On Wed, Dec 07, 2011 at 07:24:59PM -0800, David Rientjes wrote: > On Sat, 5 Nov 2011, Andrea Arcangeli wrote: > > > migrate was doing a rmap_walk with speculative lock-less access on > > pagetables. That could lead it to not serialize properly against > > mremap PT locks. But a second problem remains in the order of vmas in > > the same_anon_vma list used by the rmap_walk. > > > > If vma_merge would succeed in copy_vma, the src vma could be placed > > after the dst vma in the same_anon_vma list. That could still lead > > migrate to miss some pte. > > > > This patch adds a anon_vma_moveto_tail() function to force the dst vma > > at the end of the list before mremap starts to solve the problem. > > > > If the mremap is very large and there are a lots of parents or childs > > sharing the anon_vma root lock, this should still scale better than > > taking the anon_vma root lock around every pte copy practically for > > the whole duration of mremap. > > > > Update: Hugh noticed special care is needed in the error path where > > move_page_tables goes in the reverse direction, a second > > anon_vma_moveto_tail() call is needed in the error path. > > > > Is this still needed? It's missing in linux-next. Yes it's needed, either this or the anon_vma lock around move_page_tables. Then we also need the i_mmap_mutex around fork or a triple loop in vmtruncate (then we could remove i_mmap_mutex in mremap). -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>