core dumps are HUGE...
Chuck Swiger
cswiger at mac.com
Wed Mar 22 14:11:32 UTC 2006
Hi, Jason--
First, thanks for your work on the new jemalloc.
Jason Evans wrote:
> On Mar 21, 2006, at 2:20 PM, John-Mark Gurney wrote:
[ ... ]
>> And yes, I'm pretty sure that I have a world from before your reduction
>> in chunk size... Having a minimum of a 6meg core doesn't sound like a
>> good idea... It's definately not going to play nice with small systems..
>
> I don't think that a 6 MB core file is the big deal you are making it
> out to be. A 50 MB core file is a pain, mainly because it takes a long
> time to dump core.
The smallest processes that people run often are likely going to be /bin/sh and
the typical fodder of shell scripts (grep, awk, and so forth). Under 4.x,
/bin/sh tended to have VSIZE of 640K and RSS of ~300K; under 5.x and later,
/bin/sh has VSIZE of 1.6MB and RSS of ~1MB.
Creating a 50MB corefile from a 2MB VSIZE process is unreasonable. Creating a
6MB corefile from a 2MB VSIZE process would be reasonable but probably could be
improved by a factor of two.
On the other hand, the staticly linked "t" program is:
chuck 62964 0.0 0.1 232 128 p0 TX 8:09AM 0:00.03 /tmp/t
128K RSS, 232 VSIZE. A 6MB corefile is a factor of 25 larger, which strikes me
as something that could be improved by more than a factor of ten.
What else is being dumped that's not counted by VSIZE, aside from a header and
maybe some per-thread state, (although aren't the per-thread stacks already part
of VSIZE)...?
Can jemalloc only create per-CPU arenas only for processes which are themselves
multithreaded, when it's running on a multi-CPU system? Would that help reduce
the amount of allocated but unreferenced memory that is involved for the common
case of /bin/sh and friends?
> Even so, consider that core dumps on OS X are in
> excess of 90 MB, and that this hasn't caused the world to stop revolving
> (though we should blame OS X for global warming).
Dear Cthulhu, you're right.
I was sure this was FUD, and I would have been wrong. :) The one-line test
program from earlier in the thread creates a 147MB coredump under 10.4.5...I
need to file a radar or two with Apple.
--
-Chuck
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