Re: [PATCH 0/4] io_uring: add IORING_OP_READ[WRITE]_SPLICE_BUF

Jens Axboe
2023-02-10T22:19:48Z

On 2/10/23 2:54 PM, Jens Axboe wrote:
> On 2/10/23 8:32 AM, Ming Lei wrote:
>> Hello,
>>
>> Add two OPs which buffer is retrieved via kernel splice for supporting
>> fuse/ublk zero copy.
>>
>> The 1st patch enhances direct pipe & splice for moving pages in kernel,
>> so that the two added OPs won't be misused, and avoid potential security
>> hole.
>>
>> The 2nd patch allows splice_direct_to_actor() caller to ignore signal
>> if the actor won't block and can be done in bound time.
>>
>> The 3rd patch add the two OPs.
>>
>> The 4th patch implements ublk's ->splice_read() for supporting
>> zero copy.
>>
>> ublksrv(userspace):
>>
>> https://github.com/ming1/ubdsrv/commits/io_uring_splice_buf
>>
>> So far, only loop/null target implements zero copy in above branch:
>>
>> ublk add -t loop -f $file -z
>> ublk add -t none -z
>>
>> Basic FS/IO function is verified, mount/kernel building & fio
>> works fine, and big chunk IO(BS: 64k/512k) performance gets improved
>> obviously.
>
> Do you have any performance numbers? Also curious on liburing regression
> tests, would be nice to see as it helps with review.
>
> Caveat - haven't looked into this in detail just yet.

Also see the recent splice/whatever discussion, might be something
that's relevant here, particularly if we can avoid splice:

https://lore.kernel.org/io-uring/0cfd9f02-dea7-90e2-e932-c8129b6013c7@samba.org/

It's long...

--
Jens Axboe