On Mon, Sep 19, 2016 at 12:13 PM, Jeroen Demeyer <jdeme...@cage.ugent.be>
wrote:

> On 2016-09-19 13:02, Jonathan Bober wrote:
>
>> If I ulimit -v 8 GB, say, (which is 512/64), and the PARI allocater
>> immediately grabs 2 GB of the virtual address space for itself, then
>> that seems like it leaves only 6 GB for malloc/sage_malloc/whatever
>> else, which would be effectively limiting the physical memory available
>> in some situations.
>>
>
> Then use a larger value for "ulimit -v" or add some swap space.
>
>
That doesn't really solve the problem, which I phrased poorly. The machine
has an (antiquated) setup where, when a process requests X bytes of memory,
the kernel reserves X bytes of physical memory for it. This is usually fine
because users usually use the memory they request, and when they don't,
well, there are 512 GB of it. But it does mean that every virtual memory
allocation has a physical memory cost. (It also has benefits, like when
someone screws up they usually notice immediately, instead of when the OOM
killer kills sshd or the login process.)


> This is not the default, and you probably wouldn't want to
>> run your laptop this way
>>
>
> But it is an advanced setting. Given that, I assume that you are clever
> enough to do the right thing.


With overcommit_memory set to 2, I'm not sure that there is a right thing
to do. If I'm the only person in the world with this problem, then I should
keep my mouth shut and get with the times, but I don't think this setup is
so unreasonable.

Anyway, where exactly is this allocation coming from? Is it a default PARI
setting, or does it come from the way that Sage uses PARI? (I mean, to whom
should I address my "hate mail"? :)


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