btrfs: restructure find_free_dev_extent()

- make it return the start position and length of the max free space when it can
  not find a suitable free space.
- make it more readability

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 3c71d95..1e1c9a1 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -8099,7 +8099,7 @@ int btrfs_can_relocate(struct btrfs_root *root, u64 bytenr)
        mutex_lock(&root->fs_info->chunk_mutex);
        list_for_each_entry(device, &fs_devices->alloc_list, dev_alloc_list) {
                u64 min_free = btrfs_block_group_used(&block_group->item);
-               u64 dev_offset, max_avail;
+               u64 dev_offset;
 
                /*
                 * check to make sure we can actually find a chunk with enough
@@ -8107,7 +8107,7 @@ int btrfs_can_relocate(struct btrfs_root *root, u64 bytenr)
                 */
                if (device->total_bytes > device->bytes_used + min_free) {
                        ret = find_free_dev_extent(NULL, device, min_free,
-                                                  &dev_offset, &max_avail);
+                                                  &dev_offset, NULL);
                        if (!ret)
                                break;
                        ret = -1;

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index c50a85e..4838bd3 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -729,58 +729,82 @@ error:
 }
 
 /*
+ * find_free_dev_extent - find free space in the specified device
+ * @trans:     transaction handler
+ * @device:    the device which we search the free space in
+ * @num_bytes: the size of the free space that we need
+ * @start:     store the start of the free space.
+ * @len:       the size of the free space. that we find, or the size of the max
+ *             free space if we don't find suitable free space
+ *
  * this uses a pretty simple search, the expectation is that it is
  * called very infrequently and that a given device has a small number
  * of extents
+ *
+ * @start is used to store the start of the free space if we find. But if we
+ * don't find suitable free space, it will be used to store the start position
+ * of the max free space.
+ *
+ * @len is used to store the size of the free space that we find.
+ * But if we don't find suitable free space, it is used to store the size of
+ * the max free space.
  */
 int find_free_dev_extent(struct btrfs_trans_handle *trans,
                         struct btrfs_device *device, u64 num_bytes,
-                        u64 *start, u64 *max_avail)
+                        u64 *start, u64 *len)
 {
        struct btrfs_key key;
        struct btrfs_root *root = device->dev_root;
-       struct btrfs_dev_extent *dev_extent = NULL;
+       struct btrfs_dev_extent *dev_extent;
        struct btrfs_path *path;
-       u64 hole_size = 0;
-       u64 last_byte = 0;
-       u64 search_start = 0;
+       u64 hole_size;
+       u64 max_hole_start;
+       u64 max_hole_size;
+       u64 extent_end;
+       u64 search_start;
        u64 search_end = device->total_bytes;
        int ret;
-       int slot = 0;
-       int start_found;
+       int slot;
        struct extent_buffer *l;
 
-       path = btrfs_alloc_path();
-       if (!path)
-               return -ENOMEM;
-       path->reada = 2;
-       start_found = 0;
-
        /* FIXME use last free of some kind */
 
        /* we don't want to overwrite the superblock on the drive,
         * so we make sure to start at an offset of at least 1MB
         */
-       search_start = max((u64)1024 * 1024, search_start);
+       search_start = 1024 * 1024;
 
-       if (root->fs_info->alloc_start + num_bytes <= device->total_bytes)
+       if (root->fs_info->alloc_start + num_bytes <= search_end)
                search_start = max(root->fs_info->alloc_start, search_start);
 
+       max_hole_start = search_start;
+       max_hole_size = 0;
+
+       if (search_start >= search_end) {
+               ret = -ENOSPC;
+               goto error;
+       }
+
+       path = btrfs_alloc_path();
+       if (!path) {
+               ret = -ENOMEM;
+               goto error;
+       }
+       path->reada = 2;
+
        key.objectid = device->devid;
        key.offset = search_start;
        key.type = BTRFS_DEV_EXTENT_KEY;
+
        ret = btrfs_search_slot(trans, root, &key, path, 0, 0);
        if (ret < 0)
-               goto error;
+               goto out;
        if (ret > 0) {
                ret = btrfs_previous_item(root, path, key.objectid, key.type);
                if (ret < 0)
-                       goto error;
-               if (ret > 0)
-                       start_found = 1;
+                       goto out;
        }
-       l = path->nodes[0];
-       btrfs_item_key_to_cpu(l, &key, path->slots[0]);
+
        while (1) {
                l = path->nodes[0];
                slot = path->slots[0];
@@ -789,24 +813,9 @@ int find_free_dev_extent(struct btrfs_trans_handle *trans,
                        if (ret == 0)
                                continue;
                        if (ret < 0)
-                               goto error;
-no_more_items:
-                       if (!start_found) {
-                               if (search_start >= search_end) {
-                                       ret = -ENOSPC;
-                                       goto error;
-                               }
-                               *start = search_start;
-                               start_found = 1;
-                               goto check_pending;
-                       }
-                       *start = last_byte > search_start ?
-                               last_byte : search_start;
-                       if (search_end <= *start) {
-                               ret = -ENOSPC;
-                               goto error;
-                       }
-                       goto check_pending;
+                               goto out;
+
+                       break;
                }
                btrfs_item_key_to_cpu(l, &key, slot);
 
@@ -814,48 +823,62 @@ no_more_items:
                        goto next;
 
                if (key.objectid > device->devid)
-                       goto no_more_items;
+                       break;
 
-               if (key.offset >= search_start && key.offset > last_byte &&
-                   start_found) {
-                       if (last_byte < search_start)
-                               last_byte = search_start;
-                       hole_size = key.offset - last_byte;
+               if (btrfs_key_type(&key) != BTRFS_DEV_EXTENT_KEY)
+                       goto next;
 
-                       if (hole_size > *max_avail)
-                               *max_avail = hole_size;
+               if (key.offset > search_start) {
+                       hole_size = key.offset - search_start;
 
-                       if (key.offset > last_byte &&
-                           hole_size >= num_bytes) {
-                               *start = last_byte;
-                               goto check_pending;
+                       if (hole_size > max_hole_size) {
+                               max_hole_start = search_start;
+                               max_hole_size = hole_size;
+                       }
+
+                       /*
+                        * If this free space is greater than which we need,
+                        * it must be the max free space that we have found
+                        * until now, so max_hole_start must point to the start
+                        * of this free space and the length of this free space
+                        * is stored in max_hole_size. Thus, we return
+                        * max_hole_start and max_hole_size and go back to the
+                        * caller.
+                        */
+                       if (hole_size >= num_bytes) {
+                               ret = 0;
+                               goto out;
                        }
                }
-               if (btrfs_key_type(&key) != BTRFS_DEV_EXTENT_KEY)
-                       goto next;
 
-               start_found = 1;
                dev_extent = btrfs_item_ptr(l, slot, struct btrfs_dev_extent);
-               last_byte = key.offset + btrfs_dev_extent_length(l, dev_extent);
+               extent_end = key.offset + btrfs_dev_extent_length(l,
+                                                                 dev_extent);
+               if (extent_end > search_start)
+                       search_start = extent_end;
 next:
                path->slots[0]++;
                cond_resched();
        }
-check_pending:
-       /* we have to make sure we didn't find an extent that has already
-        * been allocated by the map tree or the original allocation
-        */
-       BUG_ON(*start < search_start);
 
-       if (*start + num_bytes > search_end) {
-               ret = -ENOSPC;
-               goto error;
+       hole_size = search_end- search_start;
+       if (hole_size > max_hole_size) {
+               max_hole_start = search_start;
+               max_hole_size = hole_size;
        }
-       /* check for pending inserts here */
-       ret = 0;
 
-error:
+       /* See above. */
+       if (hole_size < num_bytes)
+               ret = -ENOSPC;
+       else
+               ret = 0;
+
+out:
        btrfs_free_path(path);
+error:
+       *start = max_hole_start;
+       if (len && max_hole_size > *len)
+               *len = max_hole_size;
        return ret;
 }