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Date: Mon, 25 May 2015 11:51:23 +0800
From: Fam Zheng <famz@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v3 04/13] netmap: Drop netmap_can_send
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org, Juan Quintela <quintela@redhat.com>, Jason Wang <jasowang@redhat.com>, qemu-devel@nongnu.org, Vincenzo Maffione <v.maffione@gmail.com>, "Vassili Karpov (malc)" <av1474@comtv.ru>, Gerd Hoffmann <kraxel@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, Amit Shah <amit.shah@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Giuseppe Lettieri <g.lettieri@iet.unipi.it>, Luigi Rizzo <rizzo@iet.unipi.it>

On Tue, 05/19 15:54, Stefan Hajnoczi wrote:
> On Tue, May 19, 2015 at 10:51:01AM +0000, Fam Zheng wrote:
> > This callback is called by main loop before polling s->fd, if it returns
> > false, the fd will not be polled in this iteration.
> > 
> > This is redundant with checks inside read callback. After this patch,
> > the data will be copied from s->fd to s->iov when it arrives. If the
> > device can't receive, it will be queued to incoming_queue, and when the
> > device status changes, this queue will be flushed.
> > 
> > Also remove the qemu_can_send_packet() check in netmap_send. If it's
> > true, we are good; if it's false, the qemu_sendv_packet_async would
> > return 0 and read poll will be disabled until netmap_send_completed is
> > called.
> 
> This causes unbounded memory usage in QEMU because
> qemu_net_queue_append_iov() does not drop packets when sent_cb != NULL.

I think netmap_send will use "netmap_read_poll(s, false)" to stop reading, only
the first packet will be queued. Why is it unbounded?

Fam