Re: [PATCH v2 0/4] io_uring/rsrc: coalescing multi-hugepage registered buffers

[Chenliang Li <cliang01.li@samsung.com>]

On 2024-05-11 16:43 Jens Axboe wrote:
> On 5/10/24 11:52 PM, Chenliang Li wrote:
>> Registered buffers are stored and processed in the form of bvec array,
>> each bvec element typically points to a PAGE_SIZE page but can also work
>> with hugepages. Specifically, a buffer consisting of a hugepage is
>> coalesced to use only one hugepage bvec entry during registration.
>> This coalescing feature helps to save both the space and DMA-mapping time.
>> 
>> However, currently the coalescing feature doesn't work for multi-hugepage
>> buffers. For a buffer with several 2M hugepages, we still split it into
>> thousands of 4K page bvec entries while in fact, we can just use a
>> handful of hugepage bvecs.
>> 
>> This patch series enables coalescing registered buffers with more than
>> one hugepages. It optimizes the DMA-mapping time and saves memory for
>> these kind of buffers.

> This series looks much better. Do you have a stand-alone test case
> for this? We should have that in liburing. Then we can also augment it
> with edge cases to ensure this is all safe and sound.

Thanks! Yes, I have a liburing test case, will send it as a patch in V3.