I'm currently trying to port DateTime::TimeZone to XS so that it consumes less memory. But I'm currently being baffled by the seeming *increase* in the memory being used by loading the XS version of the module.

DateTime::TimeZone is comprised of a a base class, DateTime::TimeZone, and a few hundred subclasses which represent each time zone. For example, Asia/Tokyo timezone is represented as DateTime::TimeZone::Asia::Tokyo. Each of these timezones contains a list of data, which I've now converted to C structs.

Now, loading one time zone and comparing its size with what Devel::Size reports, the savings are clear. Here's an example:

   Europe/Belfast: 51735 (Pure Perl)
   Europe/Belfast: 2525 (XS)

[download]

However, this isn't translating into actual memory savings. This is the output from my top (Mac OS X)

     PID COMMAND      %CPU   TIME   #TH #PRTS #MREGS RPRVT  RSHRD  RSI
+ZE  VSIZE
(XS) 26873 perl         0.0%  0:03.43   1    12  1177  14.6M  12.0M  2
+1.9M  51.0M 
(PP) 26872 perl         0.0%  0:02.83   1    12    46  13.4M  1.42M  1
+4.6M  33.3M

[download]

What gives? The XS version seems to consume more than 18 MB more than the pure perl version?! I think I've applied all the XS hackery I know to reduce memory consumption, is there any tips to reduce this memory size? or am I looking at the wrong numbers?

In reply to memory penalty for loading XS modules? by lestrrat

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