Re: [PATCH v3 4/4] io_uring: add support for zone-append

Jens Axboe
2020-07-09T13:58:09Z

On 7/9/20 4:15 AM, Christoph Hellwig wrote:
> On Sun, Jul 05, 2020 at 03:00:47PM -0600, Jens Axboe wrote:
>>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>>> index 155f3d8..cbde4df 100644
>>> --- a/fs/io_uring.c
>>> +++ b/fs/io_uring.c
>>> @@ -402,6 +402,8 @@ struct io_rw {
>>> struct kiocb kiocb;
>>> u64 addr;
>>> u64 len;
>>> + /* zone-relative offset for append, in sectors */
>>> + u32 append_offset;
>>> };
>>
>> I don't like this very much at all. As it stands, the first cacheline
>> of io_kiocb is set aside for request-private data. io_rw is already
>> exactly 64 bytes, which means that you're now growing io_rw beyond
>> a cacheline and increasing the size of io_kiocb as a whole.
>>
>> Maybe you can reuse io_rw->len for this, as that is only used on the
>> submission side of things.
>
> We don't actually need any new field at all. By the time the write
> returned ki_pos contains the offset after the write, and the res
> argument to ->ki_complete contains the amount of bytes written, which
> allow us to trivially derive the starting position.

Then let's just do that instead of jumping through hoops either
justifying growing io_rw/io_kiocb or turning kiocb into a global
completion thing.

--
Jens Axboe