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

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Message-ID: <ZGIvbfPd46EIVZf/@boxer>
Date: Mon, 15 May 2023 15:11:09 +0200
From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To: Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
CC: Yunsheng Lin <linyunsheng@...wei.com>, 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 Mon, May 15, 2023 at 01:24:20PM +0200, 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).

Can you define 'nice improvement' ? ;)
Show us numbers or improvement in %.

> 
> > 
> > > 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
>