Messages in this thread | | | Subject | Re: [PATCH 3/3] io_uring: add support for zone-append | From | Matias Bjørling <> | Date | Fri, 19 Jun 2020 17:14:48 +0200 |
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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.
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