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btrfs: handle free space tree rebuild in multiple transactions

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During free space tree rebuild, we're holding a transaction handle for
the whole rebuild process.

This can lead to blocked task warning, e.g. btrfs-transaction kthread
(which is already created before btrfs_start_pre_rw_mount()) can be
waked up to join and commit the current transaction.

But the free space tree rebuild process may need to go through thousands
block groups, this will block btrfs-transaction kthread for a long time.

Fix the problem by calling btrfs_should_end_transaction() after each
block group, so that we won't hold the transaction handle too long.

And since the free-space-tree rebuild can be split into
multiple transactions, we need to consider the safety when the rebuild
process is interrupted.

Thankfully since we only set the FREE_SPACE_TREE compat_ro flag without
FREE_SPACE_TREE_VALID flag, even if the rebuild is interrupted, on the
next RW mount, we will still go rebuild the free space tree, by deleting
any items we have and re-starting the rebuild from scratch.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Qu Wenruo 2024-12-19 15:04:08 +10:30 • committed by David Sterba
parent 6a2b3d7a36
commit 882af9f13e
1 changed files with 6 additions and 0 deletions
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6
fs/btrfs/free-space-tree.c
View file

@ -1350,6 +1350,12 @@ int btrfs_rebuild_free_space_tree(struct btrfs_fs_info *fs_info)
btrfs_end_transaction(trans);
return ret;
}
if (btrfs_should_end_transaction(trans)) {
btrfs_end_transaction(trans);
trans = btrfs_start_transaction(free_space_root, 1);
if (IS_ERR(trans))
return PTR_ERR(trans);
}
node = rb_next(node);
}