Re: [RFC 1/2] io_uring: don't use kiocb.private to store buf_index

[Bijan Mottahedeh <bijan.mottahedeh@oracle.com>]

On 5/19/2020 3:20 PM, Jens Axboe wrote:
> On 5/19/20 4:07 PM, Jens Axboe wrote:
>> On 5/19/20 3:52 PM, Bijan Mottahedeh wrote:
>>> kiocb.private is used in iomap_dio_rw() so store buf_index separately.
>> Hmm, that's no good, the owner of the iocb really should own ->private
>> as well.
>>
>> The downside of this patch is that io_rw now spills into the next
>> cacheline, which propagates to io_kiocb as well. iocb has 4 bytes
>> of padding, but probably cleaner if we can stuff it into io_kiocb
>> instead. How about adding a u16 after opcode? There's a 2 byte
>> hole there, so it would not impact the size of io_kiocb.
> I applied your patch, but moved the buf_index to not grow the
> structure:
>
> https://git.kernel.dk/cgit/linux-block/commit/?h=io_uring-5.7&id=4f4eeba87cc731b200bff9372d14a80f5996b277
>

That works.

Thanks!

--bijan