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< Advanced Erlang/OTP ~ Massive virtual size and acceptable resident size |
| kjkoster |
 Posted: Wed Dec 23, 2009 9:49 pm |
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Joined: 23 Dec 2009
Posts: 2
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Dear All,
We're running with a decently-sized ejabberd setup. Under load, the ejabberd process grows to about 5GB resident size (according to Linux top), which is fine. We have 8GB in the machine, so no worries.
However, top also shows the process to have about 25-30GB of virtual size. This is an issue, because once the machine reaches a virtual allocation size of about 40GB it locks up and need a hard reset to bring to live again.
Interestingly, the machine does not swap at all. It never seems to actually touch most of the virtual memory allocated to the process, otherwise these pages would have to be stored in swap.
From my understanding this means that the Erlang process is allocating a lot more memory than it actually uses. Can anyone confirm or deny this?
How can I see where that memory is being allocated? Is there a way to make the Erlang runtime not allocate memory it is not actually touching?
Kees Jan |
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| uwiger |
| Posted: Thu Dec 24, 2009 8:07 pm |
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Joined: 03 Jul 2006
Posts: 604
Location: Sweden
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kjkoster wrote:
However, top also shows the process to have about 25-30GB of virtual size. This is an issue, because once the machine reaches a virtual allocation size of about 40GB it locks up and need a hard reset to bring to live again.
I think that in general it's ok to let Erlang use some swap, but if you have 5 times more memory in swap than resident in RAM, I'd say all bets are off. Erlang doesn't do any caching on its own, so it basically assumes that all data is resident. Remember that Erlang was designed for soft real-time.
Perhaps someone else has a different experience.
BR,
Ulf W |
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| kjkoster |
| Posted: Fri Dec 25, 2009 10:03 am |
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Joined: 23 Dec 2009
Posts: 2
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Dear Ulf,
That's the strange thing: it uses no swap at all. It allocates the 20GB virtual memory and then works happily in something like 5GB without ever touching swap.
So in top the VIRT column reads "20GB", the RES column reads "5GB" and the swap-in-use field reads 0.
Why does Erlang allocate the excess 15GB?
Kees Jan |
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| wuji |
| Posted: Tue Sep 18, 2012 6:12 am |
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