Re: [PATCH v1 0/2] fuse io_uring: support registered buffers

[Bernd Schubert <bschubert@ddn.com>]

On 10/24/25 00:27, Joanne Koong wrote:
> On Wed, Oct 22, 2025 at 1:43 PM Bernd Schubert <bschubert@ddn.com> wrote:
>>
>> On 10/22/25 22:20, Joanne Koong wrote:
>>> This adds support for daemons who preregister buffers to minimize the overhead
>>> of pinning/unpinning user pages and translating virtual addresses. Registered
>>> buffers pay the cost once during registration then reuse the pre-pinned pages,
>>> which helps reduce the per-op overhead.
>>>
>>> This is on top of commit 211ddde0823f in the iouring tree.
>>
>> Interesting, on a first glance this looks like an alternative
>> implementation of page pinning
>>
>> https://lore.kernel.org/all/20240901-b4-fuse-uring-rfcv3-without-mmap-v3-17-9207f7391444@ddn.com/
>>
>> At DDN we are running with that patch (changed commit message) and another
>> one that avoids io_uring_cmd_complete_in_task() - with pinned pages
>> the IO submitting application can directly write into header and payload
>> (note that the latter also required pinned headers)
>>
>> Going to look into your approach tomorrow.
> 
> Thanks for taking a look when you get the chance. The libfuse changes
> are in this branch
> https://github.com/joannekoong/libfuse/tree/registered_buffers btw.

Sorry, still didn't manage another task for tomorrow. Btw, the reason
hadn't sent my patches is that I hadn't handled memory accounting yet.
And then got busy with other tasks for much too long...

I see in io_sqe_buffers_register() how that is done, although I'm 
confused why it first calls io_pin_pages() and only then accounts. I.e.
it can temporarily go above the limit - I wonder what happens if the 
user opens another application that time that just needs a little locked
memory...

In general I think your solution more complex than mine - I think I'm
going to update my patches (there are conflicts due to folio conversion)
and then we can compare.


Thanks,
Bernd