Re: [Qemu-devel] [PATCH 2/4] vnc: allow the Buffer to shrink again

[Peter Lieven]

Am 03.09.2015 um 11:52 schrieb Gerd Hoffmann:
> On Do, 2015-08-27 at 11:39 +0100, Daniel P. Berrange wrote:
> > On Thu, Aug 27, 2015 at 12:18:52PM +0200, Peter Lieven wrote:
> > > currently the Buffer can only grow. This increases Qemu memory footprint
> > > dramatically since normally the biggest VNC updates are at connection time.
> > > But also after a VNC session has terminated there is one persistent buffer
> > > in queue->buffer which I have seen to increase to over 100MB and it is never
> > > getting smaller again.
> > Do you have any idea what caused the buffer to increase to 100MB in size
> > in the first place ? I would expect a full screen update would cause the
> > biggest buffer usage, and even for a 1920x1140 screen that should not
> > be anywhere near 100MB in size. IOW, i'm wondering if the 100MB usage
> > is symptomatic of a more serious bug somewhere else in the VNC code
> > that you're just masking you reducing buffer size afterwards.
> Cooked up a buffer stats patch (attached).
> Buffer sizes are nowhere near 100MB for me (as expected by Daniel).
> Individual buffers are in the 1 -> 4 MB range (1920x1080), even summed
> up this is more like 10 not 100 MB.
>
> So, big question remains why they are that big for you?

I will try the patch out. Thank you.

> Beside that I think it makes sense to have the shrinking logic in
> buffer_reserve too so we don't have to add buffer_shrink calls all over
> the place.

We need a possibility to shrink the buffer after it has been used.
Especially the queue->buffer.

Thanks,
Peter