From: Florian Weimer <fw@deneb.enyo.de>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: martin capitanio <m@capitanio.org>, linux-kernel@vger.kernel.org,
        torvalds@linux-foundation.org
Subject: Re: mmap, the language go, problems with the linux kernel
References: <1297168678.2190.21.camel@marvin>
	<20110208132657.1cf55782@lxorguk.ukuu.org.uk>
Date: Sat, 12 Feb 2011 15:28:37 +0100
In-Reply-To: <20110208132657.1cf55782@lxorguk.ukuu.org.uk> (Alan Cox's message
	of "Tue, 8 Feb 2011 13:26:57 +0000")
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* Alan Cox:

> Linux implements virtual address space limits, and enforces them. The go
> language stuff wants to allocate huge amounts of virtual space so you
> need to tell the OS you want to allow it to do crazy stuff, which you can
> do so. But virtual address space is not free - it has to be tracked and
> if the application suddenely tries to fill all of it what will happen ?
>
> You'll hit problems if the kernel is running with vm overcommit disabled
> (as well configured servers do),

The odd thing is that prot==0 does *not* count against the
vm.overcommit_memory=2 limit, only against ulimit -v.  The limit is
only enforced for the parts on which mprotect is called.  I think this
should really be part of the public API (I'm not sure if it is right
now, it could well be an accident), to avoid the problems you
describe.
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