On Mon, Apr 26, 2010 at 06:48:42PM +0900, Minchan Kim wrote: > On Mon, Apr 26, 2010 at 6:28 PM, KAMEZAWA Hiroyuki > <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > > On Mon, 26 Apr 2010 08:49:01 +0900 > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > > > >> On Sat, 24 Apr 2010 11:43:24 +0100 > >> Mel Gorman <mel@xxxxxxxxx> wrote: > > > >> > It looks nice but it still broke after 28 hours of running. The > >> > seq-counter is still insufficient to catch all changes that are made to > >> > the list. I'm beginning to wonder if a) this really can be fully safely > >> > locked with the anon_vma changes and b) if it has to be a spinlock to > >> > catch the majority of cases but still a lazy cleanup if there happens to > >> > be a race. It's unsatisfactory and I'm expecting I'll either have some > >> > insight to the new anon_vma changes that allow it to be locked or Rik > >> > knows how to restore the original behaviour which as Andrea pointed out > >> > was safe. > >> > > >> Ouch. > > > > Ok, reproduced. Here is status in my test + printk(). > > > > * A race doesn't seem to happen if swap=off. > > I need to swapon to cause the bug > > FYI, > > Do you have a swapon/off bomb test? > When I saw your mail, I feel it might be culprit. > > http://lkml.org/lkml/2010/4/22/762. > > It is just guessing. I don't have a time to look into, now. > I haven't tried a swapon/off test but that patch is certainly important and closes an important race. A fork-heavy test will routinely hit the problem and applying the patch makes it very difficult to reproduce the problem. I've added it to my stack while I continue trying to pin down when the VMA-changes make a difference. I'm relooking at the seq counter approach. It appears to very rare the logic is actually triggered so reproducing is a problem. I'm still not convinced that just locking anon_vma is not the answer there. If it locks and as expand_downwards already locks and with the fork-based patch, I think the races might be closed but I'm not 100% certain yet. -- 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>