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

Maciej Fijalkowski
2023-05-15T13:11:38Z

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
>