On 2020/12/01 14:54, Anand Jain wrote:
> 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@xxxxxxx>
>>>>>>>> Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx>
>>>>>>>> Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
>>>>>>>> Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
>>>>>>>> ---
>>>>>>>> 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.
Sure, we can. But since HA drives are backward compatible, not sure the HA check
for non-zoned make sense. As long as the zoned flag is not set, the drive can be
used like a regular disk. If the user really want to use it as a zoned drive,
then it can format with force selecting the zoned flag in btrfs super. Then the
HA drive will be used as a zoned disk, exactly like HM disks.
> 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]...
It is very unlikely that we will see any other zone model. ZNS adopted the HM
model in purpose, to avoid multiplying the possible models, making the ecosystem
effort a nightmare.
>
> [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.
Works for me. May be reverse the conditions to make things easier to read and
understand:
bool btrfs_check_device_type()
{
if (btrfs_is_zoned()) {
if (bdev_is_zoned()) {
/* also check the zone_size. */
return true;
}
/*
* Regular device: emulate zones with zone size equal
* to device extent size.
*/
return true;
}
if (bdev_zoned_model == BLK_ZONED_HM) {
/* Zoned HM device require zoned btrfs */
return false;
}
/* Regular device or zoned HA device used as a regular device */
return true;
}
--
Damien Le Moal
Western Digital Research
