Re: [PATCH 1/2] mm: Take all anon_vma locks in anon_vma_lock

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

On Thu, Apr 29, 2010 at 5:32 PM, Mel Gorman <mel@csn.ul.ie> wrote:
> From: Rik van Riel <riel@redhat.com>
>
> Take all the locks for all the anon_vmas in anon_vma_lock, this properly
> excludes migration and the transparent hugepage code from VMA changes done
> by mmap/munmap/mprotect/expand_stack/etc...
>
> Unfortunately, this requires adding a new lock (mm->anon_vma_chain_lock),
> otherwise we have an unavoidable lock ordering conflict.  This changes the
> locking rules for the "same_vma" list to be either mm->mmap_sem for write,
> or mm->mmap_sem for read plus the new mm->anon_vma_chain lock.  This limits
> the place where the new lock is taken to 2 locations - anon_vma_prepare and
> expand_downwards.
>
> Document the locking rules for the same_vma list in the anon_vma_chain and
> remove the anon_vma_lock call from expand_upwards, which does not need it.
>
> Signed-off-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>

I like this one.

Although it try to lock the number of anon_vmas attached to a VMA ,
it's small so latency couldn't be big. :)
It's height problem not width problem of tree. :)

Thanks, Rik.
-- 
Kind regards,
Minchan Kim

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