Re: Why don't shared anonymous mappings work?

["Stephen C. Tweedie" <sct@redhat.com>]

Hi,

On 06 Jan 1999 23:55:03 -0600, ebiederm+eric@ccr.net (Eric W. Biederman)
said:

> And of course the last reason I just thought of, which is probably the
> real reason.  Currenlty anonymous pages if the are writable are
> assumed to have exactly one mapping, or if it is in the swap cache the
> page is assumed to be read only.

> So reusing the swap inode could be a real problem.

Yes.  The _only_ reason we can't do anonymous pages right now is the
VM's assumption that all swap cache pages are read-only.  Once we relax
that, the only thing left is the initialisation of anonymous page ptes
(remembering that when we fill in a demand-zero anonymous shared page,
we will have to update that page's pte in every mm which shares the
page).  Other than that, allowing writable swap-cache pages is all that
is required.  It's just too much of a potential destabiliser to add this
close to 2.2.0.

--Stephen

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