linux-kernel - Re: [PATCH RFC net-next v4 6/9] iavf: switch to Page Pool

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Date:   Tue, 18 Jul 2023 15:56:45 +0200
From:   Alexander Lobakin <aleksander.lobakin@...el.com>
To:     Yunsheng Lin <linyunsheng@...wei.com>
CC:     Yunsheng Lin <yunshenglin0825@...il.com>,
        "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>,
        Michal Kubiak <michal.kubiak@...el.com>,
        Larysa Zaremba <larysa.zaremba@...el.com>,
        Alexander Duyck <alexanderduyck@...com>,
        David Christensen <drc@...ux.vnet.ibm.com>,
        "Jesper Dangaard Brouer" <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Paul Menzel <pmenzel@...gen.mpg.de>, <netdev@...r.kernel.org>,
        <intel-wired-lan@...ts.osuosl.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC net-next v4 6/9] iavf: switch to Page Pool

From: Yunsheng Lin <linyunsheng@...wei.com>
Date: Tue, 11 Jul 2023 19:47:14 +0800

> On 2023/7/10 21:34, Alexander Lobakin wrote:
>> From: Yunsheng Lin <yunshenglin0825@...il.com>
>> Date: Sun, 9 Jul 2023 13:16:39 +0800
>>
>>> On 2023/7/7 0:38, Alexander Lobakin wrote:
>>>
>>> ...
>>>  
>>>>>
>>>>>>  /**
>>>>>> @@ -766,13 +742,19 @@ void iavf_free_rx_resources(struct iavf_ring *rx_ring)
>>>>>>   **/
>>>>>>  int iavf_setup_rx_descriptors(struct iavf_ring *rx_ring)
>>>>>>  {
>>>>>> -	struct device *dev = rx_ring->dev;
>>>>>> -	int bi_size;
>>>>>> +	struct page_pool *pool;
>>>>>> +
>>>>>> +	pool = libie_rx_page_pool_create(&rx_ring->q_vector->napi,
>>>>>> +					 rx_ring->count);
>>>>>
>>>>> If a page is able to be spilt between more than one desc, perhaps the
>>>>> prt_ring size does not need to be as big as rx_ring->count.
>>>>
>>>> But we doesn't know in advance, right? Esp. given that it's hidden in
>>>> the lib. But anyway, you can only assume that in regular cases if you
>>>> always allocate frags of the same size, PP will split pages when 2+
>>>> frags can fit there or return the whole page otherwise, but who knows
>>>> what might happen.
>>>
>>> It seems intel driver is able to know the size of memory it needs when
>>> creating the ring/queue/napi/pp, maybe the driver only tell the libie
>>> how many descs does it use for queue, and libie can adjust it accordingly?
>>
>> But libie can't say for sure how PP will split pages for it, right?
>>
>>>
>>>> BTW, with recent recycling optimization, most of recycling is done
>>>> directly through cache, not ptr_ring. So I'd even say it's safe to start
>>>> creating smaller ptr_rings in the drivers.
>>>
>>> The problem is that we may use more memory than before for certain case
>>> if we don't limit the size of ptr_ring, unless we can ensure all of
>>> recycling is done directly through cache, not ptr_ring.
>> Also not sure I'm following =\
> 
> Before adding page pool support, the max memory used in the driver is as
> below:
> rx_ring->count * PAGE_SIZE;
> 
> After adding page pool support, the max memory used in the driver is as
> below:
> 
> ptr_ring->size * PAGE_SIZE +
> PP_ALLOC_CACHE_SIZE * PAGE_SIZE +
> rx_ring->count * PAGE_SIZE / pp.init_arg

I know. I was wondering how your message connects with what I said
regarding that using direct recycling more aggressively allows us to
reduce ptr_ring sizes, as e.g. on my setup ptr_ring is not used at all
(it still will be in other cases, but a lot less often than before).

> 
>>
>> [...]
>>
>> Thanks,
>> Olek
>>
>> .
>>

Thanks,
Olek