How to disable/limit pixmap cache in X

Jim Kronebusch jim at
Wed Sep 19 17:31:07 PDT 2007

> I had assumed that Jim was under the impression that the server was
> merely "caching" this data as an optimisation, and that reducing the
> amount of memory used would merely degrade performance. That isn't the
> case.

Yes, I was under the impression that this was for optimisation.  I understand now that
the application may be using it as an optimisation but for X this is not the case and
refusal to accept pixmaps could cause the application to crash (I hope what I just
stated is accurate).  But the fact still remains that an application can abuse pixmap
storage (such as firefox) and without the server having some sort of limits in place
this is able to crash the client.  So to me there should be some mechanism in place that
does not allow this to happen.  I was hoping there was an easy or at least only
moderately difficult way to make this happen....apparently not.  I was hoping there was
a way to put a size limit specifically on pixmap storage and refuse any requests from an
application beyond that point.  I had hoped that this would cause the application to
simply move on or not request pixmap storage and not cause the application to crash. 
But since that seems to only be controlled on the application side rejection will
ultimately cause the application to crash.  This of course isn't ideal, but crashing the
offending application is still way better than crashing the server and freezing the
client and allowing a user to still continue working in other applications.

To me this seems to be the only sensible way for the server to react.  I wouldn't think
there would ever be any circumstance where you would want to allow the
client/application to crash the server.

Am I making any sense here?  I'll admit I don't really know much of anything about how X
works, and as a result I have no real knowledge on how this should be fixed.  All I do
know is this is a huge problem that seems to be rapidly getting worse and is causing
sever instability in remote X usage such as Linux thin clients or in lower memory machines.

So consider this a desperate plea for help.


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