Re: [PATCH 2/6] block: add support for selecting all zones

["Javier González" <javier@javigon.com>]

On 26.06.2020 01:27, Damien Le Moal wrote:
>On 2020/06/25 21:22, Javier González wrote:
>> From: Javier González <javier.gonz@samsung.com>
>>
>> Add flag to allow selecting all zones on a single zone management
>> operation
>>
>> Signed-off-by: Javier González <javier.gonz@samsung.com>
>> Signed-off-by: SelvaKumar S <selvakuma.s1@samsung.com>
>> Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
>> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
>> ---
>>  block/blk-zoned.c             | 3 +++
>>  include/linux/blk_types.h     | 3 ++-
>>  include/uapi/linux/blkzoned.h | 9 +++++++++
>>  3 files changed, 14 insertions(+), 1 deletion(-)
>>
>> diff --git a/block/blk-zoned.c b/block/blk-zoned.c
>> index e87c60004dc5..29194388a1bb 100644
>> --- a/block/blk-zoned.c
>> +++ b/block/blk-zoned.c
>> @@ -420,6 +420,9 @@ int blkdev_zone_mgmt_ioctl(struct block_device *bdev, fmode_t mode,
>>  		return -ENOTTY;
>>  	}
>>
>> +	if (zmgmt.flags & BLK_ZONE_SELECT_ALL)
>> +		op |= REQ_ZONE_ALL;
>> +
>>  	return blkdev_zone_mgmt(bdev, op, zmgmt.sector, zmgmt.nr_sectors,
>>  				GFP_KERNEL);
>>  }
>> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
>> index ccb895f911b1..16b57fb2b99c 100644
>> --- a/include/linux/blk_types.h
>> +++ b/include/linux/blk_types.h
>> @@ -351,6 +351,7 @@ enum req_flag_bits {
>>  	 * work item to avoid such priority inversions.
>>  	 */
>>  	__REQ_CGROUP_PUNT,
>> +	__REQ_ZONE_ALL,		/* apply zone operation to all zones */
>>
>>  	/* command specific flags for REQ_OP_WRITE_ZEROES: */
>>  	__REQ_NOUNMAP,		/* do not free blocks when zeroing */
>> @@ -378,7 +379,7 @@ enum req_flag_bits {
>>  #define REQ_BACKGROUND		(1ULL << __REQ_BACKGROUND)
>>  #define REQ_NOWAIT		(1ULL << __REQ_NOWAIT)
>>  #define REQ_CGROUP_PUNT		(1ULL << __REQ_CGROUP_PUNT)
>> -
>> +#define REQ_ZONE_ALL		(1ULL << __REQ_ZONE_ALL)
>>  #define REQ_NOUNMAP		(1ULL << __REQ_NOUNMAP)
>>  #define REQ_HIPRI		(1ULL << __REQ_HIPRI)
>>
>> diff --git a/include/uapi/linux/blkzoned.h b/include/uapi/linux/blkzoned.h
>> index 07b5fde21d9f..a8c89fe58f97 100644
>> --- a/include/uapi/linux/blkzoned.h
>> +++ b/include/uapi/linux/blkzoned.h
>> @@ -157,6 +157,15 @@ enum blk_zone_action {
>>  	BLK_ZONE_MGMT_RESET	= 0x4,
>>  };
>>
>> +/**
>> + * enum blk_zone_mgmt_flags - Flags for blk_zone_mgmt
>> + *
>> + * BLK_ZONE_SELECT_ALL: Select all zones for current zone action
>> + */
>> +enum blk_zone_mgmt_flags {
>> +	BLK_ZONE_SELECT_ALL	= 1 << 0,
>> +};
>> +
>>  /**
>>   * struct blk_zone_mgmt - Extended zoned management
>>   *
>>
>
>NACK.
>
>Details:
>1) REQ_OP_ZONE_RESET together with REQ_ZONE_ALL is the same as
>REQ_OP_ZONE_RESET_ALL, isn't it ? You are duplicating a functionality that
>already exists.
>2) The patch introduces REQ_ZONE_ALL at the block layer only without defining
>how it ties into SCSI and NVMe driver use of it. Is REQ_ZONE_ALL indicating that
>the zone management commands are to be executed with the ALL bit set ? If yes,
>that will break device-mapper. See the special code for handling
>REQ_OP_ZONE_RESET_ALL. That code is in place for a reason: the target block
>device may not be an entire physical device. In that case, applying a zone
>management command to all zones of the physical drive is wrong.
>3) REQ_ZONE_ALL seems completely equivalent to specifying a sector range of [0
>.. drive capacity]. So what is the point ? The current interface handles that.
>That is how we chose between REQ_OP_ZONE_RESET and REQ_OP_ZONE_RESET_ALL right now.
>4) Without any in-kernel user, I do not see the point. And for applications, I
>do not see any good use case for doing open all, close all, offline all or
>finish all. If you have any such good use case, please elaborate.
>

The main use if reset all, but without having to look through all zones,
as it imposes an overhead when we have a large number of zones. Having
the possibility to offload it to HW is more efficient.

I had not thought about the device mapper use case. Would it be an
option to translate this into REQ_OP_ZONE_RESET_ALL when we have a
device mapper (or any other case where this might break) and then leave
the bit go to the driver if it applies to the whole device?

Javier