Re: [RFC v1] io_uring/rsrc: add fast path huge page handling in buffer registration

[Jens Axboe]

On 6/8/26 12:29 AM, sw.prabhu6@xxxxxxxxx wrote:
> From: Swarna Prabhu <sw.prabhu6@xxxxxxxxx>
> 
> io_uring sqe buffer registration path returns pinned user pages in 4k
> granularity. If the first pinned page is in a hugetlb folio and
> pages[nr_pages - 1] is also in the same folio then store a single page
> entry and report *npages = 1 while dropping nr_pages - 1 of the pin
> references it took earlier.
> 
> io_uring has support to identify and coalesce multi-hugepage-backed
> fixed buffers from the function 'io_check_coalesce_buffer()'. However
> we need to iterate over the entire page array and this patch bypasses
> the additional checks for this case. The fast path reduces the overall
> sqe buffer registration time that are backed by huge pages.
> 
> Measured with fio on bare metal backed by 1024 boot-allocated 2MB hugetlb
> pages and setting the cpu cores to governor for max performance.
> (hugepages=1024,hugepage_size=2M):
>   fio --ioengine=io_uring --rw=randwrite --bs=1M --size=2G --iodepth=256
>   --direct=1 --numjobs=5 --fixedbufs=1 --registerfiles=1 --iomem=mmaphuge
>   --hugepage-size=2M.
> 
> Avg across 3 runs:
> Metric                          Upstream(7.1-rc1)  Patched    Delta
> Reg time(io_sqe_buffer_register): 3797ns            2970ns   -21.8%
> Total reg for workload:           14.35ms           11.34ms  -21.9%
> fio write bandwidth:              1416MiB/s   1416MiB/s    No regression

This looks pretty reasonable. Curious what inspired this change though?
Workloads that register and unregister huge page backed buffers at
a rapid pace? The registration path should obviously not be slower than
it needs to on purpose, but it should also not be part of the application
fast path in general. I'd expect most users to register their IO memory
pool upfront and then never really touch it.

Can you expand on the background that led to this?

> Signed-off-by: Swarna Prabhu <s.prabhu@xxxxxxxxxxx>

This doesn't match your From: in the patch, that would need to be
corrected.

-- 
Jens Axboe