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Linux/fs/btrfs/tree-defrag.c

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  1 /*
  2  * Copyright (C) 2007 Oracle.  All rights reserved.
  3  *
  4  * This program is free software; you can redistribute it and/or
  5  * modify it under the terms of the GNU General Public
  6  * License v2 as published by the Free Software Foundation.
  7  *
  8  * This program is distributed in the hope that it will be useful,
  9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
 10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 11  * General Public License for more details.
 12  *
 13  * You should have received a copy of the GNU General Public
 14  * License along with this program; if not, write to the
 15  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 16  * Boston, MA 021110-1307, USA.
 17  */
 18 
 19 #include <linux/sched.h>
 20 #include "ctree.h"
 21 #include "disk-io.h"
 22 #include "print-tree.h"
 23 #include "transaction.h"
 24 #include "locking.h"
 25 
 26 /*
 27  * Defrag all the leaves in a given btree.
 28  * Read all the leaves and try to get key order to
 29  * better reflect disk order
 30  */
 31 
 32 int btrfs_defrag_leaves(struct btrfs_trans_handle *trans,
 33                         struct btrfs_root *root)
 34 {
 35         struct btrfs_path *path = NULL;
 36         struct btrfs_key key;
 37         int ret = 0;
 38         int wret;
 39         int level;
 40         int next_key_ret = 0;
 41         u64 last_ret = 0;
 42         u64 min_trans = 0;
 43 
 44         if (root->fs_info->extent_root == root) {
 45                 /*
 46                  * there's recursion here right now in the tree locking,
 47                  * we can't defrag the extent root without deadlock
 48                  */
 49                 goto out;
 50         }
 51 
 52         if (!test_bit(BTRFS_ROOT_REF_COWS, &root->state))
 53                 goto out;
 54 
 55         path = btrfs_alloc_path();
 56         if (!path)
 57                 return -ENOMEM;
 58 
 59         level = btrfs_header_level(root->node);
 60 
 61         if (level == 0)
 62                 goto out;
 63 
 64         if (root->defrag_progress.objectid == 0) {
 65                 struct extent_buffer *root_node;
 66                 u32 nritems;
 67 
 68                 root_node = btrfs_lock_root_node(root);
 69                 btrfs_set_lock_blocking(root_node);
 70                 nritems = btrfs_header_nritems(root_node);
 71                 root->defrag_max.objectid = 0;
 72                 /* from above we know this is not a leaf */
 73                 btrfs_node_key_to_cpu(root_node, &root->defrag_max,
 74                                       nritems - 1);
 75                 btrfs_tree_unlock(root_node);
 76                 free_extent_buffer(root_node);
 77                 memset(&key, 0, sizeof(key));
 78         } else {
 79                 memcpy(&key, &root->defrag_progress, sizeof(key));
 80         }
 81 
 82         path->keep_locks = 1;
 83 
 84         ret = btrfs_search_forward(root, &key, path, min_trans);
 85         if (ret < 0)
 86                 goto out;
 87         if (ret > 0) {
 88                 ret = 0;
 89                 goto out;
 90         }
 91         btrfs_release_path(path);
 92         /*
 93          * We don't need a lock on a leaf. btrfs_realloc_node() will lock all
 94          * leafs from path->nodes[1], so set lowest_level to 1 to avoid later
 95          * a deadlock (attempting to write lock an already write locked leaf).
 96          */
 97         path->lowest_level = 1;
 98         wret = btrfs_search_slot(trans, root, &key, path, 0, 1);
 99 
100         if (wret < 0) {
101                 ret = wret;
102                 goto out;
103         }
104         if (!path->nodes[1]) {
105                 ret = 0;
106                 goto out;
107         }
108         /*
109          * The node at level 1 must always be locked when our path has
110          * keep_locks set and lowest_level is 1, regardless of the value of
111          * path->slots[1].
112          */
113         BUG_ON(path->locks[1] == 0);
114         ret = btrfs_realloc_node(trans, root,
115                                  path->nodes[1], 0,
116                                  &last_ret,
117                                  &root->defrag_progress);
118         if (ret) {
119                 WARN_ON(ret == -EAGAIN);
120                 goto out;
121         }
122         /*
123          * Now that we reallocated the node we can find the next key. Note that
124          * btrfs_find_next_key() can release our path and do another search
125          * without COWing, this is because even with path->keep_locks = 1,
126          * btrfs_search_slot() / ctree.c:unlock_up() does not keeps a lock on a
127          * node when path->slots[node_level - 1] does not point to the last
128          * item or a slot beyond the last item (ctree.c:unlock_up()). Therefore
129          * we search for the next key after reallocating our node.
130          */
131         path->slots[1] = btrfs_header_nritems(path->nodes[1]);
132         next_key_ret = btrfs_find_next_key(root, path, &key, 1,
133                                            min_trans);
134         if (next_key_ret == 0) {
135                 memcpy(&root->defrag_progress, &key, sizeof(key));
136                 ret = -EAGAIN;
137         }
138 out:
139         btrfs_free_path(path);
140         if (ret == -EAGAIN) {
141                 if (root->defrag_max.objectid > root->defrag_progress.objectid)
142                         goto done;
143                 if (root->defrag_max.type > root->defrag_progress.type)
144                         goto done;
145                 if (root->defrag_max.offset > root->defrag_progress.offset)
146                         goto done;
147                 ret = 0;
148         }
149 done:
150         if (ret != -EAGAIN) {
151                 memset(&root->defrag_progress, 0,
152                        sizeof(root->defrag_progress));
153                 root->defrag_trans_start = trans->transid;
154         }
155         return ret;
156 }
157 

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