems = btrfs_header_nritems(buf);
 
-        if (prealloc_dest) {
-                struct btrfs_key ins;
-
-                ins.objectid = prealloc_dest;
-                ins.offset = buf->len;
-                ins.type = BTRFS_EXTENT_ITEM_KEY;
-
-                ret = btrfs_alloc_reserved_extent(trans, root, parent_start,
-                                                  root->root_key.objectid,
-                                                  trans->transid, level, &ins);
-                BUG_ON(ret);
-                cow = btrfs_init_new_buffer(trans, root, prealloc_dest,
-                                            buf->len, level);
-        } else {
-                cow = btrfs_alloc_free_block(trans, root, buf->len,
-                                             parent_start,
-                                             root->root_key.objectid,
-                                             trans->transid, level,
-                                             search_start, empty_size);
-        }
+        cow = btrfs_alloc_free_block(trans, root, buf->len,
+                                     parent_start, root->root_key.objectid,
+                                     trans->transid, level,
+                                     search_start, empty_size);
         if (IS_ERR(cow))
                 return PTR_ERR(cow);
 
@@ -413,7 +392,7 @@ static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans,
 noinline int btrfs_cow_block(struct btrfs_trans_handle *trans,
                     struct btrfs_root *root, struct extent_buffer *buf,
                     struct extent_buffer *parent, int parent_slot,
-                    struct extent_buffer **cow_ret, u64 prealloc_dest)
+                    struct extent_buffer **cow_ret)
 {
         u64 search_start;
         int ret;
@@ -436,7 +415,6 @@ noinline int btrfs_cow_block(struct btrfs_trans_handle *trans,
             btrfs_header_owner(buf) == root->root_key.objectid &&
             !btrfs_header_flag(buf, BTRFS_HEADER_FLAG_WRITTEN)) {
                 *cow_ret = buf;
-                WARN_ON(prealloc_dest);
                 return 0;
         }
 
@@ -447,8 +425,7 @@ noinline int btrfs_cow_block(struct btrfs_trans_handle *trans,
         btrfs_set_lock_blocking(buf);
 
         ret = __btrfs_cow_block(trans, root, buf, parent,
-                                 parent_slot, cow_ret, search_start, 0,
-                                 prealloc_dest);
+                                 parent_slot, cow_ret, search_start, 0);
         return ret;
 }
 
@@ -617,7 +594,7 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans,
                 err = __btrfs_cow_block(trans, root, cur, parent, i,
                                         &cur, search_start,
                                         min(16 * blocksize,
-                                            (end_slot - i) * blocksize), 0);
+                                            (end_slot - i) * blocksize));
                 if (err) {
                         btrfs_tree_unlock(cur);
                         free_extent_buffer(cur);
@@ -937,7 +914,7 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
                 BUG_ON(!child);
                 btrfs_tree_lock(child);
                 btrfs_set_lock_blocking(child);
-                ret = btrfs_cow_block(trans, root, child, mid, 0, &child, 0);
+                ret = btrfs_cow_block(trans, root, child, mid, 0, &child);
                 BUG_ON(ret);
 
                 spin_lock(&root->node_lock);
@@ -979,7 +956,7 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
                 btrfs_tree_lock(left);
                 btrfs_set_lock_blocking(left);
                 wret = btrfs_cow_block(trans, root, left,
-                                       parent, pslot - 1, &left, 0);
+                                       parent, pslot - 1, &left);
                 if (wret) {
                         ret = wret;
                         goto enospc;
@@ -990,7 +967,7 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
                 btrfs_tree_lock(right);
                 btrfs_set_lock_blocking(right);
                 wret = btrfs_cow_block(trans, root, right,
-                                       parent, pslot + 1, &right, 0);
+                                       parent, pslot + 1, &right);
                 if (wret) {
                         ret = wret;
                         goto enospc;
@@ -1171,7 +1148,7 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
                         wret = 1;
                 } else {
                         ret = btrfs_cow_block(trans, root, left, parent,
-                                              pslot - 1, &left, 0);
+                                              pslot - 1, &left);
                         if (ret)
                                 wret = 1;
                         else {
@@ -1222,7 +1199,7 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
                 } else {
                         ret = btrfs_cow_block(trans, root, right,
                                               parent, pslot + 1,
-                                              &right, 0);
+                                              &right);
                         if (ret)
                                 wret = 1;
                         else {
@@ -1492,7 +1469,6 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root
         u8 lowest_level = 0;
         u64 blocknr;
         u64 gen;
-        struct btrfs_key prealloc_block;
 
         lowest_level = p->lowest_level;
         WARN_ON(lowest_level && ins_len > 0);
@@ -1501,8 +1477,6 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root
         if (ins_len < 0)
                 lowest_unlock = 2;
 
-        prealloc_block.objectid = 0;
-
 again:
         if (p->skip_locking)
                 b = btrfs_root_node(root);
@@ -1529,44 +1503,11 @@ again:
                             !btrfs_header_flag(b, BTRFS_HEADER_FLAG_WRITTEN)) {
                                 goto cow_done;
                         }
-
-                        /* ok, we have to cow, is our old prealloc the right
-                         * size?
-                         */
-                        if (prealloc_block.objectid &&
-                            prealloc_block.offset != b->len) {
-                                btrfs_release_path(root, p);
-                                btrfs_free_reserved_extent(root,
-                                           prealloc_block.objectid,
-                                           prealloc_block.offset);
-                                prealloc_block.objectid = 0;
-                                goto again;
-                        }
-
-                        /*
-                         * for higher level blocks, try not to allocate blocks
-                         * with the block and the parent locks held.
-                         */
-                        if (level > 0 && !prealloc_block.objectid) {
-                                u32 size = b->len;
-                                u64 hint = b->start;
-
-                                btrfs_release_path(root, p);
-                                ret = btrfs_reserve_extent(trans, root,
-                                                           size, size, 0,
-                                                           hint, (u64)-1,
-                                                           &prealloc_block, 0);
-                                BUG_ON(ret);
-                                goto again;
-                        }
-
                         btrfs_set_path_blocking(p);
 
                         wret = btrfs_cow_block(trans, root, b,
                                                p->nodes[level + 1],
-                                               p->slots[level + 1],
-                                               &b, prealloc_block.objectid);
-                        prealloc_block.objectid = 0;
+                                               p->slots[level + 1], &b);
                         if (wret) {
                                 free_extent_buffer(b);
                                 ret = wret;
@@ -1743,11 +1684,6 @@ done:
          * from here on, so for now just mark it as blocking
          */
         btrfs_set_path_blocking(p);
-        if (prealloc_block.objectid) {
-                btrfs_free_reserved_extent(root,
-                           prealloc_block.objectid,
-                           prealloc_block.offset);
-        }
         return ret;
 }
 
@@ -1768,7 +1704,7 @@ int btrfs_merge_path(struct btrfs_trans_handle *trans,
         int ret;
 
         eb = btrfs_lock_root_node(root);
-        ret = btrfs_cow_block(trans, root, eb, NULL, 0, &eb, 0);
+        ret = btrfs_cow_block(trans, root, eb, NULL, 0, &eb);
         BUG_ON(ret);
 
         btrfs_set_lock_blocking(eb);
@@ -1826,7 +1762,7 @@ int btrfs_merge_path(struct btrfs_trans_handle *trans,
                         }
 
                         ret = btrfs_cow_block(trans, root, eb, parent, slot,
-                                              &eb, 0);
+                                              &eb);
                         BUG_ON(ret);
 
                         if (root->root_key.objectid ==
@@ -2377,7 +2313,7 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
 
         /* cow and double check */
         ret = btrfs_cow_block(trans, root, right, upper,
-                              slot + 1, &right, 0);
+                              slot + 1, &right);
         if (ret)
                 goto out_unlock;
 
@@ -2576,7 +2512,7 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
 
         /* cow and double check */
         ret = btrfs_cow_block(trans, root, left,
-                              path->nodes[1], slot - 1, &left, 0);
+                              path->nodes[1], slot - 1, &left);
         if (ret) {
                 /* we hit -ENOSPC, but it isn't fatal here */
                 ret = 1;