netdev - Re: [PATCH net-next 2/3] virtio-net: use per-receive queue page frag alloc for mergeable bufs

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Date:	Thu, 26 Dec 2013 23:37:27 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Michael Dalton <mwdalton@...gle.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Jason Wang <jasowang@...hat.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Eric Dumazet <edumazet@...gle.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	lf-virt <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH net-next 2/3] virtio-net: use per-receive queue page frag
 alloc for mergeable bufs

On Thu, Dec 26, 2013 at 01:28:58PM -0800, Michael Dalton wrote:
> On Mon, Dec 23, 2013 at 11:37 AM, Michael S. Tsirkin <mst@...hat.com> wrote:
> > So there isn't a conflict with respect to locking.
> >
> > Is it problematic to use same page_frag with both GFP_ATOMIC and with
> > GFP_KERNEL? If yes why?
> 
> I believe it is safe to use the same page_frag and I will send out a
> followup patchset using just the per-receive page_frags.

Seems easier to use it straight away I think.

> For future
> consideration, Eric noted that disabling NAPI before GFP_KERNEL
> allocs can potentially inhibit virtio-net network processing for some
> time (e.g., during a blocking memory allocation or preemption).
> 
> Best,
> 
> Mike

Interesting. But if we can't allocate a buffer how can we
do network processing?

If we can reproduce the problem, we can maybe move
allocation out of napi disabled section, but then
we'll need to add more locking.

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