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Re: Memory management by 5.4 on Sunblade [message #28593 is a reply to message #28436]

Thu, 20 December 2001 08:51

John-David T. Smith is currently offline

John-David T. Smith
Messages: 384
Registered: January 2000

Senior Member

Craig Markwardt wrote:
>
> JD Smith <jdsmith@astro.cornell.edu> writes:
>> Timm Weitkamp wrote:
>>>
>>> Hi,
>>>
>>> I'm mostly using IDL 5.4 on my laboratory's Linux86 cluster, and
>>> running memory-critical simulation code on it which uses lots of large
>>> temporary arrays.
>>>
> ...
>>> However, I noticed that memory management by IDL 5.4 on the Sunblade
>>> is extremely poor in that variable space "freed" by TEMPORARY, DELVAR,
>>> or simply by dynamic resizing of a variable is not actually freed but
>>> kept allocated (so tells me "top").
> ...
>>
>> It's not a *bug*, it's a *feature*. IDL allocates memory as necessary
>> from the OS, and then, even if it doesn't need it any more, hangs onto
>> it just in case. This is true I think on all platforms, and all recent
>> versions of IDL. You still have the memory available, just not to the
>> system as a whole.
>
> Hi JD--
>
> I do not think this is always true. I find that I regularly create
> 300 MB arrays in memory, and then free them. While the procedure is
> running, the memory usage is indeed around 300 MB, but afterwards the
> memory use, as reported by the external program "top", drops down
> again to the quiescent level.
>

Two strikes this week. Maybe I should stick to histograms. Indeed, so
much has this mis-feature been touted, that I presumed it applied
everywhere. Testing on my linux system reveals Craig to be entirely
correct: even as far back as v5.2.1, memory is released to the OS after
it's not needed. Yet another reason to avoid Solaris, I suppose.

Here's a fun command to use to track memory usage:

% watch -n 1 'free;echo;ps -C idl -o rss,vsize,cmd'

JD

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[Message index]

		Memory management by 5.4 on Sunblade By: weitkamp on Mon, 17 December 2001 02:57
		Re: Memory management by 5.4 on Sunblade By: John-David T. Smith on Wed, 19 December 2001 14:41
		Re: Memory management by 5.4 on Sunblade By: John-David T. Smith on Thu, 20 December 2001 10:50
		Re: Memory management by 5.4 on Sunblade By: Craig Markwardt on Wed, 19 December 2001 21:50
		Re: Memory management by 5.4 on Sunblade By: David Fanning on Thu, 20 December 2001 08:57
		Re: Memory management by 5.4 on Sunblade By: John-David T. Smith on Thu, 20 December 2001 08:51
		Re: Memory management by 5.4 on Sunblade By: weitkamp on Thu, 20 December 2001 02:36
		Re: Memory management by 5.4 on Sunblade By: Nigel Wade on Thu, 20 December 2001 01:45

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