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Subject: Re: [PATCH 09/19] btrfs: limit super block locations in HMZONED mode
From:   Anand Jain <anand.jain@oracle.com>
In-Reply-To: <SN6PR04MB52315AB9E229D0BAAB930D5B8CFC0@SN6PR04MB5231.namprd04.prod.outlook.com>
Date:   Fri, 28 Jun 2019 14:52:40 +0800
Cc:     "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>,
        David Sterba <dsterba@suse.com>, Chris Mason <clm@fb.com>,
        Josef Bacik <josef@toxicpanda.com>, Qu Wenruo <wqu@suse.com>,
        Nikolay Borisov <nborisov@suse.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Hannes Reinecke <hare@suse.com>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        Damien Le Moal <Damien.LeMoal@wdc.com>,
        =?utf-8?Q?Matias_Bj=C3=B8rling?= <mb@lightnvm.io>,
        Johannes Thumshirn <jthumshirn@suse.de>,
        Bart Van Assche <bvanassche@acm.org>
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Message-Id: <57A75561-4582-4711-8A1E-1B45F673BF14@oracle.com>
References: <20190607131025.31996-1-naohiro.aota@wdc.com>
 <20190607131025.31996-10-naohiro.aota@wdc.com>
 <0ca3c475-fe10-4135-ddc9-7a82cc966d9a@oracle.com>
 <SN6PR04MB52315AB9E229D0BAAB930D5B8CFC0@SN6PR04MB5231.namprd04.prod.outlook.com>
To:     Naohiro Aota <Naohiro.Aota@wdc.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On 28 Jun 2019, at 2:39 PM, Naohiro Aota <Naohiro.Aota@wdc.com> wrote:
>=20
> 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.
>>=20
>>   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.
>>=20
>>   Instead of skipping the sb updates, why not alter number of
>>   copies at the time of mkfs.btrfs?
>>=20
>> Thanks, Anand
>=20
> 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.
>=20

 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,
>=20
>>=20
>>> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
>>> Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
>>> ---
>>>   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(+)
>>>=20
>>> 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;
>>>   }
>>>=20
>>> +int btrfs_check_super_location(struct btrfs_device *device, u64 =
pos)
>>> +{
>>> +	/* any address is good on a regular (zone_size =3D=3D 0) device =
*/
>>> +	/* non-SEQUENTIAL WRITE REQUIRED zones are capable on a zoned =
device */
>>> +	return device->zone_size =3D=3D 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 >=3D
>>>   		    device->commit_total_bytes)
>>>   			break;
>>> +		if (!btrfs_check_super_location(device, bytenr))
>>> +			continue;
>>>=20
>>>   		btrfs_set_super_bytenr(sb, bytenr);
>>>=20
>>> @@ -3561,6 +3570,8 @@ static int wait_dev_supers(struct btrfs_device =
*device, int max_mirrors)
>>>   		if (bytenr + BTRFS_SUPER_INFO_SIZE >=3D
>>>   		    device->commit_total_bytes)
>>>   			break;
>>> +		if (!btrfs_check_super_location(device, bytenr))
>>> +			continue;
>>>=20
>>>   		bh =3D __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);
>>>=20
>>> 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;
>>>   	}
>>>=20
>>> +	/* we won't have super stripes in sequential zones */
>>> +	if (cache->alloc_type =3D=3D BTRFS_ALLOC_SEQ)
>>> +		return 0;
>>> +
>>>   	for (i =3D 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
>>>   		bytenr =3D btrfs_sb_offset(i);
>>>   		ret =3D 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;
>>>=20
>>>   		ret =3D scrub_pages(sctx, bytenr, BTRFS_SUPER_INFO_SIZE, =
bytenr,
>>>   				  scrub_dev, BTRFS_EXTENT_FLAG_SUPER, =
gen, i,
>>>=20
>>=20
>>=20
>=20