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[5.186.127.235]) by smtp.gmail.com with ESMTPSA id j3sm10363857edr.87.2020.06.21.11.55.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 21 Jun 2020 11:55:06 -0700 (PDT) Date: Sun, 21 Jun 2020 20:55:05 +0200 From: "javier.gonz@samsung.com" To: Jens Axboe Cc: Matias =?utf-8?B?QmrDuHJsaW5n?= , Damien Le Moal , 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" Subject: Re: [PATCH 3/3] io_uring: add support for zone-append Message-ID: <20200621185505.4i46y4kndzvqlzdm@MacBook-Pro.localdomain> References: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 19.06.2020 09:44, Jens Axboe wrote: >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. Sounds good. Thanks Matias too for chipping in with more ideas. We have enough for a v2. Javier