On Wed, 5 May 2010, Mel Gorman wrote: > > With the recent anon_vma changes, there can be more than one anon_vma->lock > to take in a anon_vma_chain but a second lock cannot be spinned upon in case > of deadlock. The rmap walker tries to take locks of different anon_vma's > but if the attempt fails, locks are released and the operation is restarted. Btw, is this really needed? Nobody else takes two anon_vma locks at the same time, so in order to avoid ABBA deadlocks all we need to guarantee is that rmap_walk_ksm() and rmap_walk_anon() always lock the anon_vma's in the same order. And they do, as far as I can tell. How could we ever get a deadlock when we have both cases doing the locking by walking the same_anon_vma list? list_for_each_entry(avc, &anon_vma->head, same_anon_vma) { So I think the "retry" logic looks unnecessary, and actually opens us up to a possible livelock bug (imagine a long chain, and heavy page fault activity elsewhere that ends up locking some anon_vma in the chain, and just the right behavior that gets us into a lockstep situation), rather than fixing an ABBA deadlock. Now, if it's true that somebody else _does_ do nested anon_vma locking, I'm obviously wrong. But I don't see such usage. Comments? Linus -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>