Re: [PATCH 10/11] btrfs: make the btrfs_io_context allocation in __btrfs_map_block optional

[Nikolay Borisov <nborisov@suse.com>]

On 13.07.22 г. 12:58 ч., Johannes Thumshirn wrote:
> On 13.07.22 08:14, Christoph Hellwig wrote:
>> +	/*
>> +	 * If this I/O maps to a single device, try to return the device and
>> +	 * physical block information on the stack instead of allocating an
>> +	 * I/O context structure.
>> +	 */
>> +	if (smap && num_alloc_stripes == 1 &&
>> +	    !((map->type & BTRFS_BLOCK_GROUP_RAID56_MASK) && mirror_num > 1) &&
>> +	    (!need_full_stripe(op) || !dev_replace_is_ongoing ||
>> +	     !dev_replace->tgtdev)) {
>> +		if (unlikely(patch_the_first_stripe_for_dev_replace)) {
>> +			smap->dev = dev_replace->tgtdev;
>> +			smap->physical = physical_to_patch_in_first_stripe;
>> +			*mirror_num_p = map->num_stripes + 1;
>> +		} else {
>> +			set_stripe(smap, map, stripe_index, stripe_offset,
>> +				   stripe_nr);
>> +			*mirror_num_p = mirror_num;
>> +		}
>> +		*bioc_ret = NULL;
>> +		ret = 0;
>> +		goto out;
>> +	}
>> +
> 
> 
> Could be my changes on top, but in order to get RAID0 with a raid-stripe-tree
> working I needed the following change:
> 
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index a7886e421153..344d2cf941a7 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -6506,7 +6506,7 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
>           * physical block information on the stack instead of allocating an
>           * I/O context structure.
>           */
> -       if (smap && num_alloc_stripes == 1 &&
> +       if (smap && num_alloc_stripes == 1 && !(map->type & BTRFS_BLOCK_GROUP_STRIPE_MASK) &&

nit: BLOCK_GROUP_STRIPE_MASK already contains BLOCK_GROUP_RAID56_MASK so 
BTRFS_BLOCK_GROUP_RAID56_MASK can be replaced. But I agree with hch that 
this change should come with your series.

>              !((map->type & BTRFS_BLOCK_GROUP_RAID56_MASK) && mirror_num > 1) &&
>              (!need_full_stripe(op) || !dev_replace_is_ongoing ||
>               !dev_replace->tgtdev)) {
>