Messages in this thread | | | Date | Sun, 21 Jun 2020 20:52:07 +0200 | From | "" <> | Subject | Re: [PATCH 3/3] io_uring: add support for zone-append |
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On 19.06.2020 09:02, Jens Axboe wrote: >On 6/19/20 8:59 AM, Pavel Begunkov wrote: >> On 19/06/2020 17:15, Jens Axboe wrote: >>> On 6/19/20 3:41 AM, 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. >>> >>> If you need 64-bit of return value, then it's not going to work. Even >>> with the existing patches, reusing cqe->flags isn't going to fly, as >>> it would conflict with eg doing zone append writes with automatic >>> buffer selection. >> >> Buffer selection is for reads/recv kind of requests, but appends >> are writes. In theory they can co-exist using cqe->flags. > >Yeah good point, since it's just writes, doesn't matter. But the other >point still stands, it could potentially conflict with other flags, but >I guess only to the extent where both flags would need extra storage in >->flags. So not a huge concern imho.
Very good point Pavel!
If co-existing with the current flags is an option, I'll explore this for the next version.
Thanks Jens and Pavel for the time and ideas!
Javier
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