btrfs: relocation: Check cancel request after each data page read

When relocating a data extents with large large data extents, we spend
most of our time in relocate_file_extent_cluster() at stage "moving data
extents":

 1)               |  btrfs_relocate_block_group [btrfs]() {
 1)               |    relocate_file_extent_cluster [btrfs]() {
 1) $ 6586769 us  |    }
 1) + 18.260 us   |    relocate_file_extent_cluster [btrfs]();
 1) + 15.770 us   |    relocate_file_extent_cluster [btrfs]();
 1) $ 8916340 us  |  }
 1)               |  btrfs_relocate_block_group [btrfs]() {
 1)               |    relocate_file_extent_cluster [btrfs]() {
 1) $ 11611586 us |    }
 1) + 16.930 us   |    relocate_file_extent_cluster [btrfs]();
 1) + 15.870 us   |    relocate_file_extent_cluster [btrfs]();
 1) $ 14986130 us |  }

To make data relocation cancelling quicker, add extra balance cancelling
check after each page read in relocate_file_extent_cluster().

Cleanup and error handling uses the same mechanism as if the whole
process finished

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 0238801..a4edb82 100644 (file)
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -3445,6 +3445,10 @@ static int relocate_file_extent_cluster(struct inode *inode,
                btrfs_delalloc_release_extents(BTRFS_I(inode), PAGE_SIZE);
                balance_dirty_pages_ratelimited(inode->i_mapping);
                btrfs_throttle(fs_info);
+               if (btrfs_should_cancel_balance(fs_info)) {
+                       ret = -ECANCELED;
+                       goto out;
+               }
        }
        WARN_ON(nr != cluster->nr);
 out:
@@ -4259,6 +4263,14 @@ restart:
        backref_cache_cleanup(&rc->backref_cache);
        btrfs_block_rsv_release(fs_info, rc->block_rsv, (u64)-1);
 
+       /*
+        * Even in the case when the relocation is cancelled, we should all go
+        * through prepare_to_merge() and merge_reloc_roots().
+        *
+        * For error (including cancelled balance), prepare_to_merge() will
+        * mark all reloc trees orphan, then queue them for cleanup in
+        * merge_reloc_roots()
+        */
        err = prepare_to_merge(rc, err);
 
        merge_reloc_roots(rc);