On Tue 04-06-13 14:14:45, Frank Mehnert wrote: > On Tuesday 04 June 2013 13:58:07 Robin Holt wrote: > > This is probably more appropriate to be directed at the linux-mm > > mailing list. > > > > On Tue, Jun 04, 2013 at 09:22:10AM +0200, Frank Mehnert wrote: > > > Hi, > > > > > > our memory management on Linux hosts conflicts with NUMA page migration. > > > I assume this problem existed for a longer time but Linux 3.8 introduced > > > automatic NUMA page balancing which makes the problem visible on > > > multi-node hosts leading to kernel oopses. > > > > > > NUMA page migration means that the physical address of a page changes. > > > This is fatal if the application assumes that this never happens for > > > that page as it was supposed to be pinned. > > > > > > We have two kind of pinned memory: > > > > > > A) 1. allocate memory in userland with mmap() > > > > > > 2. madvise(MADV_DONTFORK) > > > 3. pin with get_user_pages(). > > > 4. flush dcache_page() > > > 5. vm_flags |= (VM_DONTCOPY | VM_LOCKED) > > > > > > (resulting flags are VM_MIXEDMAP | VM_DONTDUMP | VM_DONTEXPAND | > > > > > > VM_DONTCOPY | VM_LOCKED | 0xff) > > > > I don't think this type of allocation should be affected. The > > get_user_pages() call should elevate the pages reference count which > > should prevent migration from completing. I would, however, wait for > > a more definitive answer. > > Thanks Robin! Actually case B) is more important for us so I'm waiting > for more feedback :) The manual node migration code seems to be OK in case B as well because Reserved are skipped (check check_pte_range called from down the do_migrate_pages path). Maybe auto-numa code is missing this check assuming that it cannot encounter reserved pages. migrate_misplaced_page relies on numamigrate_isolate_page which relies on isolate_lru_page and that one expects a LRU page. Is your Reserved page on the LRU list? That would be a bit unexpected. -- 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>