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

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Message-ID: <ZGIWZHNRvq5DSmeA@lore-desk>
Date: Mon, 15 May 2023 13:24:20 +0200
From: Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
To: Yunsheng Lin <linyunsheng@...wei.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 2023/5/12 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).

Regards,
Lorenzo


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