X Server: abused or buggy?

Óscar Fuentes ofv at wanadoo.es
Tue Dec 9 10:15:26 PST 2008

Glynn Clements <glynn at gclements.plus.com> writes:

>> So in your opinion using X as a cache for 500 MB of pixmaps is dumb. I
>> tend to agree, but it is reasonable to expect that when the app closes
>> and the pixmaps are freed, all that memory is returned to the OS?
> Not really. Most applications just use malloc() and free(), or
> something similar.

In this case, the X server does not qualify as an ordinary
application. It provides services to other applications and should do so
without degrading the quality of the whole system. See below.


>> In other words, is a bug that under this usage mode the memory
>> asigned to X grows monotonically?
> No. Most long-lived applications have memory "usage" which grows
> monotonically, for the reasons outlined above. I put "usage" in quotes
> because they won't necessarily be *using* the memory; they'll just
> have it allocated (and swapped out).

It is my impression that Okular's maintainers think that the X server is
providing a service that their application is using. If this causes an
steadily resource degradation, it's a bug on the service provider. IMO
this point of view makes sense, if and only if using the X server for
massively caching large pixmaps enters within the expected uses of the
service. Even if this is considered abusing the X server, retaining
large portions of memory after the serviced app closes reveals a poor
QoI. Okular's maintainer expected that if heap fragmentantion could
happen for resources stored on the X server, it should perform some sort
of memory compaction for avoiding it. He architectured the app to
exploit the X server caching feature and refuses to consider any other
option, arguing that is the X server who needs to be fixed.


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