Re: Overcommitable memory??

From: Rask Ingemann Lambertsen (
Date: Sat Mar 18 2000 - 20:09:09 EST

Den 17-Mar-00 00:55:01 skrev James Sutherland fĝlgende om "Re: Overcommitable memory??":

> Yes... So if you disabled overcommit, AND used a malloc wrapper which
> touches every page when it is allocated, you could guarantee the memory
> you had been "allocated" was REALLY allocated.

   When you say "disabled overcommit", are you referring to the current
implementation of /proc/sys/vm/overcommit_memory set to zero? If so, you
are right, except that an OOM killer can still select your process to be
the one to kill. I.e. you could have saved your trouble. Worse yet, you
could cause another process to be killed because you touch the pages.

   If you're talking about a working option to disable overcommitment of
memory, then:

   1. If you don't overcommit, there is no need to touch the pages and no
      gain from doing so.
   2. If you do overcommit, touching the pages won't protect you from an
      OOM killer.

> Anyway, this all has nothing to do with the original topic, which related
> to how to handle out-of-memory situations - i.e. once all the memory has
> been allocated, however you allocate it.

   Only one thing: If you don't overcommit memory, the kernel will never
need to use an OOM killer.


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