netdev - Re: [Lsf] [Lsf-pc] [LSF/MM TOPIC] Generic page-pool recycle facility?

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Message-ID: <1460409278.6473.567.camel@edumazet-glaptop3.roam.corp.google.com>
Date:	Mon, 11 Apr 2016 14:14:38 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	lsf@...ts.linux-foundation.org,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Brenden Blanco <bblanco@...mgrid.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	linux-mm <linux-mm@...ck.org>, Mel Gorman <mgorman@...e.de>,
	Tom Herbert <tom@...bertland.com>,
	lsf-pc@...ts.linux-foundation.org,
	Mel Gorman <mgorman@...hsingularity.net>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Alexander Duyck <alexander.duyck@...il.com>,
	"Waskiewicz, PJ" <PJ.Waskiewicz@...app.com>
Subject: Re: [Lsf] [Lsf-pc] [LSF/MM TOPIC] Generic page-pool recycle
 facility?

On Mon, 2016-04-11 at 21:47 +0200, Jesper Dangaard Brouer wrote:
> On Mon, 11 Apr 2016 09:53:54 -0700
> Eric Dumazet <eric.dumazet@...il.com> wrote:
> 
> > On Mon, 2016-04-11 at 18:19 +0200, Jesper Dangaard Brouer wrote:
> > 
> > > Drivers also do tricks where they fallback to smaller order pages. E.g.
> > > lookup function mlx4_alloc_pages().  I've tried to simulate that
> > > function here:
> > > https://github.com/netoptimizer/prototype-kernel/blob/91d323fc53/kernel/mm/bench/page_bench01.c#L69  
> > 
> > We use order-0 pages on mlx4 at Google, as order-3 pages are very
> > dangerous for some kind of attacks...
> 
> Interesting!
> 
> > An out of order TCP packet can hold an order-3 pages, while claiming to
> > use 1.5 KBvia skb->truesize.
> > 
> > order-0 only pages allow the page recycle trick used by Intel driver,
> > and we hardly see any page allocations in typical workloads.
> 
> Yes, I looked at the Intel ixgbe drivers page recycle trick. 
> 
> It is actually quite cool, but code wise it is a little hard to
> follow.  I started to look at the variant in i40e, specifically
> function i40e_clean_rx_irq_ps() explains it a bit more explicit.
>  
> 
> > While order-3 pages are 'nice' for friendly datacenter kind of
> > traffic, they also are a higher risk on hosts connected to the wild
> > Internet.
> > 
> > Maybe I should upstream this patch ;)
> 
> Definitely!
> 
> Does this patch also include a page recycle trick?  Else how do you get
> around the cost of allocating a single order-0 page?
> 

Yes, we use the page recycle trick.

Obviously not on powerpc (or any arch with PAGE_SIZE >= 8192), but
definitely on x86.