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SubjectRe: Overcommitable memory??
Den 14-Mar-00 18:32:49 skrev Rik van Riel følgende om "Re: Overcommitable memory??":
> On 13 Mar 2000, Rask Ingemann Lambertsen wrote:

[program crash because demand loading fails due to no memory]
>> Without overcommit that just can not happen. There will be
>> either a free page of memory or a free page of swap into which
>> you can swap something else out.

> Without overcommit it can still happen, unless you reserve one
> page of swap space for every page of data that gets mmap()ed...

Not having swap or RAM for every page of mmap()ed data means that you
are overcommitting memory. If you're mmap()ing a file, then that file can
count as swap too. Files with "holes" in them may be a problem.

>> Please realize that the only gain from overcomitting memory
>> is that yoy may get away with having less swap space. The
>> downside you get is random program crashes, lost work, etc.

> Not really. Without overcommit you may still have random program
> crashes and lost work...

Yes, really. Maybe I should have said "additional lost work" instead of
just "lost work". Without overcommit, program crashes will only happen due
software bugs or hardware problems. Lost work will only happen due to user
errors, software bugs or hardware problems. If you overcommit memory, you
can lose the file you were editing in emacs simply because someone sent you
an email and the MTA needed a bit of memory to deliver it to you. Some
people, myself included, just don't find that acceptable at all.

Regards,

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| Rask Ingemann Lambertsen | E-mail: mailto:rask@kampsax.dtu.dk |
| Please do NOT Cc: to me or the | WWW: http://www.gbar.dtu.dk/~c948374/ |
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