netdev - Re: [RFC net-next] net: veth: reduce page_pool memory footprint using half page per-buffer

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Date: Tue, 16 May 2023 20:55:21 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
CC: Lorenzo Bianconi <lorenzo@...nel.org>, <netdev@...r.kernel.org>,
	<bpf@...r.kernel.org>, <davem@...emloft.net>, <edumazet@...gle.com>,
	<kuba@...nel.org>, <pabeni@...hat.com>, <ast@...nel.org>,
	<daniel@...earbox.net>, <hawk@...nel.org>, <john.fastabend@...il.com>
Subject: Re: [RFC net-next] net: veth: reduce page_pool memory footprint using
 half page per-buffer

On 2023/5/15 19:24, Lorenzo Bianconi wrote:
>> On 2023/5/12 21:08, Lorenzo Bianconi wrote:
>>> In order to reduce page_pool memory footprint, rely on
>>> page_pool_dev_alloc_frag routine and reduce buffer size
>>> (VETH_PAGE_POOL_FRAG_SIZE) to PAGE_SIZE / 2 in order to consume one page
>>
>> Is there any performance improvement beside the memory saving? As it
>> should reduce TLB miss, I wonder if the TLB miss reducing can even
>> out the cost of the extra frag reference count handling for the
>> frag support?
> 
> reducing the requested headroom to 192 (from 256) we have a nice improvement in
> the 1500B frame case while it is mostly the same in the case of paged skb
> (e.g. MTU 8000B).
> 
>>
>>> for two 1500B frames. Reduce VETH_XDP_PACKET_HEADROOM to 192 from 256
>>> (XDP_PACKET_HEADROOM) to fit max_head_size in VETH_PAGE_POOL_FRAG_SIZE.
>>> Please note, using default values (CONFIG_MAX_SKB_FRAGS=17), maximum
>>> supported MTU is now reduced to 36350B.
>>
>> Maybe we don't need to limit the frag size to VETH_PAGE_POOL_FRAG_SIZE,
>> and use different frag size depending on the mtu or packet size?
>>
>> Perhaps the page_pool_dev_alloc_frag() can be improved to return non-frag
>> page if the requested frag size is larger than a specified size too.
>> I will try to implement it if the above idea makes sense.
>>
> 
> since there are no significant differences between full page and fragmented page
> implementation if the MTU is over the page boundary, does it worth to do so?
> (at least for the veth use-case).

Yes, as there is no significant differences between full page and fragmented page
implementation, unifying the interface is trivial, I have sent a RFC for that.
Using that interface may solve the supported mtu reducing problem at least.

> 
> Regards,
> Lorenzo
>