linux-kernel - Re: [PATCH net-next v12 06/13] page

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Date: Mon, 24 Jun 2024 01:12:46 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: Mina Almasry <almasrymina@...gle.com>
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Subject: Re: [PATCH net-next v12 06/13] page_pool: devmem support

On 6/21/24 19:48, Mina Almasry wrote:
> On Mon, Jun 17, 2024 at 7:17 AM Pavel Begunkov <asml.silence@...il.com> wrote:
...
>>>    static inline unsigned long netmem_to_pfn(netmem_ref netmem)
>>>    {
>>> +     if (netmem_is_net_iov(netmem))
>>> +             return 0;
>>
>> IIRC 0 is a valid pfn. Not much of a concern since it's
>> used only for tracing, but might make sense to pass some
>> invalid pfn if there is one
>>
> 
> AFAIU all non-negative pfns are technically valid pfns if the machine
> is big enough.
> 
> I could have this function return long long instead of unsigned long
> so I can return a negative number for errors, and then cast to
> unsigned long when I figure out it's actually a pfn. Seemed like such
> a hassle especially since the call site is just tracing that I figured
> it's not that worth it.

Yeah, sounds like an overkill for tracing

> 
>>> +
>>>        return page_to_pfn(netmem_to_page(netmem));
>>>    }
>>>
>> ...
>>>    static inline netmem_ref netmem_compound_head(netmem_ref netmem)
>>>    {
>>> +     /* niov are never compounded */
>>> +     if (netmem_is_net_iov(netmem))
>>> +             return netmem;
>>> +
>>>        return page_to_netmem(compound_head(netmem_to_page(netmem)));
>>>    }
>>>
>>> +static inline void *netmem_address(netmem_ref netmem)
>>
>> I don't think it's used anywhere, do I miss it?
>>
> 
> Ah, It's used by the GVE devmem implementation:
> https://github.com/mina/linux/commit/da89baa81873d457cbf7b49ee6b4f0d66855b205
> 
> I could leave it out of this patch, then add it with the follow up GVE
> devmem implementation, but I figured almost for sure drivers are going
> to need this eventually, and it's small, so just put it here.

Either way is fine by me, checking the function is not leftovers

-- 
Pavel Begunkov