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Is your memory fragmented? What can you do about it? 3

Posted by Brett Shoelson,

Want to know? Then download Stuart McGarrity's CHKMEM submission!

Brett's Pick this week helps you determine if your memory is fragmented, and, more importantly, what steps you might take to minimize 'Out of Memory' errors. Many of you know of Stuart from the MATLAB Central File Exchange; for years, when we tracked these things, he was the most-downloaded author on the Exchange. Those of us who know him as a colleague at The MathWorks know him as well as a guru of sorts for dealing with memory (and out-of-memory) issues.

Suppose you wanted to know the size of the largest variable you could create at any given moment in MATLAB. We know from the documentation for the MEMORY command that the largest possible variable is the smaller of the following two values: a)The largest contiguous memory block found in the MATLAB virtual address space, and b) The total available system memory. (The MEMORY command will return this value in a field called MaxPossibleArrayBytes.) Stuart's file CHKMEM takes MATLAB's memory command and does it one better. CHKMEM compares the largest available variable size to your system's RAM and provides suggestions for decreasing the gap between the two. It also suggests ways to increase the available physical memory. For instance, I had thought that my 3-GB switch was enabled; Stuart's code informed me that, in fact, it is not currently set. And then he provides links to documentation showing how to set it!

Very nice utility, Stuart! Thanks for sharing it.

Comments? Share them here.

Get the MATLAB code

Published with MATLAB® 7.8


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3 CommentsOldest to Newest

us replied on : 1 of 3
hi brett! and thanks for alluding to stuart's great submission... in addition to this utility, i'd like to alert the wintel system users to a recent piece from windows sysinternal: VMMAP (1.1), available here which does an amazing job in giving you all the information you ever wanted (re memory issues)... best urs
Yair Altman replied on : 2 of 3
Thanks for spotlighting this useful utility Brett. Chkmem uses two of Matlab's standard memory-reporting utilities. But except for making the data human-readable, Chckmem adds its own processing, suggesting specific remedies for specific issues detected, along with some external links. This causes Chkmem to have a big added value over using Matlab's basic functions, and is a great example of extending Matlab's basic functionality with external resources. However, users should note that Chkmem relies on undocumented features (feature 'memstats' and 'dumpmem') which are unsupported by MathWorks and might break without prior warning in a future release. I personally have no problem with this, but it should be noted for the record. users interested in these undocumented memory features may also be interested in checking the output of the related feature('processmem'), which is not used by Chkmem. Yair
Brett replied on : 3 of 3
Urs and Yair, Thanks for your helpful comments. Urs-I haven't yet tried it, but VMMap _looks_ like a very useful additional utility. By the way, I should also have pointed out that Stuart's CHKMEM only works on 32-bit Windows systems. VMMAP, too, is Windows-centric (it's from Microsoft), and is, I believe, compatible with 64-bit systems. However, Google turns up some discussions about problems with using it on 64-bit machines. And Yair, thanks, too, for pointing out that Stuart's submission uses undocumented functionality. I should have pointed that out myself. We've struggled in the past with whether or not to steer away from featuring submissions that use undocumented commands. Sometimes they're just too good to pass up! (Some of your own files fall in that category, by the way.) Cheers, Brett