On Wed 05-06-13 03:22:32, Frank Mehnert wrote: > On Wednesday 05 June 2013 11:56:30 Michal Hocko wrote: > > On Wed 05-06-13 11:32:15, Frank Mehnert wrote: > > [...] > > > > > Thank you very much for your help. As I said, this problem happens _only_ > > > with NUMA_BALANCING enabled. I understand that you treat the VirtualBox > > > code as untrusted but the reason for the problem is that some assumption > > > is obviously not met: The VirtualBox code assumes that the memory it > > > allocates using case A and case B is > > > > > > 1. always present and > > > 2. will always be backed by the same phyiscal memory > > > > > > over the entire life time. Enabling NUMA_BALANCING seems to make this > > > assumption false. I only want to know why. > > > > As I said earlier. Both the manual node migration and numa_fault handler > > do not migrate pages with elevated ref count (your A case) and pages > > that are not on the LRU. So if your Referenced pages might be on the LRU > > then you probably have to look into numamigrate_isolate_page and do an > > exception for PageReserved pages. But I am a bit suspicious this is the > > cause because the reclaim doesn't consider PageReserved pages either so > > they could get reclaimed. Or maybe you have handled that path in your > > kernel. > > Thanks, I will also investigate into this direction. > > > Or the other option is that you depend on a timing or something like > > that which doesn't hold anymore. That would be hard to debug though. > > > > > I see, you don't believe me. I will add more code to the kernel logging > > > which pages were migrated. > > > > Simple test for PageReserved flag in numamigrate_isolate_page should > > tell you more. > > > > This would cover the migration part. Another potential problem could be > > that the page might get unmapped and marked for the numa fault (see > > do_numa_page). So maybe your code just assumes that the page even > > doesn't get unmapped? > > Exactly, that's the assumption -- therefore all these vm_flags tricks. > If this assumption is wrong or not always true, can this requirement > (page is _never_ unmapped) be met at all? yes, just pin the page by get_page(). Reserved pages are usually not touched because they are not sitting in the LRU (that just doesn't make any sense) - why we would age such pages in the first place. -- Michal Hocko SUSE Labs -- 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>