Messages in this thread | | | Subject | Re: A true story of a crash. | Date | Sun, 16 Aug 1998 20:12:11 +0200 (MEST) | From | (, Rogier Wolff) |
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linker@z.ml.org wrote: > > In linux when a process allocates say a meg of memory, the kernel gives it > 256k pages of Copy on write zero page mappings. > > When the process actually writes to these pages, the kernel actually > allcates the memory. This gives increadble performance and memory saving > benifits.. The problem is that you can have 50 apps open and be WAY over > commited.. Then you run out of memory and process (who are not trying any > more allocations are are simply using the ram they allocated at start) > start dieing as they use those COW pages.
Well, this overcommitment is fine in some cases, and not in others. A kernel option that enables the no overcommit case would be nice for some people.
The argument FOR overcommitting memory is:
Almost nobody check the malloc return values. And if they do, all they do is bomb out with "out of memory". If you keep such a process, it might even run to completion.
The argument AGAINST overcommitting is:
I happent to have a couple of important applications that DO know what to do in the "malloc-returns-NULL" case.
Regards,
Roger.
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