netdev - Re: [PATCH net] virtio-net: fix page refcnt leaking when fail to allocate frag skb

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Date:	Tue, 19 Nov 2013 14:00:11 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Jason Wang <jasowang@...hat.com>, rusty@...tcorp.com.au,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Michael Dalton <mwdalton@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net] virtio-net: fix page refcnt leaking when fail to
 allocate frag skb

On Tue, 2013-11-19 at 23:53 +0200, Michael S. Tsirkin wrote:

> Which NIC? Virtio? Prior to 2613af0ed18a11d5c566a81f9a6510b73180660a
> it didn't drop packets received from host as far as I can tell.
> virtio is more like a pipe than a real NIC in this respect.

Prior/after to this patch, you were not posting buffers, so if packets
were received on a physical NIC, you were dropping the packets anyway.

It makes no difference at all, adding a cushion might make you feel
better, but its really not worth it.

Under memory stress, it makes better sense to drop a super big GRO
packet (The one needing frag_list extension ...)

It gives a better signal to the sender to reduce its pressure, and gives
opportunity to free more of your memory.



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