Re: [PATCH v4 03/27] btrfs: Check and enable HMZONED mode

From: Naohiro Aota <naohiro.aota@wdc.com>
To: Johannes Thumshirn <jthumshirn@suse.de>
Cc: linux-btrfs@vger.kernel.org, David Sterba <dsterba@suse.com>,
	Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>,
	Nikolay Borisov <nborisov@suse.com>,
	Damien Le Moal <damien.lemoal@wdc.com>,
	Matias Bjorling <Matias.Bjorling@wdc.com>,
	Hannes Reinecke <hare@suse.com>,
	Anand Jain <anand.jain@oracle.com>,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v4 03/27] btrfs: Check and enable HMZONED mode
Date: Mon, 26 Aug 2019 17:38:30 +0900	[thread overview]
Message-ID: <20190826083830.3dvajoi3dnu3nrr5@naota.dhcp.fujisawa.hgst.com> (raw)
In-Reply-To: <9c947b6c-c74d-24eb-ff6b-b448c8acfa40@suse.de>

On Fri, Aug 23, 2019 at 02:07:05PM +0200, Johannes Thumshirn wrote:
>On 23/08/2019 12:10, Naohiro Aota wrote:
>> HMZONED mode cannot be used together with the RAID5/6 profile for now.
>> Introduce the function btrfs_check_hmzoned_mode() to check this. This
>> function will also check if HMZONED flag is enabled on the file system and
>> if the file system consists of zoned devices with equal zone size.
>>
>> Additionally, as updates to the space cache are in-place, the space cache
>> cannot be located over sequential zones and there is no guarantees that the
>> device will have enough conventional zones to store this cache. Resolve
>> this problem by disabling completely the space cache.  This does not
>completely disabling ~^
>
>> introduces any problems with sequential block groups: all the free space is
>introduce ~^
>
>> located after the allocation pointer and no free space before the pointer.
>                                           is located? ~^
>> There is no need to have such cache.

Thanks.

>> @@ -25,6 +27,7 @@ int btrfs_get_dev_zone(struct btrfs_device *device, u64 pos,
>>  		       struct blk_zone *zone, gfp_t gfp_mask);
>>  int btrfs_get_dev_zone_info(struct btrfs_device *device);
>>  void btrfs_destroy_dev_zone_info(struct btrfs_device *device);
>> +int btrfs_check_hmzoned_mode(struct btrfs_fs_info *fs_info);
>
>
>While we're at it, shouldn't all the functions in hmzoned.[ch] have a
>!CONFIG_BLK_DEV_ZONED compat wrapper and hmzoned.o is dependent on
>CONFIG_BLK_DEV_ZONED?

Exactly. It was broken on !CONFIG_BLK_DEV_ZONED as the bot pointed
out... I'll push them behind CONFIG_BLK_DEV_ZONED in the next
version.

>-- 
>Johannes Thumshirn                            SUSE Labs Filesystems
>jthumshirn@suse.de                                +49 911 74053 689
>SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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