Re: [PATCH v2] btrfs: Add chunk allocation ENOSPC debug message for enospc_debug mount option

[Nikolay Borisov <nborisov@suse.com>]

On 22.01.2018 07:50, Qu Wenruo wrote:
> Enospc_debug makes extent allocator to print more debug messages,
> however for chunk allocation, there is no debug message for enospc_debug
> at all.
> 
> This patch will add message for the following parts of chunk allocator:
> 
> 1) No rw device at all
>    Quite rare, but at least output one message for this case.
> 
> 2) No enough space for some device
>    This debug message is quite handy for unbalanced disks with stripe
>    based profiles (RAID0/10/5/6).
> 
> 3) Not enough free devices
>    This debug message should tell us if current chunk allocator is
>    working correctly on minimal device requirement.
> 
> Although under most case, we will hit other ENOSPC before we even hit a
> chunk allocator ENOSPC, but such debug info won't help.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Reviewed-by: Nikolay Borisov <nborisov@suse.com>

> ---
> v2:
>   Unify all message level to btrfs_debug().
>   More meaningful message if we don't have enough device.
> ---
>  fs/btrfs/volumes.c | 19 +++++++++++++++++--
>  1 file changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index a25684287501..86cae6a15b1e 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -4622,8 +4622,11 @@ static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
>  
>  	BUG_ON(!alloc_profile_is_valid(type, 0));
>  
> -	if (list_empty(&fs_devices->alloc_list))
> +	if (list_empty(&fs_devices->alloc_list)) {
> +		if (btrfs_test_opt(info, ENOSPC_DEBUG))
> +			btrfs_debug(info, "%s: No writable device", __func__);
>  		return -ENOSPC;
> +	}
>  
>  	index = __get_raid_index(type);
>  
> @@ -4705,8 +4708,14 @@ static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
>  		if (ret == 0)
>  			max_avail = max_stripe_size * dev_stripes;
>  
> -		if (max_avail < BTRFS_STRIPE_LEN * dev_stripes)
> +		if (max_avail < BTRFS_STRIPE_LEN * dev_stripes) {
> +			if (btrfs_test_opt(info, ENOSPC_DEBUG))
> +				btrfs_debug(info,
> +			"%s: devid %llu has no free space, have=%llu want=%u",
> +					    __func__, device->devid, max_avail,
> +					    BTRFS_STRIPE_LEN * dev_stripes);
>  			continue;
> +		}
>  
>  		if (ndevs == fs_devices->rw_devices) {
>  			WARN(1, "%s: found more than %llu devices\n",
> @@ -4731,6 +4740,12 @@ static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
>  
>  	if (ndevs < devs_increment * sub_stripes || ndevs < devs_min) {
>  		ret = -ENOSPC;
> +		if (btrfs_test_opt(info, ENOSPC_DEBUG)) {
> +			btrfs_debug(info,
> +		"%s: not enough devices with free space: have=%d minimal required=%d",

nit: s/minimal/minimum
But there is no point in resending just for that, I guess David could
fix it while merging.

> +				    __func__, ndevs, min(devs_min,
> +				    devs_increment * sub_stripes));
> +		}
>  		goto error;
>  	}
>  
>