On Thu, 16 Mar 2000, James Sutherland wrote:
> No. *ANY* memory allocation system can run out of memory. Avoiding
> "overcommitting" would make the OOM situation arise SOONER (and more
> frequently), as well as killing performance.
>
well, it's a more a question of whether you make promises that you might
not be able to keep. If you do (ie overcommit) then it's your
(kernel) problem. If you don't, it's not.
Without overcommit the /system/ can run out memory, of course - it's
finite - but it's no longer a kernel problem.
> Right... Now we'll try this on the university's central Unix system, shall
> we? Let's see... 6000 users, 2Gb RAM+swap. They get about 300K each.
> That's ALMOST enough to log in with!
well then get more ram/swap. But at least it has become a hw issue.
> The alternative just isn't practical in any real-world situation, except
> more-or-less single user boxes.
the alternative is very practical. boxes where oracle runs as one user /
apache as another for example. You might want to lock down something
that you know can cause problems.. etc..
> Even then, that single user will still run
> out of memory - it's just his quota, rather than a physical limit.
>
obviously.
> So his processes STILL end up dying randomly, but they do it sooner rather
> than later. Hrm. Wow.
>
but then it's the users problem - not the OS..
> On any realistically specced box, it is almost zero already.
>
no it's not. a plain linux box today has a terrible tendency to die if
an app misbehaves wrt to memory. It's that bad. (unless you think 1GB of
RAM + 4GB's+ of swap is a reasonable spec for a desktop)
per process limits go a long long way to solving this (easy with
pam_limits) but not far enough. But per user limits would be a huge
improvement...
> No, it's a risk with *EVERY* OS.
no it's not. A non overcommiting OS doesn't run out of VM for
processes. it cleanly grants or denies memory requests. What the app
does after that is not a kernel problem.
>
> James.
>
-paul jakma
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