Re: [PATCH -mm] Revoke core code: fix nommu arch compiling error bug

Andrew Morton
2007-03-26T11:50:58Z

On Mon, 26 Mar 2007 12:25:18 +0100 David Howells <dhowells@redhat.com> wrote:

> Andrew Morton <akpm@linux-foundation.org> wrote:
>
> > Offending patch is
> > ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.21-rc4/2.6.21-rc4-mm1/broken-out/nommu-hide-vm_mm-in-nommu-mode.patch,
> > which seems rather dumb. Or at least, its changelog does a good job of
> > making it look dumb.
>
> vm_mm is always NULL under NOMMU as it currently stands. As far as I know,
> this has been true since the NOMMU mm stuff was first included (I'm not sure
> the VMAs of the first NOMMU mm code *had* a vm_mm). Hugh (I think it was)
> suggested that since this was always NULL, then it should be excised from the
> struct in NOMMU-mode.
>
> The reason is that, at the moment, VMAs are a global *shared* resource in
> NOMMU-mode. Each process has a list of global VMAs that it subscribes to, but
> that's it. This (a) slightly reduces the amount of metadata allocated
> (possibly), and (b) makes sharing of executables and libraries much easier.

whoa. You live and learn. Logical, I guess.

I agree that in that case, we just don't want vm_mm to exist in NOMMU builds - it's
better to fail at compile time.

I'll touch up the changelog for nommu-hide-vm_mm-in-nommu-mode.patch and then
I'll temporarily drop it so the blackfin guys can test their work, I guess.