Re: [PATCH] btrfs: relocation: Output current relocation stage at btrfs_relocate_block_group()

[Su Yue <Damenly_Su@gmx.com>]

On 2019/11/28 3:54 PM, Qu Wenruo wrote:
> There are several reports of hanging relocation, populating the dmesg
> with things like:
>    BTRFS info (device dm-5): found 1 extents
>
> The investigation is still on going, but will never hurt to output a
> little more info.
>
> This patch will also output the current relocation stage, making that
> output something like:
>
>    BTRFS info (device dm-5): balance: start -d -m -s
>    BTRFS info (device dm-5): relocating block group 30408704 flags metadata|dup
>    BTRFS info (device dm-5): found 2 extents at MOVE_DATA_EXTENT stage
>    BTRFS info (device dm-5): relocating block group 22020096 flags system|dup
>    BTRFS info (device dm-5): found 1 extents at MOVE_DATA_EXTENT stage
>    BTRFS info (device dm-5): relocating block group 13631488 flags data
>    BTRFS info (device dm-5): found 1 extents at MOVE_DATA_EXTENT stage
>    BTRFS info (device dm-5): found 1 extents at UPDATE_DATA_PTRS stage
>    BTRFS info (device dm-5): balance: ended with status: 0
>
> The string "MOVE_DATA_EXTENT" and "UPDATE_DATA_PTRS" is mostly from the
> macro MOVE_DATA_EXTENTS and UPDATE_DATA_PTRS, but the 'S' from
> MOVE_DATA_EXTENTS is removed in the output string to make the alignment
> better.
>
> This patch will not increase the number of lines, but with extra info
> for us to debug the reported problem.
> (Although it's very likely the bug is sticking at UPDATE_DATA_PTRS
> stage, even without the patch)
>
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>   fs/btrfs/relocation.c | 16 ++++++++++++++--
>   1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
> index d897a8e5e430..88fd9182852d 100644
> --- a/fs/btrfs/relocation.c
> +++ b/fs/btrfs/relocation.c
> @@ -4291,6 +4291,15 @@ static void describe_relocation(struct btrfs_fs_info *fs_info,
>   		   block_group->start, buf);
>   }
>
> +static const char *stage_to_string(int stage)
> +{
> +	if (stage == MOVE_DATA_EXTENTS)
> +		return "MOVE_DATA_EXTENT";
> +	if (stage == UPDATE_DATA_PTRS)
> +		return "UPDATE_DATA_PTRS";
> +	return "UNKNOWN";
> +}
> +
>   /*
>    * function to relocate all extents in a block group.
>    */
> @@ -4365,12 +4374,15 @@ int btrfs_relocate_block_group(struct btrfs_fs_info *fs_info, u64 group_start)
>   				 rc->block_group->length);
>
>   	while (1) {
> +		int finishes_stage;
> +

NIT: the rc::stage is an unsigned integer.


>   		mutex_lock(&fs_info->cleaner_mutex);
>   		ret = relocate_block_group(rc);
>   		mutex_unlock(&fs_info->cleaner_mutex);
>   		if (ret < 0)
>   			err = ret;
>
> +		finishes_stage = rc->stage;
>   		/*
>   		 * We may have gotten ENOSPC after we already dirtied some
>   		 * extents.  If writeout happens while we're relocating a
> @@ -4396,8 +4408,8 @@ int btrfs_relocate_block_group(struct btrfs_fs_info *fs_info, u64 group_start)
>   		if (rc->extents_found == 0)
>   			break;
>
> -		btrfs_info(fs_info, "found %llu extents", rc->extents_found);
> -
> +		btrfs_info(fs_info, "found %llu extents at %s stage",
> +			   rc->extents_found, stage_to_string(finishes_stage));
>   	}
>
>   	WARN_ON(rc->block_group->pinned > 0);
>