Re: execve(NULL, argv, envp) for nommu?

From	Alan Cox <gnomes@lxorguk.ukuu.org.uk>
Newsgroups	linux.kernel
Subject	Re: execve(NULL, argv, envp) for nommu?
Date	2017-09-11 20:20 +0200
Message-ID	<uoBto-6V3-7@gated-at.bofh.it> (permalink)
References	<umi1P-Ly-7@gated-at.bofh.it> <umi1P-Ly-5@gated-at.bofh.it> <umm5r-38R-5@gated-at.bofh.it> <umxay-2mO-5@gated-at.bofh.it>
Organization	Intel Corporation

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> It's not the performance cost, it's rewriting all the pointers.

Which you don't need to do

> Without address translation, copying the existing mappings to a new
> range requires finding and adjusting every pointer to the old data,

No it doesn't. See Minix.

When you fork() rather than vfork you stick a copy of any non-relocatable
elements (typically DATA copy + BSS + stack with a sane CPU and compiler)
into a buffer and you swap them over with the real copy when you task
switch to the one in the wrong place. If you start the child first you
usually only take one copy.

I've always been amused that Linux NOMMU hasn't managed to grow a feature
that people successfully implemented on 68000 long long ago, and I
believe some other processors back to v6/v7 days.

Alan

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Re: execve(NULL, argv, envp) for nommu? Geert Uytterhoeven <geert@linux-m68k.org> - 2017-09-05 11:10 +0200
  Re: execve(NULL, argv, envp) for nommu? Alan Cox <gnomes@lxorguk.ukuu.org.uk> - 2017-09-05 15:30 +0200
    Re: execve(NULL, argv, envp) for nommu? Rob Landley <rob@landley.net> - 2017-09-06 03:20 +0200
      Re: execve(NULL, argv, envp) for nommu? Rob Landley <rob@landley.net> - 2017-09-08 23:20 +0200
        Re: execve(NULL, argv, envp) for nommu? Oleg Nesterov <oleg@redhat.com> - 2017-09-11 17:20 +0200
          Re: execve(NULL, argv, envp) for nommu? Rob Landley <rob@landley.net> - 2017-09-12 12:50 +0200
            Re: execve(NULL, argv, envp) for nommu? Geert Uytterhoeven <geert@linux-m68k.org> - 2017-09-12 13:40 +0200
              Re: execve(NULL, argv, envp) for nommu? Rob Landley <rob@landley.net> - 2017-09-12 15:50 +0200
                Re: execve(NULL, argv, envp) for nommu? Alan Cox <gnomes@lxorguk.ukuu.org.uk> - 2017-09-13 21:40 +0200
            Re: execve(NULL, argv, envp) for nommu? Oleg Nesterov <oleg@redhat.com> - 2017-09-12 17:50 +0200
              Re: execve(NULL, argv, envp) for nommu? Oleg Nesterov <oleg@redhat.com> - 2017-09-13 16:30 +0200
      Re: execve(NULL, argv, envp) for nommu? Alan Cox <gnomes@lxorguk.ukuu.org.uk> - 2017-09-11 20:20 +0200

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