Re: [PATCH] zonefs: do not use append if device does not support it

[Andreas Hindborg (Samsung)]

Damien Le Moal <dlemoal@xxxxxxxxxx> writes:

> On 6/27/23 03:23, Andreas Hindborg (Samsung) wrote:
>> 
>> Johannes Thumshirn <Johannes.Thumshirn@xxxxxxx> writes:
>> 
>>> On 26.06.23 18:47, Andreas Hindborg wrote:
>>>> From: "Andreas Hindborg (Samsung)" <nmi@xxxxxxxxxxxx>
>>>>
>>>> Zonefs will try to use `zonefs_file_dio_append()` for direct sync writes even if
>>>> device `max_zone_append_sectors` is zero. This will cause the IO to fail as the
>>>> io vector is truncated to zero. It also causes a call to
>>>> `invalidate_inode_pages2_range()` with end set to UINT_MAX, which is probably
>>>> not intentional. Thus, do not use append when device does not support it.
>>>>
>>>
>>> I'm sorry but I think it has been stated often enough that for Linux Zone Append
>>> is a mandatory feature for a Zoned Block Device. Therefore this path is essentially
>>> dead code as max_zone_append_sectors will always be greater than zero.
>>>
>>> So this is a clear NAK from my side.
>> 
>> OK, thanks for clarifying 👍 I came across this bugging out while
>> playing around with zone append for ublk. The code makes sense if the
>> stack expects append to always be present.
>> 
>> I didn't follow the discussion, could you reiterate why the policy is
>> that zoned devices _must_ support append?
>
> To avoid support fragmentation and for performance. btrfs zoned block device
> support requires zone append and using that command makes writes much faster as
> we do not have to go through zone locking.
> Note that for zonefs, I plan to add async zone append support as well, linked
> with O_APPEND use to further improve write performance with ZNS drives.
>

Thanks for clarifying, Damien 👍

BR Andreas