Re: [PATCH 2/4] Add replace_page(), change the mapping of pte from one page into another

[Christoph Lameter <cl@linux-foundation.org>]

On Tue, 11 Nov 2008, Andrea Arcangeli wrote:

> btw, page_migration likely is buggy w.r.t. o_direct too (and now
> unfixable with gup_fast until the 2.4 brlock is added around it or
> similar) if it does the same thing but without any page_mapcount vs
> page_count check.

Details please?

> page_migration does too much for us, so us calling into migrate.c may
> not be ideal. It has to convert a fresh page to a VM page. In KSM we
> don't convert the newpage to be a VM page, we just replace the anon
> page with another page. The new page in the KSM case is not a page
> known by the VM, not in the lru etc...

A VM page as opposed to pages not in the VM? ???

page migration requires the page to be on the LRU. That could be changed
if you have a different means of isolating a page from its page tables.

> The way to go could be to change the page_migration to use
> replace_page (or __replace_page if called in some shared inner-lock
> context) after preparing the newpage to be a regular VM page. If we
> can do that, migrate.c will get the o_direct race fixed too for free.

Define a regular VM page? A page on the LRU?