Re: [PATCH] btrfs: dump extra info if one free space cache has more bitmaps than it should

[Anand Jain <anand.jain@oracle.com>]

On 01/08/2022 09:35, Qu Wenruo wrote:
> There is an internal report on hitting the following ASSERT() in
> recalculate_thresholds():
> 
>   	ASSERT(ctl->total_bitmaps <= max_bitmaps);
> 
> Above @max_bitmaps is calculated using the following variables:
> 
> - bytes_per_bg
>    8 * 4096 * 4096 (128M) for x86_64/x86.
> 
> - block_group->length
>    The length of the block group.
> 
> @max_bitmaps is the rounded up value of block_group->length / 128M.
> 
> Normally one free space cache should not have more bitmaps than above
> value, but when it happens the ASSERT() can be triggered if
> CONFIG_BTRFS_ASSERT is also enabled.
> 
> But the ASSERT() itself won't provide enough info to know which is going
> wrong.
> Is the bg too small thus it only allows one bitmap?
> Or is there something else wrong?
> 
> So although I haven't found extra reports or crash dump to do further
> investigation, add the extra info to make it more helpful to debug.
> 
  I guess there is no reproducer. If there is any other related may be 
added such as configs etc.

> Signed-off-by: Qu Wenruo <wqu@suse.com>

Reviewed-by: Anand Jain <anand.jain@oracle.com>


> ---
>   fs/btrfs/free-space-cache.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
> index 996da650ecdc..4ebfd9b7bc53 100644
> --- a/fs/btrfs/free-space-cache.c
> +++ b/fs/btrfs/free-space-cache.c
> @@ -693,6 +693,12 @@ static void recalculate_thresholds(struct btrfs_free_space_ctl *ctl)
>   
>   	max_bitmaps = max_t(u64, max_bitmaps, 1);
>   
> +	if (ctl->total_bitmaps > max_bitmaps)
> +		btrfs_err(block_group->fs_info,
> +	"invalid free space control: bg start=%llu len=%llu total_bitmaps=%u unit=%u max_bitmaps=%llu bytes_per_bg=%llu",
> +			  block_group->start, block_group->length,
> +			  ctl->total_bitmaps, ctl->unit, max_bitmaps,
> +			  bytes_per_bg);
>   	ASSERT(ctl->total_bitmaps <= max_bitmaps);
>   
>   	/*