On Mon, Nov 03, 2014 at 10:04:24PM -0800, Hugh Dickins wrote: > I'm glad to see this series back, and nicely presented: thank you. > Not worth respinning them, but consider 1,2,3,4,5,6,7 and 9 as > Acked-by: Hugh Dickins <hughd@xxxxxxxxxx> > > On Thu, 30 Oct 2014, Davidlohr Bueso wrote: > > > As per the comment in move_ptes(), we only require taking the > > anon vma and i_mmap locks to ensure that rmap will always observe > > either the old or new ptes, in the case of need_rmap_lock=true. > > No modifications to the tree itself, thus share the i_mmap_rwsem. > > > > Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx> > > Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > > But this one is Nacked by me. I don't understand how you and Kirill > could read Michel's painstaking comment on need_rmap_locks, then go > go ahead and remove the exclusion of rmap_walk(). > > I agree the code here does not modify the interval tree, but the > comment explains how we're moving a pte from one place in the tree > to another, and in some cases there's a danger that the rmap walk > might miss the pte from both places (which doesn't matter much to > most of its uses, but is critical in page migration). > > Or am I the one missing something? You're completely right. I've seen the comment (and I've added the missed need_rmap_locks case for move_huge_pmd() before). What happened is I've over-extrapolated my experience of rmap walk in case of split_huge_page(), which takes exclusive anon_vma lock, to the rest of rmap use-cases. This of course was hugely wrong. I'm ashamed and feel really bad about the situation. Sorry. -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>