Re: Why don't shared anonymous mappings work?

Stephen C. Tweedie
1999-01-13T20:21:19Z

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