linux-kernel - Re: [PATCH net-next v3 1/4] page_pool: frag API support for 32-bit arch with 64-bit DMA

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Message-ID: <1bbf2afa-91b2-a3d0-60e0-81cd386eb68d@gmail.com>
Date:   Sat, 10 Jun 2023 21:13:21 +0800
From:   Yunsheng Lin <yunshenglin0825@...il.com>
To:     Jesper Dangaard Brouer <jbrouer@...hat.com>,
        Yunsheng Lin <linyunsheng@...wei.com>, davem@...emloft.net,
        kuba@...nel.org, pabeni@...hat.com
Cc:     brouer@...hat.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky <leon@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        linux-rdma@...r.kernel.org
Subject: Re: [PATCH net-next v3 1/4] page_pool: frag API support for 32-bit
 arch with 64-bit DMA

On 2023/6/9 23:02, Jesper Dangaard Brouer wrote:
...

>>                    PP_FLAG_DMA_SYNC_DEV |\
>>                    PP_FLAG_PAGE_FRAG)
>>   +#define PAGE_POOL_DMA_USE_PP_FRAG_COUNT    \
>> +        (sizeof(dma_addr_t) > sizeof(unsigned long))
>> +
> 
> I have a problem with the name PAGE_POOL_DMA_USE_PP_FRAG_COUNT
> because it is confusing to read in an if-statement.

Actually, it is already in an if-statement before this patch:)
Maybe starting to use it in the driver is confusing to you?
If not, maybe we can keep it that for now, and change it when
we come up with a better name.

> 
> Proposals rename to:  DMA_OVERLAP_PP_FRAG_COUNT
>  Or:  MM_DMA_OVERLAP_PP_FRAG_COUNT
>  Or:  DMA_ADDR_OVERLAP_PP_FRAG_COUNT

It seems DMA_ADDR_OVERLAP_PP_FRAG_COUNT is better,
and DMA_ADDR_UPPER_OVERLAP_PP_FRAG_COUNT seems more accurate if a
longer macro name is not an issue here.

> 
> Notice how I also removed the prefix PAGE_POOL_ because this is a MM-layer constraint and not a property of page_pool.

I am not sure if it is a MM-layer constraint yet.
Do you mean 'MM-layer constraint' as 'struct page' not having
enough space for page pool with 32-bit arch with 64-bit DMA?
If that is the case, we may need a more generic name for that
constraint instead of 'DMA_ADDR_OVERLAP_PP_FRAG_COUNT'?

And a more generic name seems confusing for page pool too, as
it doesn't tell that we only have that problem for 32-bit arch
with 64-bit DMA.

So if the above makes sense, it seems we may need to keep the
PAGE_POOL_ prefix, which would be
'PAGE_POOL_DMA_ADDR_UPPER_OVERLAP_PP_FRAG_COUNT' if the long
name is not issue here.

Anyway, naming is hard, we may need a seperate patch to explain
it, which is not really related to this patchset IHMO, so I'd
rather keep it as before if we can not come up with a name which
is not confusing to most people.

> 
> 
> --Jesper
> 
>