Re: [PATCH v4 03/27] btrfs: Check and enable HMZONED mode

[Johannes Thumshirn <jthumshirn@suse.de>]

On 23/08/2019 12:10, Naohiro Aota wrote:
> HMZONED mode cannot be used together with the RAID5/6 profile for now.
> Introduce the function btrfs_check_hmzoned_mode() to check this. This
> function will also check if HMZONED flag is enabled on the file system and
> if the file system consists of zoned devices with equal zone size.
> 
> Additionally, as updates to the space cache are in-place, the space cache
> cannot be located over sequential zones and there is no guarantees that the
> device will have enough conventional zones to store this cache. Resolve
> this problem by disabling completely the space cache.  This does not
completely disabling ~^

> introduces any problems with sequential block groups: all the free space is
introduce ~^

> located after the allocation pointer and no free space before the pointer.
                                           is located? ~^
> There is no need to have such cache.
> 
> For the same reason, NODATACOW is also disabled.
> 
> Also INODE_MAP_CACHE is also disabled to avoid preallocation in the
> INODE_MAP_CACHE inode.
> 
> In summary, HMZONED will disable:
> 
> | Disabled features | Reason                                              |
> |-------------------+-----------------------------------------------------|
> | RAID5/6           | 1) Non-full stripe write cause overwriting of       |
> |                   | parity block                                        |
> |                   | 2) Rebuilding on high capacity volume (usually with |
> |                   | SMR) can lead to higher failure rate                |
> |-------------------+-----------------------------------------------------|
> | space_cache (v1)  | In-place updating                                   |
> | NODATACOW         | In-place updating                                   |
> |-------------------+-----------------------------------------------------|
> | tree-log          | Partial write out of metadata creates write holes   |
> |-------------------+-----------------------------------------------------|
> | fallocate         | Reserved extent will be a write hole                |
> | INODE_MAP_CACHE   | Need pre-allocation. (and will be deprecated?)      |
> |-------------------+-----------------------------------------------------|
> | MIXED_BG          | Allocated metadata region will be write holes for   |
> |                   | data writes                                         |
> | async checksum    | Not to mix up bios by multiple workers              |
> 
> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
> Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
> ---
>  fs/btrfs/ctree.h       |  3 ++
>  fs/btrfs/dev-replace.c |  8 +++++
>  fs/btrfs/disk-io.c     |  8 +++++
>  fs/btrfs/hmzoned.c     | 67 ++++++++++++++++++++++++++++++++++++++++++
>  fs/btrfs/hmzoned.h     | 18 ++++++++++++
>  fs/btrfs/super.c       |  1 +
>  fs/btrfs/volumes.c     |  5 ++++
>  7 files changed, 110 insertions(+)
> 
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 94660063a162..221259737703 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -712,6 +712,9 @@ struct btrfs_fs_info {
>  	struct btrfs_root *uuid_root;
>  	struct btrfs_root *free_space_root;
>  
> +	/* Zone size when in HMZONED mode */
> +	u64 zone_size;
> +
>  	/* the log root tree is a directory of all the other log roots */
>  	struct btrfs_root *log_root_tree;
>  
> diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
> index 6b2e9aa83ffa..2cc3ac4d101d 100644
> --- a/fs/btrfs/dev-replace.c
> +++ b/fs/btrfs/dev-replace.c
> @@ -20,6 +20,7 @@
>  #include "rcu-string.h"
>  #include "dev-replace.h"
>  #include "sysfs.h"
> +#include "hmzoned.h"
>  
>  static int btrfs_dev_replace_finishing(struct btrfs_fs_info *fs_info,
>  				       int scrub_ret);
> @@ -201,6 +202,13 @@ static int btrfs_init_dev_replace_tgtdev(struct btrfs_fs_info *fs_info,
>  		return PTR_ERR(bdev);
>  	}
>  
> +	if (!btrfs_check_device_zone_type(fs_info, bdev)) {
> +		btrfs_err(fs_info,
> +			  "zone type of target device mismatch with the filesystem!");
> +		ret = -EINVAL;
> +		goto error;
> +	}
> +
>  	sync_blockdev(bdev);
>  
>  	devices = &fs_info->fs_devices->devices;
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index 97beb351a10c..3f5ea92f546c 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -40,6 +40,7 @@
>  #include "compression.h"
>  #include "tree-checker.h"
>  #include "ref-verify.h"
> +#include "hmzoned.h"
>  
>  #define BTRFS_SUPER_FLAG_SUPP	(BTRFS_HEADER_FLAG_WRITTEN |\
>  				 BTRFS_HEADER_FLAG_RELOC |\
> @@ -3121,6 +3122,13 @@ int open_ctree(struct super_block *sb,
>  
>  	btrfs_free_extra_devids(fs_devices, 1);
>  
> +	ret = btrfs_check_hmzoned_mode(fs_info);
> +	if (ret) {
> +		btrfs_err(fs_info, "failed to init hmzoned mode: %d",
> +				ret);
> +		goto fail_block_groups;
> +	}
> +
>  	ret = btrfs_sysfs_add_fsid(fs_devices, NULL);
>  	if (ret) {
>  		btrfs_err(fs_info, "failed to init sysfs fsid interface: %d",
> diff --git a/fs/btrfs/hmzoned.c b/fs/btrfs/hmzoned.c
> index 23bf58d3d7bb..ca58eee08a70 100644
> --- a/fs/btrfs/hmzoned.c
> +++ b/fs/btrfs/hmzoned.c
> @@ -157,3 +157,70 @@ int btrfs_get_dev_zone(struct btrfs_device *device, u64 pos,
>  
>  	return 0;
>  }
> +
> +int btrfs_check_hmzoned_mode(struct btrfs_fs_info *fs_info)
> +{
> +	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
> +	struct btrfs_device *device;
> +	u64 hmzoned_devices = 0;
> +	u64 nr_devices = 0;
> +	u64 zone_size = 0;
> +	int incompat_hmzoned = btrfs_fs_incompat(fs_info, HMZONED);
> +	int ret = 0;
> +
> +	/* Count zoned devices */
> +	list_for_each_entry(device, &fs_devices->devices, dev_list) {
> +		if (!device->bdev)
> +			continue;
> +		if (bdev_zoned_model(device->bdev) == BLK_ZONED_HM ||
> +		    (bdev_zoned_model(device->bdev) == BLK_ZONED_HA &&
> +		     incompat_hmzoned)) {
> +			hmzoned_devices++;
> +			if (!zone_size) {
> +				zone_size = device->zone_info->zone_size;
> +			} else if (device->zone_info->zone_size != zone_size) {
> +				btrfs_err(fs_info,
> +					  "Zoned block devices must have equal zone sizes");
> +				ret = -EINVAL;
> +				goto out;
> +			}
> +		}
> +		nr_devices++;
> +	}
> +
> +	if (!hmzoned_devices && incompat_hmzoned) {
> +		/* No zoned block device found on HMZONED FS */
> +		btrfs_err(fs_info, "HMZONED enabled file system should have zoned devices");
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	if (!hmzoned_devices && !incompat_hmzoned)
> +		goto out;
> +
> +	fs_info->zone_size = zone_size;
> +
> +	if (hmzoned_devices != nr_devices) {
> +		btrfs_err(fs_info,
> +			  "zoned devices cannot be mixed with regular devices");
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	/*
> +	 * stripe_size is always aligned to BTRFS_STRIPE_LEN in
> +	 * __btrfs_alloc_chunk(). Since we want stripe_len == zone_size,
> +	 * check the alignment here.
> +	 */
> +	if (!IS_ALIGNED(zone_size, BTRFS_STRIPE_LEN)) {
> +		btrfs_err(fs_info,
> +			  "zone size is not aligned to BTRFS_STRIPE_LEN");
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	btrfs_info(fs_info, "HMZONED mode enabled, zone size %llu B",
> +		   fs_info->zone_size);
> +out:
> +	return ret;
> +}
> diff --git a/fs/btrfs/hmzoned.h b/fs/btrfs/hmzoned.h
> index ffc70842135e..29cfdcabff2f 100644
> --- a/fs/btrfs/hmzoned.h
> +++ b/fs/btrfs/hmzoned.h
> @@ -9,6 +9,8 @@
>  #ifndef BTRFS_HMZONED_H
>  #define BTRFS_HMZONED_H
>  
> +#include <linux/blkdev.h>
> +
>  struct btrfs_zoned_device_info {
>  	/*
>  	 * Number of zones, zone size and types of zones if bdev is a
> @@ -25,6 +27,7 @@ int btrfs_get_dev_zone(struct btrfs_device *device, u64 pos,
>  		       struct blk_zone *zone, gfp_t gfp_mask);
>  int btrfs_get_dev_zone_info(struct btrfs_device *device);
>  void btrfs_destroy_dev_zone_info(struct btrfs_device *device);
> +int btrfs_check_hmzoned_mode(struct btrfs_fs_info *fs_info);


While we're at it, shouldn't all the functions in hmzoned.[ch] have a
!CONFIG_BLK_DEV_ZONED compat wrapper and hmzoned.o is dependent on
CONFIG_BLK_DEV_ZONED?

-- 
Johannes Thumshirn                            SUSE Labs Filesystems
jthumshirn@suse.de                                +49 911 74053 689
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