Re: [PATCH 7/9] btrfs: make btrfs_submit_compressed_read() to determine stripe boundary at bio allocation time

From: Johannes Thumshirn <Johannes.Thumshirn@wdc.com>
To: Qu Wenruo <wqu@suse.com>,
	"linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>
Subject: Re: [PATCH 7/9] btrfs: make btrfs_submit_compressed_read() to determine stripe boundary at bio allocation time
Date: Fri, 11 Jun 2021 07:42:50 +0000	[thread overview]
Message-ID: <PH0PR04MB7416B38BCA52ADBB748E31109B349@PH0PR04MB7416.namprd04.prod.outlook.com> (raw)
In-Reply-To: 20210611013114.57264-8-wqu@suse.com

On 11/06/2021 03:32, Qu Wenruo wrote:
> @@ -443,7 +449,6 @@ static struct bio *alloc_compressed_bio(struct compressed_bio *cb, u64 disk_byte
>  	bio->bi_end_io = endio_func;
>  
>  	if (bio_op(bio) == REQ_OP_ZONE_APPEND) {
> -		struct btrfs_fs_info *fs_info = btrfs_sb(cb->inode->i_sb);
>  		struct btrfs_device *device;
>  
>  		device = btrfs_zoned_get_device(fs_info, disk_bytenr,
> @@ -454,6 +459,15 @@ static struct bio *alloc_compressed_bio(struct compressed_bio *cb, u64 disk_byte
>  		}
>  		bio_set_dev(bio, device->bdev);
>  	}
> +	em = btrfs_get_chunk_map(fs_info, disk_bytenr, fs_info->sectorsize);
> +	if (IS_ERR(em))
> +		return ERR_CAST(em);
> +	ret = btrfs_get_io_geometry(fs_info, em, btrfs_op(bio), disk_bytenr,
> +				    &geom);
> +	free_extent_map(em);
> +	if (ret < 0)
> +		return ERR_PTR(ret);
> +	*next_stripe_start = disk_bytenr + geom.len;
>  	return bio;
>  }
>  

If you're doing a chunk map lookup on allocation you can kill above btrfs_zoned_get_device()
call and grab the block device for bio_set_dev() directly from the 1st stripe. Otherwise we're
doing two chunk map lookups for zoned btrfs after another, which is inefficient.