* Mel Gorman <mgorman@xxxxxxx> wrote: > On Mon, Oct 07, 2013 at 11:28:38AM +0100, Mel Gorman wrote: > > This series has roughly the same goals as previous versions despite the > > size. It reduces overhead of automatic balancing through scan rate reduction > > and the avoidance of TLB flushes. It selects a preferred node and moves tasks > > towards their memory as well as moving memory toward their task. It handles > > shared pages and groups related tasks together. Some problems such as shared > > page interleaving and properly dealing with processes that are larger than > > a node are being deferred. This version should be ready for wider testing > > in -tip. > > > > Hi Ingo, > > Off-list we talked with Peter about the fact that automatic NUMA > balancing as merged in 3.10, 3.11 and 3.12 shortly may corrupt > userspace memory. There is one LKML report on this that I'm aware of -- > https://lkml.org/lkml/2013/7/31/647 which I prompt forgot to follow up > properly on . The user-visible effect is that pages get filled with zeros > with results such as null pointer exceptions in JVMs. It is fairly difficult > to trigger but it became much easier to trigger during the development of > the series "Basic scheduler support for automatic NUMA balancing" which > is how it was discovered and finally fixed. > > In that series I tagged patches 2-9 for -stable as these patches addressed > the problem for me. I did not call it out as clearly as I should have > and did not realise the cc: stable tags were stripped. Worse, as it was > close to the release and the bug is relatively old I was ok with waiting > until 3.12 came out and then treat it as a -stable backport. It has been > highlighted that this is the wrong attitude and we should consider merging > the fixes now and backporting to -stable sooner rather than later. > > The most important patches are > > mm: Wait for THP migrations to complete during NUMA hinting fault > mm: Prevent parallel splits during THP migration > mm: Close races between THP migration and PMD numa clearing > > but on their own they will cause conflicts with tricky fixups and -stable > would differ from mainline in annoying ways. Patches 2-9 have been heavily > tested in isolation so I'm reasonably confident they fix the problem and are > -stable material. While strictly speaking not all the patches are required > for the fix, the -stable kernels would then be directly comparable with > 3.13 when the full NUMA balancing series is applied. If I rework them at > this point then I'll also have to retest delaying things until next week. > > Please consider queueing patches 2-9 for 3.12 via -urgent if it is > not too late and preserve the cc: stable tags so Greg will pick > them up automatically. Would be nice if you gave me all the specific SHA1 tags of sched/core that are required for the fix. We can certainly use a range to make it all safer to apply. Thanks, Ingo -- 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>