On Wed, May 07, 2008 at 03:31:03PM -0700, Andrew Morton wrote:
quoted text
> Nope.  We only need to take the global lock before taking *two or more* of
> the per-vma locks.
> 
> I really wish I'd thought of that.

I don't see how you can avoid taking the system-wide-global lock
before every single anon_vma->lock/i_mmap_lock out there without
mm_lock.

Please note, we can't allow a thread to be in the middle of
zap_page_range while mmu_notifier_register runs.

vmtruncate takes 1 single lock, the i_mmap_lock of the inode. Not more
than one lock and we've to still take the global-system-wide lock
_before_ this single i_mmap_lock and no other lock at all.

Please elaborate, thanks!
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