Re: io_uring_prep_openat_direct() and link/drain

[Jens Axboe <axboe@kernel.dk>]

On 4/1/22 10:02 AM, Miklos Szeredi wrote:
> On Fri, 1 Apr 2022 at 17:36, Jens Axboe <axboe@kernel.dk> wrote:
> 
>> I take it you're continually reusing those slots?
> 
> Yes.
> 
>>  If you have a test
>> case that'd be ideal. Agree that it sounds like we just need an
>> appropriate breather to allow fput/task_work to run. Or it could be the
>> deferral free of the fixed slot.
> 
> Adding a breather could make the worst case latency be large.  I think
> doing the fput synchronously would be better in general.

fput() isn't sync, it'll just offload to task_work. There are some
dependencies there that would need to be checked. But we'll find a way
to deal with it.

> I test this on an VM with 8G of memory and run the following:
> 
> ./forkbomb 14 &
> # wait till 16k processes are forked
> for i in `seq 1 100`; do ./procreads u; done
> 
> You can compare performance with plain reads (./procreads p), the
> other tests don't work on public kernels.

OK, I'll check up on this, but probably won't have time to do so before
early next week.

-- 
Jens Axboe