Re: [PATCH net-next v6 3/5] page_pool: Allow drivers to hint on SKB recycling

[Tariq Toukan <ttoukan.linux@gmail.com>]

On 6/5/2021 7:34 PM, Matteo Croce wrote:
> On Sat, Jun 5, 2021 at 6:06 PM David Ahern <dsahern@gmail.com> wrote:
>>
>> On 6/4/21 2:42 AM, Ilias Apalodimas wrote:
>>> [...]
>>>>> +   /* Driver set this to memory recycling info. Reset it on recycle.
>>>>> +    * This will *not* work for NIC using a split-page memory model.
>>>>> +    * The page will be returned to the pool here regardless of the
>>>>> +    * 'flipped' fragment being in use or not.
>>>>> +    */
>>>>
>>>> I am not sure I understand how does the last part of comment related
>>>> to the code below, as there is no driver using split-page memory model
>>>> will reach here because those driver will not call skb_mark_for_recycle(),
>>>> right?
>>>>
>>>
>>> Yes the comment is there to prohibit people (mlx5 only actually) to add the
>>> recycling bit on their driver.  Because if they do it will *probably* work
>>> but they might get random corrupted packets which will be hard to debug.
>>>
>>
>> What's the complexity for getting it to work with split page model?
>> Since 1500 is the default MTU, requiring a page per packet means a lot
>> of wasted memory.
> 
> We could create a new memory model, e.g. MEM_TYPE_PAGE_SPLIT, and
> restore the behavior present in the previous versions of this serie,
> which is, save xdp_mem_info in struct page.
> As this could slightly impact the performances, this can be added in a
> future change when the drivers which are doing it want to use this
> recycling api.
> 

page-split model doesn't only help reduce memory waste, but increase 
cache-locality, especially for aggregated GRO SKBs.

I'm looking forward to integrating the page-pool SKB recycling API into 
mlx5e datapath. For this we need it to support the page-split model.

Let's see what's missing and how we can help making this happen.

Regards,
Tariq