Re: [PATCH 09/19] btrfs: limit super block locations in HMZONED mode

[Anand Jain]

On 7/6/19 9:10 PM, Naohiro Aota wrote:
> When in HMZONED mode, make sure that device super blocks are located in
> randomly writable zones of zoned block devices. That is, do not write super
> blocks in sequential write required zones of host-managed zoned block
> devices as update would not be possible.

 By design all copies of SB must be updated at each transaction,
 as they are redundant copies they must match at the end of
 each transaction.

 Instead of skipping the sb updates, why not alter number of
 copies at the time of mkfs.btrfs?

Thanks, Anand


> Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx>
> Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
> ---
>   fs/btrfs/disk-io.c     | 11 +++++++++++
>   fs/btrfs/disk-io.h     |  1 +
>   fs/btrfs/extent-tree.c |  4 ++++
>   fs/btrfs/scrub.c       |  2 ++
>   4 files changed, 18 insertions(+)
>
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index 7c1404c76768..ddbb02906042 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -3466,6 +3466,13 @@ struct buffer_head *btrfs_read_dev_super(struct block_device *bdev)
>   	return latest;
>   }
>   
> +int btrfs_check_super_location(struct btrfs_device *device, u64 pos)
> +{
> +	/* any address is good on a regular (zone_size == 0) device */
> +	/* non-SEQUENTIAL WRITE REQUIRED zones are capable on a zoned device */
> +	return device->zone_size == 0 || !btrfs_dev_is_sequential(device, pos);
> +}
> +
>   /*
>    * Write superblock @sb to the @device. Do not wait for completion, all the
>    * buffer heads we write are pinned.
> @@ -3495,6 +3502,8 @@ static int write_dev_supers(struct btrfs_device *device,
>   		if (bytenr + BTRFS_SUPER_INFO_SIZE >=
>   		    device->commit_total_bytes)
>   			break;
> +		if (!btrfs_check_super_location(device, bytenr))
> +			continue;
>   
>   		btrfs_set_super_bytenr(sb, bytenr);
>   
> @@ -3561,6 +3570,8 @@ static int wait_dev_supers(struct btrfs_device *device, int max_mirrors)
>   		if (bytenr + BTRFS_SUPER_INFO_SIZE >=
>   		    device->commit_total_bytes)
>   			break;
> +		if (!btrfs_check_super_location(device, bytenr))
> +			continue;
>   
>   		bh = __find_get_block(device->bdev,
>   				      bytenr / BTRFS_BDEV_BLOCKSIZE,
> diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
> index a0161aa1ea0b..70e97cd6fa76 100644
> --- a/fs/btrfs/disk-io.h
> +++ b/fs/btrfs/disk-io.h
> @@ -141,6 +141,7 @@ struct extent_map *btree_get_extent(struct btrfs_inode *inode,
>   		struct page *page, size_t pg_offset, u64 start, u64 len,
>   		int create);
>   int btrfs_get_num_tolerated_disk_barrier_failures(u64 flags);
> +int btrfs_check_super_location(struct btrfs_device *device, u64 pos);
>   int __init btrfs_end_io_wq_init(void);
>   void __cold btrfs_end_io_wq_exit(void);
>   
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 3d41d840fe5c..ae2c895d08c4 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -267,6 +267,10 @@ static int exclude_super_stripes(struct btrfs_block_group_cache *cache)
>   			return ret;
>   	}
>   
> +	/* we won't have super stripes in sequential zones */
> +	if (cache->alloc_type == BTRFS_ALLOC_SEQ)
> +		return 0;
> +
>   	for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
>   		bytenr = btrfs_sb_offset(i);
>   		ret = btrfs_rmap_block(fs_info, cache->key.objectid,
> diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
> index f7b29f9db5e2..36ad4fad7eaf 100644
> --- a/fs/btrfs/scrub.c
> +++ b/fs/btrfs/scrub.c
> @@ -3720,6 +3720,8 @@ static noinline_for_stack int scrub_supers(struct scrub_ctx *sctx,
>   		if (bytenr + BTRFS_SUPER_INFO_SIZE >
>   		    scrub_dev->commit_total_bytes)
>   			break;
> +		if (!btrfs_check_super_location(scrub_dev, bytenr))
> +			continue;
>   
>   		ret = scrub_pages(sctx, bytenr, BTRFS_SUPER_INFO_SIZE, bytenr,
>   				  scrub_dev, BTRFS_EXTENT_FLAG_SUPER, gen, i,