netdev - Re: [PATCH net-next 1/3] net: allow > 0 order atomic page alloc in skb_page_frag

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Message-ID: <1387819838.12212.6.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Mon, 23 Dec 2013 09:30:38 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Michael Dalton <mwdalton@...gle.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Eric Dumazet <edumazet@...gle.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jason Wang <jasowang@...hat.com>,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH net-next 1/3] net: allow > 0 order atomic page alloc in
 skb_page_frag_refill

On Mon, 2013-12-23 at 14:53 +0200, Michael S. Tsirkin wrote:
> On Mon, Dec 16, 2013 at 04:16:27PM -0800, Michael Dalton wrote:
> > skb_page_frag_refill currently permits only order-0 page allocs
> > unless GFP_WAIT is used. Change skb_page_frag_refill to attempt
> > higher-order page allocations whether or not GFP_WAIT is used. If
> > memory cannot be allocated, the allocator will fall back to
> > successively smaller page allocs (down to order-0 page allocs).
> > 
> > This change brings skb_page_frag_refill in line with the existing
> > page allocation strategy employed by netdev_alloc_frag, which attempts
> > higher-order page allocations whether or not GFP_WAIT is set, falling
> > back to successively lower-order page allocations on failure. Part
> > of migration of virtio-net to per-receive queue page frag allocators.
> > 
> > Signed-off-by: Michael Dalton <mwdalton@...gle.com>
> 
> I don't get how this is related to patch 3/3 exactly.
> That one seems to clamp the allocations from ewma to at most
> PAGE_SIZE, so how to we get higher-order allocations here?
> Could you clarify please?

If your ewma stabilizes at 2050 bytes per frag, using order-0 page will
waste ~50% of memory.



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