Re: [PATCH v10 05/41] btrfs: check and enable ZONED mode

[Anand Jain <anand.jain@oracle.com>]

On 1/12/20 10:29 am, Damien Le Moal wrote:
> On 2020/12/01 11:20, Anand Jain wrote:
>> On 30/11/20 9:15 pm, Damien Le Moal wrote:
>>> On 2020/11/30 21:13, Anand Jain wrote:
>>>> On 28/11/20 2:44 am, David Sterba wrote:
>>>>> On Wed, Nov 18, 2020 at 07:29:20PM +0800, Anand Jain wrote:
>>>>>> On 10/11/20 7:26 pm, Naohiro Aota wrote:
>>>>>>> This commit introduces the function btrfs_check_zoned_mode() to check if
>>>>>>> ZONED flag is enabled on the file system and if the file system consists of
>>>>>>> zoned devices with equal zone size.
>>>>>>>
>>>>>>> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
>>>>>>> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
>>>>>>> Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
>>>>>>> Reviewed-by: Josef Bacik <josef@toxicpanda.com>
>>>>>>> ---
>>>>>>>      fs/btrfs/ctree.h       | 11 ++++++
>>>>>>>      fs/btrfs/dev-replace.c |  7 ++++
>>>>>>>      fs/btrfs/disk-io.c     | 11 ++++++
>>>>>>>      fs/btrfs/super.c       |  1 +
>>>>>>>      fs/btrfs/volumes.c     |  5 +++
>>>>>>>      fs/btrfs/zoned.c       | 81 ++++++++++++++++++++++++++++++++++++++++++
>>>>>>>      fs/btrfs/zoned.h       | 26 ++++++++++++++
>>>>>>>      7 files changed, 142 insertions(+)
>>>>>>>
>>>>>>> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
>>>>>>> index aac3d6f4e35b..453f41ca024e 100644
>>>>>>> --- a/fs/btrfs/ctree.h
>>>>>>> +++ b/fs/btrfs/ctree.h
>>>>>>> @@ -948,6 +948,12 @@ struct btrfs_fs_info {
>>>>>>>      	/* Type of exclusive operation running */
>>>>>>>      	unsigned long exclusive_operation;
>>>>>>>      
>>>>>>> +	/* Zone size when in ZONED mode */
>>>>>>> +	union {
>>>>>>> +		u64 zone_size;
>>>>>>> +		u64 zoned;
>>>>>>> +	};
>>>>>>> +
>>>>>>>      #ifdef CONFIG_BTRFS_FS_REF_VERIFY
>>>>>>>      	spinlock_t ref_verify_lock;
>>>>>>>      	struct rb_root block_tree;
>>>>>>> @@ -3595,4 +3601,9 @@ static inline int btrfs_is_testing(struct btrfs_fs_info *fs_info)
>>>>>>>      }
>>>>>>>      #endif
>>>>>>>      
>>>>>>> +static inline bool btrfs_is_zoned(struct btrfs_fs_info *fs_info)
>>>>>>> +{
>>>>>>> +	return fs_info->zoned != 0;
>>>>>>> +}
>>>>>>> +
>>>>>>>      #endif
>>>>>>> diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
>>>>>>> index 6f6d77224c2b..db87f1aa604b 100644
>>>>>>> --- a/fs/btrfs/dev-replace.c
>>>>>>> +++ b/fs/btrfs/dev-replace.c
>>>>>>> @@ -238,6 +238,13 @@ 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,
>>>>>>> +			  "dev-replace: zoned type of target device mismatch with filesystem");
>>>>>>> +		ret = -EINVAL;
>>>>>>> +		goto error;
>>>>>>> +	}
>>>>>>> +
>>>>>>>      	sync_blockdev(bdev);
>>>>>>>      
>>>>>>>      	list_for_each_entry(device, &fs_info->fs_devices->devices, dev_list) {
>>>>>>
>>>>>>      I am not sure if it is done in some other patch. But we still have to
>>>>>>      check for
>>>>>>
>>>>>>      (model == BLK_ZONED_HA && incompat_zoned))
>>>>>
>>>>> Do you really mean BLK_ZONED_HA, ie. host-aware (HA)?
>>>>> btrfs_check_device_zone_type checks for _HM.
>>>>
>>>>
>>>> Still confusing to me. The below function, which is part of this
>>>> patch, says we don't support BLK_ZONED_HM. So does it mean we
>>>> allow BLK_ZONED_HA only?
>>>>
>>>> +static inline bool btrfs_check_device_zone_type(struct btrfs_fs_info
>>>> *fs_info,
>>>> +						struct block_device *bdev)
>>>> +{
>>>> +	u64 zone_size;
>>>> +
>>>> +	if (btrfs_is_zoned(fs_info)) {
>>>> +		zone_size = (u64)bdev_zone_sectors(bdev) << SECTOR_SHIFT;
>>>> +		/* Do not allow non-zoned device */
>>>
>>> This comment does not make sense. It should be:
>>>
>>> 		/* Only allow zoned devices with the same zone size */
>>>
>>>> +		return bdev_is_zoned(bdev) && fs_info->zone_size == zone_size;
>>>> +	}
>>>> +
>>>> +	/* Do not allow Host Manged zoned device */
>>>> +	return bdev_zoned_model(bdev) != BLK_ZONED_HM;
>>>
>>> The comment is also wrong. It should read:
>>>
>>> 	/* Allow only host managed zoned devices */
>>>
>>> This is because we decided to treat host aware devices in the same way as
>>> regular block devices, since HA drives are backward compatible with regular
>>> block devices.
>>
>>
>> Yeah, I read about them, but I have questions like do an FS work on top
>> of a BLK_ZONED_HA without modification?
> 
> Yes. These drives are fully backward compatible and accept random writes
> anywhere. Performance however is potentially a different story as the drive will
> eventually need to do internal garbage collection of some sort, exactly like an
> SSD, but definitely not at SSD speeds :)
> 
>>    Are we ok to replace an HM device with a HA device? Or add a HA device
>> to a btrfs on an HM device.
> 
> We have a choice here: we can treat HA drives as regular devices or treat them
> as HM devices. Anything in between does not make sense. I am fine either way,
> the main reason being that there are no HA drive on the market today that I know
> of (this model did not have a lot of success due to the potentially very
> unpredictable performance depending on the use case).
> 
> So the simplest thing to do is, in my opinion, to ignore their "zone"
> characteristics and treat them as regular disks. But treating them as HM drives
> is a simple to do too.
> > Of note is that a host-aware drive will be reported by the block layer as
> BLK_ZONED_HA only as long as the drive does not have any partition. If it does,
> then the block layer will treat the drive as a regular disk.

IMO. For now, it is better to check for the BLK_ZONED_HA explicitly in a 
non-zoned-btrfs. And check for BLK_ZONED_HM explicitly in a zoned-btrfs. 
This way, if there is another type of BLK_ZONED_xx in the future, we 
have the opportunity to review to support it. As below [1]...

[1]
bool btrfs_check_device_type()
{
	if (bdev_is_zoned()) {
		if (btrfs_is_zoned())
			if (bdev_zoned_model == BLK_ZONED_HM)
			/* also check the zone_size. */
				return true;
		else
			if (bdev_zoned_model == BLK_ZONED_HA)
			/* a regular device and FS, no zone_size to check I think? */
				return true;
	} else {
		if (!btrfs_is_zoned())
			return true
	}

	return false;
}

Thanks.

> 
>>
>> Thanks.
>>
>>>
>>>> +}
>>>>
>>>>
>>>> Also, if there is a new type of zoned device in the future, the older
>>>> kernel should be able to reject the newer zone device types.
>>>>
>>>> And, if possible could you rename above function to
>>>> btrfs_zone_type_is_valid(). Or better.
>>>>
>>>>
>>>>>> right? What if in a non-zoned FS, a zoned device is added through the
>>>>>> replace. No?
>>>>>
>>>>> The types of devices cannot mix, yeah. So I'd like to know the answer as
>>>>> well.
>>>>
>>>>
>>>>>>> --- a/fs/btrfs/volumes.c
>>>>>>> +++ b/fs/btrfs/volumes.c
>>>>>>> @@ -2518,6 +2518,11 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
>>>>>>>      	if (IS_ERR(bdev))
>>>>>>>      		return PTR_ERR(bdev);
>>>>>>>      
>>>>>>> +	if (!btrfs_check_device_zone_type(fs_info, bdev)) {
>>>>>>> +		ret = -EINVAL;
>>>>>>> +		goto error;
>>>>>>> +	}
>>>>>>> +
>>>>>>>      	if (fs_devices->seeding) {
>>>>>>>      		seeding_dev = 1;
>>>>>>>      		down_write(&sb->s_umount);
>>>>>>
>>>>>> Same here too. It can also happen that a zone device is added to a non
>>>>>> zoned fs.
>>>>
>>>>
>>>> Thanks.