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SubjectRe: Overcomittable memory
Date
On Tue, 21 Mar 2000 12:20:30 +0000, you wrote:

>James Sutherland wrote:
>> On Mon, 20 Mar 2000 19:12:13 -0800 (PST), you wrote:
>> >On Mon, 20 Mar 2000, James Sutherland wrote:
>> >>On Mon, 20 Mar 2000 19:04:06 +0000, you wrote:
>[...]
>> >Currently there is no way to disable overcommit in Linux.
>>
>> True; to disable it completely, you would need to remove the dynamic
>> stack expansion, giving every process a fixed-size stack. Another Gb
>> or so of wasted swap, another few unexplained crashes...
>
>Where are you getting this from? The whole point of that nice example I
>gave previously was that there were no reasons whatsoever that it could
>die. None at all. Zip. Nadda. Please find one.

Whenever you use the stack, unless you were providing your own,
fixed-size stack.

>Not to mention the program would be actively using the entire of its
>allocated memory, so swap isn't exactly wasted.

If your process is actively using the space, it will never be affected
by overcommit anyway.

> In fact, you now know
>exactly how much memory+swap you need. In the example, it used 512MB. So
>you'd need exactly (give or take a few pages) 512MB more RAM or swap
>(preferably RAM). This would be exactly the same amount you'd need if
>you ran it with overcommit turned on.

So overcommit doesn't cause any possible problems.

>The important difference is that other processes will not cause the big
>512MB process to die. This is the behaviour I've been trying to
>describe.

This has nothing to do withovercommit. Your process may be killed for
a variety of reasons (system low on resources, hostile sysadmin,
system reboot, etc.) but nothing to do with overcommit.

This is true whether overcommit is enabled or not.


James.

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