Re: phk malloc, was (Re: ptmalloc2)
You just can't equate the two situations. Trying to compare a system
with overcommit turned on (either physical or swap-backed) with a system
with overcommit turned off is like comparing apples with oranges.
Ignoring the fact that it is past ridiculous to worry about running a
modern system out of swap when you have a 160GB hard drive sitting
there, even the physical memory argument falls on its face because,
quite simply, you cannot have it both ways.
You can't run a system at 100% capacity with overcommit turned off,
it just won't work. You might be able to run it at 25% capacity
100% of the time with overcommit turned off. You could run it at
50% capacity and have occassional memory denials and then pray that
the mostly untested code paths to deal with those denials in the
software work properly. Similarly, you can't run a system at 100%
capacity 100% of the time with overcommit turned on, there will be
load spikes that will drop the efficiency so you will get something
like 100% capacity 99.9% of the time and 80% capacity 0.1% of the time.
But, honestly, if someone came up to me and told me that they were
going to run the system at 25% capacity in order to avoid the
occassional load spike dropping efficiency down, I would fire them on
the spot. And that is crux of the problem here... it is past ridiculous
not to make full use of a system's capacity if you have need of that
capacity. Past ridiculous, which is why the whole argument is totally
and completely bogus and has been bogus for many years now. One wonders
where people get these ideas, it's so nutty. I mean, give me a break,
given the choice between the OS randomly returning a memory allocation
failure and a program self-regulating itself to a particular footprint
size, it's obvious that the only reliable solution is for the program
to self regulate itself, because that is a far more controllable
environment then the OS returning random memory allocation failures.
It's so obvious that it amazes me people still try to make these
ridiculous pie-in-the-sky-software-written-perfectly arguments to
justify turning off overcommit to fix a one in a million year chance
of a properly configured system running out of swap. Past ridiculous.
-Matt
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