Messages in this thread | | | Subject | Re: [PATCH 3/3] io_uring: add support for zone-append | From | Matias Bjørling <> | Date | Fri, 19 Jun 2020 17:40:27 +0200 |
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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 <selvakuma.s1@samsung.com> >>>>>>>>>> >>>>>>>>>> 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 <selvakuma.s1@samsung.com> >>>>>>>>>> Signed-off-by: Kanchan Joshi <joshi.k@samsung.com> >>>>>>>>>> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com> >>>>>>>>>> Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com> >>>>>>>>>> --- >>>>>>>>>> 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.
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