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

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Message-ID: <62654fa5-d3a2-4b81-af70-59c9e90db842@huawei.com>
Date: Mon, 15 May 2023 19:10:37 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Lorenzo Bianconi <lorenzo@...nel.org>, <netdev@...r.kernel.org>
CC: <lorenzo.bianconi@...hat.com>, <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?

> 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.