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Re: [OCLUG-Tech] Machine becomes unresponsive when allocated large amounts of memory

  • Subject: Re: [OCLUG-Tech] Machine becomes unresponsive when allocated large amounts of memory
  • From: Robert Brockway <rbrockway [ at ] opentrend [ dot ] net>
  • Date: Tue, 14 Feb 2006 02:12:24 -0500 (EST)
On Tue, 14 Feb 2006, Robert Brockway wrote:

On Sun, 12 Feb 2006, tiller man wrote:

The amount of memory I am allocating is almost certainly larger than the amount of physical memory that the machine has available. Not being a linux expert, I assumed that the machine would be able to handle this fairly gracefully through virtual memory allocation. But it doesn't.

There has been long debate over how to handle this condition. The end result has been a configurable solution! :)

I need to clarify this a little. The condition that vm.overcommit_memory deals with is what happens when you try to commit more memory than is available within the entire system (real memory & swap).

If you are just allocating more memory to the app than physical memory then chances are you are just thrashing as others have suggested. Thrashing has to be fairly bad to bring the system to its knees entirely. Different 2.4 kernels dealt with this condition with varying degrees of success.

The difference between thrashing and overcommitting is often easy to detect. If the harddrive light goes on and the disk appears to be very active chances are that you are thrashing. If you overcommit the virtual memory the system might just seem to "fade away". These are not hard and fast rules however.

I hope that makes it a bit clearer.


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