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Old 03-15-2013, 11:46 AM   #1
VisionIncision
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Obtaining memory access information


Hi all,
I have an idea for a project, a very cool project. Is there any way to obtain detailed memory access information for a given process or set of processes. I would need to encode the data for use in Machine Learning algorithms, particularly those pertaining to Artificial Neural Networks.

Thanks,
Jack Hunt
 
Old 03-15-2013, 12:56 PM   #2
sunnydrake
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gdb, /proc/"pid"
 
Old 03-15-2013, 01:06 PM   #3
jpollard
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The usual problem is "it depends".

It depends on what you mean by "memory access information".

Basic paging statistics are available...

The usual problem with trying to use them is that the information is too coarse for any real use other than crudely optimizing the paging algorithm.

One example of a problem of insufficient data has to do with identifying if a page has been modified. To do it right requires hardware. HOWEVER, it can be done by software - by making all pages read only... if a write fault occurs, AND the OS has designated the page to be writable, then the page is made r/w, and the OS data marks it as "dirty"... then the interrupt is dismissed, and the instruction retried.

Slow... but workable. Use for statistics? really bad. frequently you would like to know "how often" is a page written to, how long between writes... to get that detailed amount of information really really needs hardware.
The next problem is that if you actually get enough information for good use, it comes way too fast (such as a program counter trace) for any use. Computing a modified paging algorithm takes longer than it takes the application being traced to run...

Most that I've met take a paging statistics snapshot once every 5-10 seconds, then spends a half second to compute updates...

Last edited by jpollard; 03-15-2013 at 01:14 PM. Reason: small followup.
 
Old 03-16-2013, 02:54 AM   #4
sunnydrake
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another approach is to gather executable/loaded opcodes memory access instructions statistics/modify executable to add statistics info before memory access..
 
Old 03-16-2013, 09:13 AM   #5
ntubski
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Valgrind might be useful for this:
Quote:
Valgrind is an instrumentation framework for building dynamic analysis tools.
Memcheck is one of the tools that comes with Valgrind:
Quote:
When a program is run under Memcheck's supervision, all reads and writes of memory are checked, and calls to malloc/new/free/delete are intercepted.
...
Memcheck runs programs about 10--30x slower than normal.
 
Old 03-18-2013, 04:13 PM   #6
VisionIncision
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Ah ok, looks as if I wont be able to do what I need to do. Thanks guys.
 
  


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