linux-kernel - Re: [PATCH 0/3] zone-append support in aio and io-uring

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Date:   Thu, 18 Jun 2020 22:04:30 +0200
From:   Matias Bjørling <mb@...htnvm.io>
To:     Kanchan Joshi <joshi.k@...sung.com>
Cc:     axboe@...nel.dk, viro@...iv.linux.org.uk, bcrl@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-aio@...ck.org, io-uring@...r.kernel.org,
        linux-block@...r.kernel.org, selvakuma.s1@...sung.com,
        nj.shetty@...sung.com, javier.gonz@...sung.com,
        Damien Le Moal <Damien.LeMoal@....com>,
        Keith Busch <keith.busch@....com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 0/3] zone-append support in aio and io-uring

On 18/06/2020 21.21, Kanchan Joshi wrote:
> On Thu, Jun 18, 2020 at 10:04:32AM +0200, Matias Bjørling wrote:
>> On 17/06/2020 19.23, Kanchan Joshi wrote:
>>> This patchset enables issuing zone-append using aio and io-uring 
>>> direct-io interface.
>>>
>>> For aio, this introduces opcode IOCB_CMD_ZONE_APPEND. Application 
>>> uses start LBA
>>> of the zone to issue append. On completion 'res2' field is used to 
>>> return
>>> zone-relative offset.
>>>
>>> For io-uring, this introduces three opcodes: 
>>> IORING_OP_ZONE_APPEND/APPENDV/APPENDV_FIXED.
>>> Since io_uring does not have aio-like res2, cqe->flags are 
>>> repurposed to return zone-relative offset
>>
>> Please provide a pointers to applications that are updated and ready 
>> to take advantage of zone append.
>>
>> I do not believe it's beneficial at this point to change the libaio 
>> API, applications that would want to use this API, should anyway 
>> switch to use io_uring.
>>
>> Please also note that applications and libraries that want to take 
>> advantage of zone append, can already use the zonefs file-system, as 
>> it will use the zone append command when applicable.
>
> AFAIK, zonefs uses append while serving synchronous I/O. And append bio
> is waited upon synchronously. That maybe serving some purpose I do
> not know currently. But it seems applications using zonefs file
> abstraction will get benefitted if they could use the append 
> themselves to
> carry the I/O, asynchronously.
Yep, please see Christoph's comment regarding adding the support to zonefs.