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From: Rik van Riel on 12 May 2010 13:50
This patch series implements Linus's suggestion of always locking the
root anon_vma. Because the lock in other anon_vmas no longer protects
anything at all, we cannot do the "lock dance" that Mel's earlier
patches implements and instead need a root pointer in the anon_vma.
The only subtlety these patches rely on is that the same_vma list
is ordered from new to old, with the root anon_vma at the very end.
This, together with the forward list walking in unlink_anon_vmas,
ensures that the root anon_vma is the last one freed.
The KSM refcount adds some additional complexity, because an anon_vma
can stick around after the processes it was attached to have already
exited. Patch 5/5 deals with that issue.
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