linux-kernel - Re: [RFC PATCH v2 0/2] introduce io_uring_cmd_import_fixed

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Message-ID: <fd3264c8-02be-4634-bab2-2ad00a40a1b7@gmail.com>
Date: Thu, 13 Mar 2025 13:17:44 +0000
From: Pavel Begunkov <asml.silence@...il.com>
To: Sidong Yang <sidong.yang@...iosa.ai>
Cc: Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>,
 Jens Axboe <axboe@...nel.dk>, linux-btrfs@...r.kernel.org,
 linux-kernel@...r.kernel.org, io-uring@...r.kernel.org
Subject: Re: [RFC PATCH v2 0/2] introduce io_uring_cmd_import_fixed_vec

On 3/13/25 13:15, Pavel Begunkov wrote:
> On 3/13/25 10:44, Sidong Yang wrote:
>> On Thu, Mar 13, 2025 at 08:57:45AM +0000, Pavel Begunkov wrote:
>>> On 3/12/25 14:23, Sidong Yang wrote:
>>>> This patche series introduce io_uring_cmd_import_vec. With this function,
>>>> Multiple fixed buffer could be used in uring cmd. It's vectored version
>>>> for io_uring_cmd_import_fixed(). Also this patch series includes a usage
>>>> for new api for encoded read in btrfs by using uring cmd.
>>>
>>> Pretty much same thing, we're still left with 2 allocations in the
>>> hot path. What I think we can do here is to add caching on the
>>> io_uring side as we do with rw / net, but that would be invisible
>>> for cmd drivers. And that cache can be reused for normal iovec imports.
>>>
>>> https://github.com/isilence/linux.git regvec-import-cmd
>>> (link for convenience)
>>> https://github.com/isilence/linux/tree/regvec-import-cmd
>>>
>>> Not really target tested, no btrfs, not any other user, just an idea.
>>> There are 4 patches, but the top 3 are of interest.
>>
>> Thanks, I justed checked the commits now. I think cache is good to resolve
>> this without allocation if cache hit. Let me reimpl this idea and test it
>> for btrfs.
> 
> Sure, you can just base on top of that branch, hashes might be
> different but it's identical to the base it should be on. Your
> v2 didn't have some more recent merged patches.

Jens' for-6.15/io_uring-reg-vec specifically, but for-next likely
has it merged.

-- 
Pavel Begunkov