On Thu, May 06, 2010 at 06:40:39PM -0700, Linus Torvalds wrote: > On Fri, 7 May 2010, Mel Gorman wrote: > > > > Page migration requires rmap to be able to find all migration ptes > > created by migration. If the second rmap_walk clearing migration PTEs > > misses an entry, it is left dangling causing a BUG_ON to trigger during > > fault. For example; > > So I still absolutely detest this patch. > > Why didn't the other - much simpler - patch work? The one Rik pointed to: > > http://lkml.org/lkml/2010/4/30/198 > Oh, it works, but it depends on a magic check is_vma_temporary_stack(). Kamezawa had a variant that did not depend on magic but it increased the size of vm_area_struct. That magic check was just something that would be easy to break and not spot hence the temporary VMA instead. > and didn't do that _disgusting_ temporary anon_vma? > > Alternatively, why don't we just take the anon_vma lock over this region, > so that rmap can't _walk_ the damn thing? > Because move_page_tables() calls into the page allocator. I'll create a version that allocates the PMDs in advance and see what it looks like. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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>