linux-kernel - Re: [PATCH net-next 5/9] page_pool: don't use driver-set flags field directly

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Message-ID: <a7782cf1-e04a-e274-6a87-4952008bcc0c@huawei.com>
Date:   Sat, 29 Jul 2023 19:40:32 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>
CC:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Larysa Zaremba <larysa.zaremba@...el.com>,
        Alexander Duyck <alexanderduyck@...com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Simon Horman <simon.horman@...igine.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 5/9] page_pool: don't use driver-set flags field
 directly

On 2023/7/28 22:03, Alexander Lobakin wrote:
> From: Yunsheng Lin <linyunsheng@...wei.com>
> Date: Fri, 28 Jul 2023 20:36:50 +0800
> 
>> On 2023/7/27 22:43, Alexander Lobakin wrote:
>>
>>>  
>>>  struct page_pool {
>>>  	struct page_pool_params p;
>>> -	long pad;
>>> +
>>> +	bool dma_map:1;				/* Perform DMA mapping */
>>> +	enum {
>>> +		PP_DMA_SYNC_ACT_DISABLED = 0,	/* Driver didn't ask to sync */
>>> +		PP_DMA_SYNC_ACT_DO,		/* Perform DMA sync ops */
>>> +	} dma_sync_act:1;
>>> +	bool page_frag:1;			/* Allow page fragments */
>>>  
>>
>> Isn't it more common or better to just remove the flags field in
>> 'struct page_pool_params' and pass the flags by parameter like
>> below, so that patch 4 is not needed?
>>
>> struct page_pool *page_pool_create(const struct page_pool_params *params,
>> 				   unsigned int	flags);
> 
> You would need a separate patch to convert all the page_pool_create()
> users then either way.
> And it doesn't look really natural to me to pass both driver-set params
> and driver-set flags as separate function arguments. Someone may then
> think "why aren't flags just put in the params itself". The fact that
> Page Pool copies the whole params in the page_pool struct after
> allocating it is internals, page_pool_create() prototype however isn't.
> Thoughts?

It just seems odd to me that dma_map and page_frag is duplicated as we
seems to have the same info in the page_pool->p.flags.

What about:
In [PATCH net-next 4/9] page_pool: shrink &page_pool_params a tiny bit,
'flags' is bit-field'ed with 'dma_dir', what about changing 'dma_dir'
to be bit-field'ed with 'dma_sync_act', so that page_pool->p.flags stays
the same as before, and 'dma_map' & 'page_frag' do not seems be really
needed as we have the same info in page_pool->p.flags?


> 
> Thanks,
> Olek
> 
> .
>