Re: [PATCH 02/19] btrfs: Get zone information of zoned block devices

[Naohiro Aota]

On 2019/06/18 3:56, David Sterba wrote:
> On Fri, Jun 07, 2019 at 10:10:08PM +0900, Naohiro Aota wrote:
>> If a zoned block device is found, get its zone information (number of zones
>> and zone size) using the new helper function btrfs_get_dev_zonetypes().  To
>> avoid costly run-time zone report commands to test the device zones type
>> during block allocation, attach the seqzones bitmap to the device structure
>> to indicate if a zone is sequential or accept random writes.
>>
>> This patch also introduces the helper function btrfs_dev_is_sequential() to
>> test if the zone storing a block is a sequential write required zone.
>>
>> Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx>
>> Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
>> ---
>>   fs/btrfs/volumes.c | 143 +++++++++++++++++++++++++++++++++++++++++++++
>>   fs/btrfs/volumes.h |  33 +++++++++++
>>   2 files changed, 176 insertions(+)
>>
>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
>> index 1c2a6e4b39da..b673178718e3 100644
>> --- a/fs/btrfs/volumes.c
>> +++ b/fs/btrfs/volumes.c
>> @@ -786,6 +786,135 @@ static int btrfs_free_stale_devices(const char *path,
>>   	return ret;
>>   }
>>   
>> +static int __btrfs_get_dev_zones(struct btrfs_device *device, u64 pos,
> 
> Please drop __ from the name, the pattern where this naming makes sense
> does not apply here. It's for cases where teh function wihout
> underscores does some extra stuff like locking and the underscored does
> not and this is used on some context. I haven't found
> btrfs_get_dev_zones in this or other patches.
> 
>> +				 struct blk_zone **zones,
>> +				 unsigned int *nr_zones, gfp_t gfp_mask)
>> +{
>> +	struct blk_zone *z = *zones;
> 
> This may apply to more places, plese don't use single letter for
> anything else than 'i' and similar. 'zone' would be suitable.

Sure.

>> +	int ret;
>> +
>> +	if (!z) {
>> +		z = kcalloc(*nr_zones, sizeof(struct blk_zone), GFP_KERNEL);
>> +		if (!z)
>> +			return -ENOMEM;
>> +	}
>> +
>> +	ret = blkdev_report_zones(device->bdev, pos >> SECTOR_SHIFT,
>> +				  z, nr_zones, gfp_mask);
>> +	if (ret != 0) {
>> +		btrfs_err(device->fs_info, "Get zone at %llu failed %d\n",
> 
> No capital letter and no "\n" at the end of the message, that's added by
> btrfs_er.

oops, I overlooked it...

>> +			  pos, ret);
>> +		return ret;
>> +	}
>> +
>> +	*zones = z;
>> +
>> +	return 0;
>> +}
>> +
>> +static void btrfs_destroy_dev_zonetypes(struct btrfs_device *device)
>> +{
>> +	kfree(device->seq_zones);
>> +	kfree(device->empty_zones);
>> +	device->seq_zones = NULL;
>> +	device->empty_zones = NULL;
>> +	device->nr_zones = 0;
>> +	device->zone_size = 0;
>> +	device->zone_size_shift = 0;
>> +}
>> +
>> +int btrfs_get_dev_zone(struct btrfs_device *device, u64 pos,
>> +		       struct blk_zone *zone, gfp_t gfp_mask)
>> +{
>> +	unsigned int nr_zones = 1;
>> +	int ret;
>> +
>> +	ret = __btrfs_get_dev_zones(device, pos, &zone, &nr_zones, gfp_mask);
>> +	if (ret != 0 || !nr_zones)
>> +		return ret ? ret : -EIO;
>> +
>> +	return 0;
>> +}
>> +
>> +int btrfs_get_dev_zonetypes(struct btrfs_device *device)
>> +{
>> +	struct block_device *bdev = device->bdev;
>> +	sector_t nr_sectors = bdev->bd_part->nr_sects;
>> +	sector_t sector = 0;
>> +	struct blk_zone *zones = NULL;
>> +	unsigned int i, n = 0, nr_zones;
>> +	int ret;
>> +
>> +	device->zone_size = 0;
>> +	device->zone_size_shift = 0;
>> +	device->nr_zones = 0;
>> +	device->seq_zones = NULL;
>> +	device->empty_zones = NULL;
>> +
>> +	if (!bdev_is_zoned(bdev))
>> +		return 0;
>> +
>> +	device->zone_size = (u64)bdev_zone_sectors(bdev) << SECTOR_SHIFT;
>> +	device->zone_size_shift = ilog2(device->zone_size);
>> +	device->nr_zones = nr_sectors >> ilog2(bdev_zone_sectors(bdev));
>> +	if (nr_sectors & (bdev_zone_sectors(bdev) - 1))
>> +		device->nr_zones++;
>> +
>> +	device->seq_zones = kcalloc(BITS_TO_LONGS(device->nr_zones),
>> +				    sizeof(*device->seq_zones), GFP_KERNEL);
> 
> What's the expected range for the allocation size? There's one bit per
> zone, so one 4KiB page can hold up to 32768 zones, with 1GiB it's 32TiB
> of space on the drive. Ok that seems safe for now.

Typically, zone size is 256MB (as default value in tcmu-runner). On such device,
we need one 4KB page per 8TB disk space. Still it's quite safe.

>> +	if (!device->seq_zones)
>> +		return -ENOMEM;
>> +
>> +	device->empty_zones = kcalloc(BITS_TO_LONGS(device->nr_zones),
>> +				      sizeof(*device->empty_zones), GFP_KERNEL);
>> +	if (!device->empty_zones)
>> +		return -ENOMEM;
> 
> This leaks device->seq_zones from the current context, though thre are
> calls to btrfs_destroy_dev_zonetypes that would clean it up eventually.
> It'd be better to clean up here instead of relying on the caller.

Exactly.

>> +
>> +#define BTRFS_REPORT_NR_ZONES   4096
> 
> Please move this to the begining of the file if this is just local to
> the .c file and put a short comment explaining the meaning.
> 
>> +
>> +	/* Get zones type */
>> +	while (sector < nr_sectors) {
>> +		nr_zones = BTRFS_REPORT_NR_ZONES;
>> +		ret = __btrfs_get_dev_zones(device, sector << SECTOR_SHIFT,
>> +					    &zones, &nr_zones, GFP_KERNEL);
>> +		if (ret != 0 || !nr_zones) {
>> +			if (!ret)
>> +				ret = -EIO;
>> +			goto out;
>> +		}
>> +
>> +		for (i = 0; i < nr_zones; i++) {
>> +			if (zones[i].type == BLK_ZONE_TYPE_SEQWRITE_REQ)
>> +				set_bit(n, device->seq_zones);
>> +			if (zones[i].cond == BLK_ZONE_COND_EMPTY)
>> +				set_bit(n, device->empty_zones);
>> +			sector = zones[i].start + zones[i].len;
>> +			n++;
>> +		}
>> +	}
>> +
>> +	if (n != device->nr_zones) {
>> +		btrfs_err(device->fs_info,
>> +			  "Inconsistent number of zones (%u / %u)\n", n,
> 
> lowercase and no "\n"
> 
>> +			  device->nr_zones);
>> +		ret = -EIO;
>> +		goto out;
>> +	}
>> +
>> +	btrfs_info(device->fs_info,
>> +		   "host-%s zoned block device, %u zones of %llu sectors\n",
>> +		   bdev_zoned_model(bdev) == BLK_ZONED_HM ? "managed" : "aware",
>> +		   device->nr_zones, device->zone_size >> SECTOR_SHIFT);
>> +
>> +out:
>> +	kfree(zones);
>> +
>> +	if (ret)
>> +		btrfs_destroy_dev_zonetypes(device);
>> +
>> +	return ret;
>> +}
>> +
>>   static int btrfs_open_one_device(struct btrfs_fs_devices *fs_devices,
>>   			struct btrfs_device *device, fmode_t flags,
>>   			void *holder)
>> @@ -842,6 +971,11 @@ static int btrfs_open_one_device(struct btrfs_fs_devices *fs_devices,
>>   	clear_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state);
>>   	device->mode = flags;
>>   
>> +	/* Get zone type information of zoned block devices */
>> +	ret = btrfs_get_dev_zonetypes(device);
>> +	if (ret != 0)
>> +		goto error_brelse;
>> +
>>   	fs_devices->open_devices++;
>>   	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) &&
>>   	    device->devid != BTRFS_DEV_REPLACE_DEVID) {
>> @@ -1243,6 +1377,7 @@ static void btrfs_close_bdev(struct btrfs_device *device)
>>   	}
>>   
>>   	blkdev_put(device->bdev, device->mode);
>> +	btrfs_destroy_dev_zonetypes(device);
>>   }
>>   
>>   static void btrfs_close_one_device(struct btrfs_device *device)
>> @@ -2664,6 +2799,13 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
>>   	mutex_unlock(&fs_info->chunk_mutex);
>>   	mutex_unlock(&fs_devices->device_list_mutex);
>>   
>> +	/* Get zone type information of zoned block devices */
>> +	ret = btrfs_get_dev_zonetypes(device);
>> +	if (ret) {
>> +		btrfs_abort_transaction(trans, ret);
>> +		goto error_sysfs;
> 
> Can this be moved before the locked section so that any failure does not
> lead to transaction abort?
> 
> The function returns ENOMEM that does not necessarily need to kill the
> filesystem. And EIO which means that some faulty device is being added
> to the filesystem but this again should fail early.

OK. I can move that before the transaction starts.

>> +	}
>> +
>>   	if (seeding_dev) {
>>   		mutex_lock(&fs_info->chunk_mutex);
>>   		ret = init_first_rw_device(trans);
>> @@ -2729,6 +2871,7 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
>>   	return ret;
>>   
>>   error_sysfs:
>> +	btrfs_destroy_dev_zonetypes(device);
>>   	btrfs_sysfs_rm_device_link(fs_devices, device);
>>   	mutex_lock(&fs_info->fs_devices->device_list_mutex);
>>   	mutex_lock(&fs_info->chunk_mutex);
>> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
>> index b8a0e8d0672d..1599641e216c 100644
>> --- a/fs/btrfs/volumes.h
>> +++ b/fs/btrfs/volumes.h
>> @@ -62,6 +62,16 @@ struct btrfs_device {
>>   
>>   	struct block_device *bdev;
>>   
>> +	/*
>> +	 * Number of zones, zone size and types of zones if bdev is a
>> +	 * zoned block device.
>> +	 */
>> +	u64 zone_size;
>> +	u8  zone_size_shift;
> 
> So the zone_size is always power of two? I may be missing something, but
> I wonder if the calculations based on shifts are safe.

The kernel ZBD support have a restriction that
"The zone size must also be equal to a power of 2 number of logical blocks."
http://zonedstorage.io/introduction/linux-support/#zbd-support-restrictions

So, the zone_size is guaranteed to be power of two.

>> +	u32 nr_zones;
>> +	unsigned long *seq_zones;
>> +	unsigned long *empty_zones;
>> +
>>   	/* the mode sent to blkdev_get */
>>   	fmode_t mode;
>>   
>> @@ -476,6 +486,28 @@ int btrfs_finish_chunk_alloc(struct btrfs_trans_handle *trans,
>>   int btrfs_remove_chunk(struct btrfs_trans_handle *trans, u64 chunk_offset);
>>   struct extent_map *btrfs_get_chunk_map(struct btrfs_fs_info *fs_info,
>>   				       u64 logical, u64 length);
>> +int btrfs_get_dev_zone(struct btrfs_device *device, u64 pos,
>> +		       struct blk_zone *zone, gfp_t gfp_mask);
>> +
>> +static inline int btrfs_dev_is_sequential(struct btrfs_device *device, u64 pos)
>> +{
>> +	unsigned int zno = pos >> device->zone_size_shift;
> 
> The types don't match here, pos is u64 and I'm not sure if it's
> guaranteed that the value after shift will fit ti unsigned int.
> 
>> +
>> +	if (!device->seq_zones)
>> +		return 1;
>> +
>> +	return test_bit(zno, device->seq_zones);
>> +}
>> +
>> +static inline int btrfs_dev_is_empty_zone(struct btrfs_device *device, u64 pos)
>> +{
>> +	unsigned int zno = pos >> device->zone_size_shift;
> 
> Same.

I will fix.