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Fri, 19 Jun 2020 08:44:14 -0700 (PDT) Subject: Re: [PATCH 3/3] io_uring: add support for zone-append To: =?UTF-8?Q?Matias_Bj=c3=b8rling?= , "javier.gonz@samsung.com" , Damien Le Moal Cc: Kanchan Joshi , "viro@zeniv.linux.org.uk" , "bcrl@kvack.org" , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-aio@kvack.org" , "io-uring@vger.kernel.org" , "linux-block@vger.kernel.org" , "selvakuma.s1@samsung.com" , "nj.shetty@samsung.com" References: <1592414619-5646-1-git-send-email-joshi.k@samsung.com> <1592414619-5646-4-git-send-email-joshi.k@samsung.com> <20200618083529.ciifu4chr4vrv2j5@mpHalley.local> <20200618091113.eu2xdp6zmdooy5d2@mpHalley.local> <20200619094149.uaorbger326s6yzz@mpHalley.local> <2ba2079c-9a5d-698a-a8f0-cbd6fdb9a9f0@lightnvm.io> <317fa6b5-ce64-114e-b34d-2be7b50c24f1@lightnvm.io> <26f41284-6e52-58d3-6119-8ed34511e5dc@kernel.dk> <87f750fb-d217-ab37-9790-de9ad1ef4a87@lightnvm.io> From: Jens Axboe Message-ID: Date: Fri, 19 Jun 2020 09:44:12 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <87f750fb-d217-ab37-9790-de9ad1ef4a87@lightnvm.io> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/19/20 9:40 AM, Matias Bjørling wrote: > On 19/06/2020 17.20, Jens Axboe wrote: >> On 6/19/20 9:14 AM, Matias Bjørling wrote: >>> On 19/06/2020 16.18, Jens Axboe wrote: >>>> On 6/19/20 5:15 AM, Matias Bjørling wrote: >>>>> On 19/06/2020 11.41, javier.gonz@samsung.com wrote: >>>>>> Jens, >>>>>> >>>>>> Would you have time to answer a question below in this thread? >>>>>> >>>>>> On 18.06.2020 11:11, javier.gonz@samsung.com wrote: >>>>>>> On 18.06.2020 08:47, Damien Le Moal wrote: >>>>>>>> On 2020/06/18 17:35, javier.gonz@samsung.com wrote: >>>>>>>>> On 18.06.2020 07:39, Damien Le Moal wrote: >>>>>>>>>> On 2020/06/18 2:27, Kanchan Joshi wrote: >>>>>>>>>>> From: Selvakumar S >>>>>>>>>>> >>>>>>>>>>> Introduce three new opcodes for zone-append - >>>>>>>>>>> >>>>>>>>>>> IORING_OP_ZONE_APPEND : non-vectord, similiar to >>>>>>>>>>> IORING_OP_WRITE >>>>>>>>>>> IORING_OP_ZONE_APPENDV : vectored, similar to IORING_OP_WRITEV >>>>>>>>>>> IORING_OP_ZONE_APPEND_FIXED : append using fixed-buffers >>>>>>>>>>> >>>>>>>>>>> Repurpose cqe->flags to return zone-relative offset. >>>>>>>>>>> >>>>>>>>>>> Signed-off-by: SelvaKumar S >>>>>>>>>>> Signed-off-by: Kanchan Joshi >>>>>>>>>>> Signed-off-by: Nitesh Shetty >>>>>>>>>>> Signed-off-by: Javier Gonzalez >>>>>>>>>>> --- >>>>>>>>>>> fs/io_uring.c | 72 >>>>>>>>>>> +++++++++++++++++++++++++++++++++++++++++-- >>>>>>>>>>> include/uapi/linux/io_uring.h | 8 ++++- >>>>>>>>>>> 2 files changed, 77 insertions(+), 3 deletions(-) >>>>>>>>>>> >>>>>>>>>>> diff --git a/fs/io_uring.c b/fs/io_uring.c >>>>>>>>>>> index 155f3d8..c14c873 100644 >>>>>>>>>>> --- a/fs/io_uring.c >>>>>>>>>>> +++ b/fs/io_uring.c >>>>>>>>>>> @@ -649,6 +649,10 @@ struct io_kiocb { >>>>>>>>>>> unsigned long fsize; >>>>>>>>>>> u64 user_data; >>>>>>>>>>> u32 result; >>>>>>>>>>> +#ifdef CONFIG_BLK_DEV_ZONED >>>>>>>>>>> + /* zone-relative offset for append, in bytes */ >>>>>>>>>>> + u32 append_offset; >>>>>>>>>> this can overflow. u64 is needed. >>>>>>>>> We chose to do it this way to start with because struct io_uring_cqe >>>>>>>>> only has space for u32 when we reuse the flags. >>>>>>>>> >>>>>>>>> We can of course create a new cqe structure, but that will come with >>>>>>>>> larger changes to io_uring for supporting append. >>>>>>>>> >>>>>>>>> Do you believe this is a better approach? >>>>>>>> The problem is that zone size are 32 bits in the kernel, as a number >>>>>>>> of sectors. >>>>>>>> So any device that has a zone size smaller or equal to 2^31 512B >>>>>>>> sectors can be >>>>>>>> accepted. Using a zone relative offset in bytes for returning zone >>>>>>>> append result >>>>>>>> is OK-ish, but to match the kernel supported range of possible zone >>>>>>>> size, you >>>>>>>> need 31+9 bits... 32 does not cut it. >>>>>>> Agree. Our initial assumption was that u32 would cover current zone size >>>>>>> requirements, but if this is a no-go, we will take the longer path. >>>>>> Converting to u64 will require a new version of io_uring_cqe, where we >>>>>> extend at least 32 bits. I believe this will need a whole new allocation >>>>>> and probably ioctl(). >>>>>> >>>>>> Is this an acceptable change for you? We will of course add support for >>>>>> liburing when we agree on the right way to do this. >>>>> I took a quick look at the code. No expert, but why not use the existing >>>>> userdata variable? use the lowest bits (40 bits) for the Zone Starting >>>>> LBA, and use the highest (24 bits) as index into the completion data >>>>> structure? >>>>> >>>>> If you want to pass the memory address (same as what fio does) for the >>>>> data structure used for completion, one may also play some tricks by >>>>> using a relative memory address to the data structure. For example, the >>>>> x86_64 architecture uses 48 address bits for its memory addresses. With >>>>> 24 bit, one can allocate the completion entries in a 32MB memory range, >>>>> and then use base_address + index to get back to the completion data >>>>> structure specified in the sqe. >>>> For any current request, sqe->user_data is just provided back as >>>> cqe->user_data. This would make these requests behave differently >>>> from everything else in that sense, which seems very confusing to me >>>> if I was an application writer. >>>> >>>> But generally I do agree with you, there are lots of ways to make >>>> < 64-bit work as a tag without losing anything or having to jump >>>> through hoops to do so. The lack of consistency introduced by having >>>> zone append work differently is ugly, though. >>>> >>> Yep, agree, and extending to three cachelines is big no-go. We could add >>> a flag that said the kernel has changes the userdata variable. That'll >>> make it very explicit. >> Don't like that either, as it doesn't really change the fact that you're >> now doing something very different with the user_data field, which is >> just supposed to be passed in/out directly. Adding a random flag to >> signal this behavior isn't very explicit either, imho. It's still some >> out-of-band (ish) notification of behavior that is different from any >> other command. This is very different from having a flag that says >> "there's extra information in this other field", which is much cleaner. >> > Ok. Then it's pulling in the bits from cqe->res and cqe->flags that you > mention in the other mail. Sounds good. I think that's the best approach, if we need > 32-bits. Maybe we can get by just using ->res, if we switch to multiples of 512b instead for the result like Pavel suggested. That'd provide enough room in ->res, and would be preferable imho. But if we do need > 32-bits, then we can use this approach. -- Jens Axboe