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From:   Damien Le Moal <Damien.LeMoal@wdc.com>
To:     =?iso-8859-1?Q?Matias_Bj=F8rling?= <mb@lightnvm.io>,
        Kanchan Joshi <joshi.k@samsung.com>
CC:     "axboe@kernel.dk" <axboe@kernel.dk>,
        "viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
        "bcrl@kvack.org" <bcrl@kvack.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
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        "javier.gonz@samsung.com" <javier.gonz@samsung.com>,
        Keith Busch <Keith.Busch@wdc.com>,
        Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 0/3] zone-append support in aio and io-uring
Thread-Topic: [PATCH 0/3] zone-append support in aio and io-uring
Thread-Index: AQHWRMyErNBfEVsLrU+xBQX5pX+rOw==
Date:   Fri, 19 Jun 2020 01:03:34 +0000
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On 2020/06/19 5:04, Matias Bj=F8rling wrote:=0A=
> On 18/06/2020 21.21, Kanchan Joshi wrote:=0A=
>> On Thu, Jun 18, 2020 at 10:04:32AM +0200, Matias Bj=F8rling wrote:=0A=
>>> On 17/06/2020 19.23, Kanchan Joshi wrote:=0A=
>>>> This patchset enables issuing zone-append using aio and io-uring =0A=
>>>> direct-io interface.=0A=
>>>>=0A=
>>>> For aio, this introduces opcode IOCB_CMD_ZONE_APPEND. Application =0A=
>>>> uses start LBA=0A=
>>>> of the zone to issue append. On completion 'res2' field is used to =0A=
>>>> return=0A=
>>>> zone-relative offset.=0A=
>>>>=0A=
>>>> For io-uring, this introduces three opcodes: =0A=
>>>> IORING_OP_ZONE_APPEND/APPENDV/APPENDV_FIXED.=0A=
>>>> Since io_uring does not have aio-like res2, cqe->flags are =0A=
>>>> repurposed to return zone-relative offset=0A=
>>>=0A=
>>> Please provide a pointers to applications that are updated and ready =
=0A=
>>> to take advantage of zone append.=0A=
>>>=0A=
>>> I do not believe it's beneficial at this point to change the libaio =0A=
>>> API, applications that would want to use this API, should anyway =0A=
>>> switch to use io_uring.=0A=
>>>=0A=
>>> Please also note that applications and libraries that want to take =0A=
>>> advantage of zone append, can already use the zonefs file-system, as =
=0A=
>>> it will use the zone append command when applicable.=0A=
>>=0A=
>> AFAIK, zonefs uses append while serving synchronous I/O. And append bio=
=0A=
>> is waited upon synchronously. That maybe serving some purpose I do=0A=
>> not know currently. But it seems applications using zonefs file=0A=
>> abstraction will get benefitted if they could use the append =0A=
>> themselves to=0A=
>> carry the I/O, asynchronously.=0A=
> Yep, please see Christoph's comment regarding adding the support to zonef=
s.=0A=
=0A=
For the asynchronous processing of zone append in zonefs, we need to add=0A=
plumbing in the iomap code first. Since this is missing currently, zonefs c=
an=0A=
only do synchronous/blocking zone append for now. Will be working on that, =
if we=0A=
can come up with a semantic that makes sense for posix system calls. zonefs=
 is=0A=
not a posix compliant file system, so we are not strongly tied by posix=0A=
specifications. But we still want to make it as easy as possible to underst=
and=0A=
and use by the user.=0A=
=0A=
=0A=
-- =0A=
Damien Le Moal=0A=
Western Digital Research=0A=