From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <01b719eaabe004a9073ccb4b3425e1d0@plan9.bell-labs.com>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] plan 9 overcommits memory?
Date: Sun,  2 Sep 2007 23:38:44 -0400
From: geoff@plan9.bell-labs.com
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If system calls were the only way to change memory allocation, one
could probably keep a strict accounting of pages allocated and fail
system calls that require more VM than is available.  But neither Plan
9 nor Unix works that way.  The big exception is stack growth.  The
kernel automatically extends a process's stack segment as needed.  On
the pc, Plan 9 currently limits user-mode stacks to 16MB.  On a CPU
server with 200 processes (fairly typical), that's 3.2GB of VM one
would have to commit just for stacks.  With 2,000 processes, that
would rise to 32GB just for stacks.