Date: Thu, 16 Sep 2004 19:45:30 +0200
From: Arjan van de Ven <arjanv@redhat.com>
To: Utz Lehmann <lkml@de.tecosim.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] flexmmap: optimise mmap_base gap for hard limited stack
Message-ID: <20040916174529.GA16439@devserv.devel.redhat.com>
References: <20040916165613.GA10825@de.tecosim.com>
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On Thu, Sep 16, 2004 at 06:56:13PM +0200, Utz Lehmann wrote:
> Hi
> 
> With the flexmmap memory layout there is at least a 128 MB gap between
> mmap_base and TASK_SIZE. I think this is for the case that a running process
> can expand it's stack soft rlimit.
> 
> If there is a hard limit for the stack this minium gap is just a waste of
> space. This patch reduce the gap to the hard limit + 1 MB hole. If a process
> has a 8192 KB hard limit it have additional 119 MB space available over the
> current behavior.


I'm not so convinced this is the right approach... a bit of room for the
apps to increase their stack sounds useful. (and a "reasonable" amount is
SuS specified afaik, 128Mb is quite reasonable)

 
> And the current implemention has a problem. If the stack soft limit is
> 128+ MB there is no hole between the stack and mmap_base. If there is a
> mapping at mmap_base stack overflows are not detected. The patch made a
> 1MB hole between them.

ack on this part.

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