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



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