Re: [RFC 5/6] Swapless V1: Rip out swap migration code

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Tue, 4 Apr 2006 08:06:26 -0700 (PDT)
Christoph Lameter <clameter@sgi.com> wrote:

> On Tue, 4 Apr 2006, KAMEZAWA Hiroyuki wrote:
> 
> > On Mon, 3 Apr 2006 23:58:05 -0700 (PDT)
> > Christoph Lameter <clameter@sgi.com> wrote:
> > 
> > > Rip the page migration logic out
> > > 
> > 
> > Thank you. I like this removal, especially removing remove_from_swap() :)
> 
> Have a look at remove_migration_ptes(). Like remove_from_swap() it has the 
> requirement that the mmap_sem is held since that is the only secure way to 
> make sure that the anon_vma is not vanishing from under us. That may be a 
> problem if you are not coming from a process context. Any ideas on how to 
> fix that?
> 
I think adding SWP_TYPE_MIGRATION consideration to free_swap_and_cache() is
enough against anon_vma vanishing. Because remove_migration_ptes() compares 
old pte entry with old page's pfn, a page cannot be remapped into old place
when anon_vma has gone. This is my first impression.
My concern is refcnt handling of SWP_TYPE_MIGRATION pages, but maybe no problem.

Note: unuse_vma() doesn't check what pte entry contains.

-Kame



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