Re: [PATCH 09/19] btrfs: limit super block locations in HMZONED mode

[Anand Jain]

> On 28 Jun 2019, at 2:39 PM, Naohiro Aota <Naohiro.Aota@xxxxxxx> wrote:
> 
> On 2019/06/28 12:56, Anand Jain wrote:
>> On 7/6/19 9:10 PM, Naohiro Aota wrote:
>>> When in HMZONED mode, make sure that device super blocks are located in
>>> randomly writable zones of zoned block devices. That is, do not write super
>>> blocks in sequential write required zones of host-managed zoned block
>>> devices as update would not be possible.
>> 
>>   By design all copies of SB must be updated at each transaction,
>>   as they are redundant copies they must match at the end of
>>   each transaction.
>> 
>>   Instead of skipping the sb updates, why not alter number of
>>   copies at the time of mkfs.btrfs?
>> 
>> Thanks, Anand
> 
> That is exactly what the patched code does. It updates all the SB
> copies, but it just avoids writing a copy to sequential writing
> required zones. Mkfs.btrfs do the same. So, all the available SB
> copies always match after a transaction. At the SB location in a
> sequential write required zone, you will see zeroed region (in the
> next version of the patch series), but that is easy to ignore: it
> lacks even BTRFS_MAGIC.
> 

 Right, I saw the related Btrfs-progs patches at a later time,
 there are piles of emails after a vacation.;-)

> The number of SB copy available on HMZONED device will vary
> by its zone size and its zone layout.


Thanks, Anand

> Thanks,
> 
>> 
>>> Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx>
>>> Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
>>> ---
>>>   fs/btrfs/disk-io.c     | 11 +++++++++++
>>>   fs/btrfs/disk-io.h     |  1 +
>>>   fs/btrfs/extent-tree.c |  4 ++++
>>>   fs/btrfs/scrub.c       |  2 ++
>>>   4 files changed, 18 insertions(+)
>>> 
>>> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
>>> index 7c1404c76768..ddbb02906042 100644
>>> --- a/fs/btrfs/disk-io.c
>>> +++ b/fs/btrfs/disk-io.c
>>> @@ -3466,6 +3466,13 @@ struct buffer_head *btrfs_read_dev_super(struct block_device *bdev)
>>>   	return latest;
>>>   }
>>> 
>>> +int btrfs_check_super_location(struct btrfs_device *device, u64 pos)
>>> +{
>>> +	/* any address is good on a regular (zone_size == 0) device */
>>> +	/* non-SEQUENTIAL WRITE REQUIRED zones are capable on a zoned device */
>>> +	return device->zone_size == 0 || !btrfs_dev_is_sequential(device, pos);
>>> +}
>>> +
>>>   /*
>>>    * Write superblock @sb to the @device. Do not wait for completion, all the
>>>    * buffer heads we write are pinned.
>>> @@ -3495,6 +3502,8 @@ static int write_dev_supers(struct btrfs_device *device,
>>>   		if (bytenr + BTRFS_SUPER_INFO_SIZE >=
>>>   		    device->commit_total_bytes)
>>>   			break;
>>> +		if (!btrfs_check_super_location(device, bytenr))
>>> +			continue;
>>> 
>>>   		btrfs_set_super_bytenr(sb, bytenr);
>>> 
>>> @@ -3561,6 +3570,8 @@ static int wait_dev_supers(struct btrfs_device *device, int max_mirrors)
>>>   		if (bytenr + BTRFS_SUPER_INFO_SIZE >=
>>>   		    device->commit_total_bytes)
>>>   			break;
>>> +		if (!btrfs_check_super_location(device, bytenr))
>>> +			continue;
>>> 
>>>   		bh = __find_get_block(device->bdev,
>>>   				      bytenr / BTRFS_BDEV_BLOCKSIZE,
>>> diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
>>> index a0161aa1ea0b..70e97cd6fa76 100644
>>> --- a/fs/btrfs/disk-io.h
>>> +++ b/fs/btrfs/disk-io.h
>>> @@ -141,6 +141,7 @@ struct extent_map *btree_get_extent(struct btrfs_inode *inode,
>>>   		struct page *page, size_t pg_offset, u64 start, u64 len,
>>>   		int create);
>>>   int btrfs_get_num_tolerated_disk_barrier_failures(u64 flags);
>>> +int btrfs_check_super_location(struct btrfs_device *device, u64 pos);
>>>   int __init btrfs_end_io_wq_init(void);
>>>   void __cold btrfs_end_io_wq_exit(void);
>>> 
>>> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
>>> index 3d41d840fe5c..ae2c895d08c4 100644
>>> --- a/fs/btrfs/extent-tree.c
>>> +++ b/fs/btrfs/extent-tree.c
>>> @@ -267,6 +267,10 @@ static int exclude_super_stripes(struct btrfs_block_group_cache *cache)
>>>   			return ret;
>>>   	}
>>> 
>>> +	/* we won't have super stripes in sequential zones */
>>> +	if (cache->alloc_type == BTRFS_ALLOC_SEQ)
>>> +		return 0;
>>> +
>>>   	for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
>>>   		bytenr = btrfs_sb_offset(i);
>>>   		ret = btrfs_rmap_block(fs_info, cache->key.objectid,
>>> diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
>>> index f7b29f9db5e2..36ad4fad7eaf 100644
>>> --- a/fs/btrfs/scrub.c
>>> +++ b/fs/btrfs/scrub.c
>>> @@ -3720,6 +3720,8 @@ static noinline_for_stack int scrub_supers(struct scrub_ctx *sctx,
>>>   		if (bytenr + BTRFS_SUPER_INFO_SIZE >
>>>   		    scrub_dev->commit_total_bytes)
>>>   			break;
>>> +		if (!btrfs_check_super_location(scrub_dev, bytenr))
>>> +			continue;
>>> 
>>>   		ret = scrub_pages(sctx, bytenr, BTRFS_SUPER_INFO_SIZE, bytenr,
>>>   				  scrub_dev, BTRFS_EXTENT_FLAG_SUPER, gen, i,
>>> 
>> 
>> 
>