Re: [PATCH 4/5] always lock the root (oldest) anon_vma

[KAMEZAWA Hiroyuki]

On Wed, 26 May 2010 15:40:44 -0400
Rik van Riel <riel@xxxxxxxxxx> wrote:

> Subject: always lock the root (oldest) anon_vma
> 
> Always (and only) lock the root (oldest) anon_vma whenever we do something in an
> anon_vma.  The recently introduced anon_vma scalability is due to the rmap code
> scanning only the VMAs that need to be scanned.  Many common operations still
> took the anon_vma lock on the root anon_vma, so always taking that lock is not
> expected to introduce any scalability issues.
> 
> However, always taking the same lock does mean we only need to take one lock,
> which means rmap_walk on pages from any anon_vma in the vma is excluded from
> occurring during an munmap, expand_stack or other operation that needs to
> exclude rmap_walk and similar functions.
> 
> Also add the proper locking to vma_adjust.
> 
> Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>

Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>



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