[PATCH v3 1/3] btrfs: discard relocated block groups

[Johannes Thumshirn]

When relocating a block group the freed up space is not discarded. On
devices like SSDs this hint is useful to tell the device the space is
freed now. On zoned block devices btrfs' discard code will reset the zone
the block group is on, freeing up the occupied space.

Signed-off-by: Johannes Thumshirn <johannes.thumsh...@wdc.com>
---
 fs/btrfs/volumes.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 6d9b2369f17a..d9ef8bce0cde 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3103,6 +3103,10 @@ static int btrfs_relocate_chunk(struct btrfs_fs_info 
*fs_info, u64 chunk_offset)
        struct btrfs_root *root = fs_info->chunk_root;
        struct btrfs_trans_handle *trans;
        struct btrfs_block_group *block_group;
+       const bool trim = btrfs_is_zoned(fs_info) ||
+                               btrfs_test_opt(fs_info, DISCARD_SYNC);
+       u64 trimmed;
+       u64 length;
        int ret;
 
        /*
@@ -3130,6 +3134,7 @@ static int btrfs_relocate_chunk(struct btrfs_fs_info 
*fs_info, u64 chunk_offset)
        if (!block_group)
                return -ENOENT;
        btrfs_discard_cancel_work(&fs_info->discard_ctl, block_group);
+       length = block_group->length;
        btrfs_put_block_group(block_group);
 
        trans = btrfs_start_trans_remove_block_group(root->fs_info,
@@ -3144,6 +3149,14 @@ static int btrfs_relocate_chunk(struct btrfs_fs_info 
*fs_info, u64 chunk_offset)
         * step two, delete the device extents and the
         * chunk tree entries
         */
+       if (trim) {
+               ret = btrfs_discard_extent(fs_info, chunk_offset, length,
+                                          &trimmed);
+               if (ret) {
+                       btrfs_abort_transaction(trans, ret);
+                       return ret;
+               }
+       }
        ret = btrfs_remove_chunk(trans, chunk_offset);
        btrfs_end_transaction(trans);
        return ret;
-- 
2.30.0