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

[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?

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.

cheers,
  Gerd

0001-debug-vnc-buffer-stats.patch
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