Re: [PATCH 5/5] extend KSM refcounts to the anon_vma root

[Minchan Kim <minchan.kim@gmail.com>]

On Wed, May 26, 2010 at 03:41:24PM -0400, Rik van Riel wrote:
> Subject: extend KSM refcounts to the anon_vma root
> 
> KSM reference counts can cause an anon_vma to exist after the processe
> it belongs to have already exited.  Because the anon_vma lock now lives
> in the root anon_vma, we need to ensure that the root anon_vma stays
> around until after all the "child" anon_vmas have been freed.
> 
> The obvious way to do this is to have a "child" anon_vma take a
> reference to the root in anon_vma_fork.  When the anon_vma is freed
> at munmap or process exit, we drop the refcount in anon_vma_unlink
> and possibly free the root anon_vma.
> 
> The KSM anon_vma reference count function also needs to be modified
> to deal with the possibility of freeing 2 levels of anon_vma.  The
> easiest way to do this is to break out the KSM magic and make it
> generic.
> 
> When compiling without CONFIG_KSM, this code is compiled out.
> 
> Signed-off-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>

Now I understand this patch. 
Thanks, Rik. 
-- 
Kind regards,
Minchan Kim