Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v3 4/4] io_uring: add support for zone-append
To:     Christoph Hellwig <hch@infradead.org>,
        Kanchan Joshi <joshiiitr@gmail.com>
Cc:     Kanchan Joshi <joshi.k@samsung.com>, viro@zeniv.linux.org.uk,
        bcrl@kvack.org, Damien.LeMoal@wdc.com, asml.silence@gmail.com,
        linux-fsdevel@vger.kernel.org, Matias Bj??rling <mb@lightnvm.io>,
        linux-kernel@vger.kernel.org, linux-aio@kvack.org,
        io-uring@vger.kernel.org, linux-block@vger.kernel.org,
        Selvakumar S <selvakuma.s1@samsung.com>,
        Nitesh Shetty <nj.shetty@samsung.com>,
        Javier Gonzalez <javier.gonz@samsung.com>
References: <CGME20200705185227epcas5p16fba3cb92561794b960184c89fdf2bb7@epcas5p1.samsung.com>
 <1593974870-18919-5-git-send-email-joshi.k@samsung.com>
 <fe0066b7-5380-43ee-20b2-c9b17ba18e4f@kernel.dk>
 <20200709085501.GA64935@infradead.org>
 <adc14700-8e95-10b2-d914-afa5029ae80c@kernel.dk>
 <20200709140053.GA7528@infradead.org>
 <2270907f-670c-5182-f4ec-9756dc645376@kernel.dk>
 <CA+1E3r+H7WEyfTufNz3xBQQynOVV-uD3myYynkfp7iU+D=Svuw@mail.gmail.com>
 <f5e3e931-ef1b-2eb6-9a03-44dd5589c8d3@kernel.dk>
 <CA+1E3rLna6VVuwMSHVVEFmrgsTyJN=U4CcZtxSGWYr_UYV7AmQ@mail.gmail.com>
 <20200710131054.GB7491@infradead.org>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <9e870249-01db-c68d-ea65-28edc3c1f071@kernel.dk>
Date:   Fri, 10 Jul 2020 08:09:33 -0600
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.10.0
MIME-Version: 1.0
In-Reply-To: <20200710131054.GB7491@infradead.org>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 7/10/20 7:10 AM, Christoph Hellwig wrote:
> On Fri, Jul 10, 2020 at 12:35:43AM +0530, Kanchan Joshi wrote:
>> Append required special treatment (conversion for sector to bytes) for io_uring.
>> And we were planning a user-space wrapper to abstract that.
>>
>> But good part (as it seems now) was: append result went along with cflags at
>> virtually no additional cost. And uring code changes became super clean/minimal
>> with further revisions.
>> While indirect-offset requires doing allocation/mgmt in application,
>> io-uring submission
>> and in completion path (which seems trickier), and those CQE flags
>> still get written
>> user-space and serve no purpose for append-write.
> 
> I have to say that storing the results in the CQE generally make
> so much more sense.  I wonder if we need a per-fd "large CGE" flag
> that adds two extra u64s to the CQE, and some ops just require this
> version.

I have been pondering the same thing, we could make certain ops consume
two CQEs if it makes sense. It's a bit ugly on the app side with two
different CQEs for a request, though. We can't just treat it as a large
CQE, as they might not be sequential if we happen to wrap. But maybe
it's not too bad.

-- 
Jens Axboe