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

[Damien Le Moal <Damien.LeMoal@wdc.com>]

On 2020/06/26 14:58, Javier González wrote:
> 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?

But REQ_OP_ZONE_RESET_ALL is already implemented and supported and will reset
all zones of a drive using a single command if the ioctl is called for the
entire sector range of a physical drive. For device mapper with a partial
mapping, the per zone reset loop will be used. If you have no other use case for
the REQ_ZONE_ALL flag, what is the point here ? Reset is already optimized for
the all zones case

> 
> Javier
> 


-- 
Damien Le Moal
Western Digital Research