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

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Date:	Mon, 11 Apr 2016 09:53:54 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	Mel Gorman <mgorman@...hsingularity.net>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Brenden Blanco <bblanco@...mgrid.com>,
	lsf@...ts.linux-foundation.org, linux-mm <linux-mm@...ck.org>,
	Mel Gorman <mgorman@...e.de>,
	Tom Herbert <tom@...bertland.com>,
	lsf-pc@...ts.linux-foundation.org,
	Alexei Starovoitov <alexei.starovoitov@...il.com>
Subject: Re: [Lsf] [Lsf-pc] [LSF/MM TOPIC] Generic page-pool recycle
 facility?

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...

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.

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 ;)