On 05/05/2014 11:50 AM, Vlastimil Babka wrote: > On 05/05/2014 04:36 PM, Sasha Levin wrote: >> On 05/02/2014 08:08 AM, Vlastimil Babka wrote: >>> On 04/30/2014 11:46 PM, Sasha Levin wrote: >>>>> On 04/03/2014 11:40 AM, Vlastimil Babka wrote: >>>>>>> For the MIGRATE_RESERVE pages, it is important they do not get misplaced >>>>>>> on free_list of other migratetype, otherwise the whole MIGRATE_RESERVE >>>>>>> pageblock might be changed to other migratetype in try_to_steal_freepages(). >>>>>>> For MIGRATE_CMA, the pages also must not go to a different free_list, otherwise >>>>>>> they could get allocated as unmovable and result in CMA failure. >>>>>>> >>>>>>> This is ensured by setting the freepage_migratetype appropriately when placing >>>>>>> pages on pcp lists, and using the information when releasing them back to >>>>>>> free_list. It is also assumed that CMA and RESERVE pageblocks are created only >>>>>>> in the init phase. This patch adds DEBUG_VM checks to catch any regressions >>>>>>> introduced for this invariant. >>>>>>> >>>>>>> Cc: Yong-Taek Lee <ytk.lee@xxxxxxxxxxx> >>>>>>> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx> >>>>>>> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> >>>>>>> Cc: Mel Gorman <mgorman@xxxxxxx> >>>>>>> Cc: Minchan Kim <minchan@xxxxxxxxxx> >>>>>>> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> >>>>>>> Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> >>>>>>> Cc: Hugh Dickins <hughd@xxxxxxxxxx> >>>>>>> Cc: Rik van Riel <riel@xxxxxxxxxx> >>>>>>> Cc: Michal Nazarewicz <mina86@xxxxxxxxxx> >>>>>>> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> >>>>> >>>>> Two issues with this patch. >>>>> >>>>> First: >>>>> >>>>> [ 3446.320082] kernel BUG at mm/page_alloc.c:1197! >>>>> [ 3446.320082] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC >>>>> [ 3446.320082] Dumping ftrace buffer: >>>>> [ 3446.320082] (ftrace buffer empty) >>>>> [ 3446.320082] Modules linked in: >>>>> [ 3446.320082] CPU: 1 PID: 8923 Comm: trinity-c42 Not tainted 3.15.0-rc3-next-20140429-sasha-00015-g7c7e0a7-dirty #427 >>>>> [ 3446.320082] task: ffff88053e208000 ti: ffff88053e246000 task.ti: ffff88053e246000 >>>>> [ 3446.320082] RIP: get_page_from_freelist (mm/page_alloc.c:1197 mm/page_alloc.c:1548 mm/page_alloc.c:2036) >>>>> [ 3446.320082] RSP: 0018:ffff88053e247778 EFLAGS: 00010002 >>>>> [ 3446.320082] RAX: 0000000000000003 RBX: ffffea0000f40000 RCX: 0000000000000008 >>>>> [ 3446.320082] RDX: 0000000000000002 RSI: 0000000000000003 RDI: 00000000000000a0 >>>>> [ 3446.320082] RBP: ffff88053e247868 R08: 0000000000000007 R09: 0000000000000000 >>>>> [ 3446.320082] R10: ffff88006ffcef00 R11: 0000000000000000 R12: 0000000000000014 >>>>> [ 3446.335888] R13: ffffea000115ffe0 R14: ffffea000115ffe0 R15: 0000000000000000 >>>>> [ 3446.335888] FS: 00007f8c9f059700(0000) GS:ffff88006ec00000(0000) knlGS:0000000000000000 >>>>> [ 3446.335888] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b >>>>> [ 3446.335888] CR2: 0000000002cbc048 CR3: 000000054cdb4000 CR4: 00000000000006a0 >>>>> [ 3446.335888] DR0: 00000000006de000 DR1: 00000000006de000 DR2: 0000000000000000 >>>>> [ 3446.335888] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000602 >>>>> [ 3446.335888] Stack: >>>>> [ 3446.335888] ffff88053e247798 ffff88006eddc0b8 0000000000000016 0000000000000000 >>>>> [ 3446.335888] ffff88006ffd2068 ffff88006ffdb008 0000000100000000 0000000000000000 >>>>> [ 3446.335888] ffff88006ffdb000 0000000000000000 0000000000000003 0000000000000001 >>>>> [ 3446.335888] Call Trace: >>>>> [ 3446.335888] __alloc_pages_nodemask (mm/page_alloc.c:2731) >>>>> [ 3446.335888] ? __this_cpu_preempt_check (lib/smp_processor_id.c:63) >>>>> [ 3446.335888] alloc_pages_vma (include/linux/mempolicy.h:76 mm/mempolicy.c:1998) >>>>> [ 3446.335888] ? shmem_alloc_page (mm/shmem.c:881) >>>>> [ 3446.335888] ? kvm_clock_read (arch/x86/include/asm/preempt.h:90 arch/x86/kernel/kvmclock.c:86) >>>>> [ 3446.335888] shmem_alloc_page (mm/shmem.c:881) >>>>> [ 3446.335888] ? __const_udelay (arch/x86/lib/delay.c:126) >>>>> [ 3446.335888] ? __rcu_read_unlock (kernel/rcu/update.c:97) >>>>> [ 3446.335888] ? find_get_entry (mm/filemap.c:979) >>>>> [ 3446.335888] ? find_get_entry (mm/filemap.c:940) >>>>> [ 3446.335888] ? find_lock_entry (mm/filemap.c:1024) >>>>> [ 3446.335888] shmem_getpage_gfp (mm/shmem.c:1130) >>>>> [ 3446.335888] ? sched_clock_local (kernel/sched/clock.c:214) >>>>> [ 3446.335888] ? do_read_fault.isra.42 (mm/memory.c:3523) >>>>> [ 3446.335888] shmem_fault (mm/shmem.c:1237) >>>>> [ 3446.335888] ? do_read_fault.isra.42 (mm/memory.c:3523) >>>>> [ 3446.335888] __do_fault (mm/memory.c:3344) >>>>> [ 3446.335888] ? _raw_spin_unlock (arch/x86/include/asm/preempt.h:98 include/linux/spinlock_api_smp.h:152 kernel/locking/spinlock.c:183) >>>>> [ 3446.335888] do_read_fault.isra.42 (mm/memory.c:3524) >>>>> [ 3446.335888] ? get_parent_ip (kernel/sched/core.c:2485) >>>>> [ 3446.335888] ? get_parent_ip (kernel/sched/core.c:2485) >>>>> [ 3446.335888] __handle_mm_fault (mm/memory.c:3662 mm/memory.c:3823 mm/memory.c:3950) >>>>> [ 3446.335888] ? __const_udelay (arch/x86/lib/delay.c:126) >>>>> [ 3446.335888] ? __rcu_read_unlock (kernel/rcu/update.c:97) >>>>> [ 3446.335888] handle_mm_fault (mm/memory.c:3973) >>>>> [ 3446.335888] __get_user_pages (mm/memory.c:1863) >>>>> [ 3446.335888] ? preempt_count_sub (kernel/sched/core.c:2541) >>>>> [ 3446.335888] __mlock_vma_pages_range (mm/mlock.c:255) >>>>> [ 3446.335888] __mm_populate (mm/mlock.c:711) >>>>> [ 3446.335888] vm_mmap_pgoff (include/linux/mm.h:1841 mm/util.c:402) >>>>> [ 3446.335888] SyS_mmap_pgoff (mm/mmap.c:1378) >>>>> [ 3446.335888] ? syscall_trace_enter (include/linux/context_tracking.h:27 arch/x86/kernel/ptrace.c:1461) >>>>> [ 3446.335888] ia32_do_call (arch/x86/ia32/ia32entry.S:430) >>>>> [ 3446.335888] Code: 00 66 0f 1f 44 00 00 ba 02 00 00 00 31 f6 48 89 c7 e8 c1 c3 ff ff 48 8b 53 10 83 f8 03 74 08 83 f8 04 75 13 0f 1f 00 39 d0 74 0c <0f> 0b 66 2e 0f 1f 84 00 00 00 00 00 45 85 ff 75 15 49 8b 55 00 >>>>> [ 3446.335888] RIP get_page_from_freelist (mm/page_alloc.c:1197 mm/page_alloc.c:1548 mm/page_alloc.c:2036) >>>>> [ 3446.335888] RSP <ffff88053e247778> >>> Hey, that's not an issue, that means the patch works as intended :) And >>> I believe it's not a bug introduced by PATCH 1/2. >>> >>> So, according to my decodecode reading, RAX is the results of >>> get_pageblock_migratetype() and it's MIGRATE_RESERVE. RDX is the result >>> of get_freepage_migratetype() and it's MIGRATE_UNMOVABLE. The >>> freepage_migratetype has just been set either by __rmqueue_smallest() or >>> __rmqueue_fallback(), according to the free_list the page has been taken >>> from. So this looks like a page from MIGRATE_RESERVE pageblock found on >>> the !MIGRATE_RESERVE free_list, which is exactly what the patch intends >>> to catch. >>> >>> I think there are two possible explanations. >>> >>> 1) the pageblock is genuinely MIGRATE_RESERVE and it was misplaced by >>> mistake. I think it wasn't in free_pcppages_bulk() as there's the same >>> VM_BUG_ON which would supposedly trigger at the moment of displacing. In >>> theory it's possible that there's a race through __free_pages_ok() -> >>> free_one_page() where the get_pageblock_migratetype() in >>> __free_pages_ok() would race with set_pageblock_migratetype() and result >>> in bogus value. But nobody should be calling set_pageblock_migratetype() >>> on a MIGRATE_RESERVE pageblock. >>> >>> 2) the pageblock was marked as MIGRATE_RESERVE due to a race between >>> set_pageblock_migratetype() and set_pageblock_skip(). The latter is >>> currently not serialized by zone->lock, nor it uses atomic bit set. So >>> it may result in lost updates in a racing set_pageblock_migratetype(). I >>> think a well-placed race when changing pageblock from MIGRATE_MOVABLE to >>> MIGRATE_RECLAIMABLE could result in MIGRATE_RESERVE value. Similar races >>> have been already observed to be a problem where frequent changing >>> to/from MIGRATE_ISOLATE is involved, and I did a patch series to address >>> this, but it was not complete and I postponed it after Mel's changes >>> that remove the racy for-cycles completely. So it might be that his >>> "[PATCH 08/17] mm: page_alloc: Use word-based accesses for get/set >>> pageblock bitmaps" already solves this bug (but maybe only on certain >>> architectures where you don't need atomic operations). You might try >>> that patch if you can reproduce this bug frequently enough? >> >> I've tried that patch, but still see the same BUG_ON. > > Oh damn, I've realized that my assumptions about MIGRATE_RESERVE pageblocks being created only on zone init time were wrong. setup_zone_migrate_reserve() is called also from the handler of min_free_kbytes sysctl... does trinity try to change that while running? There's nothing that will prevent it from changing that. Thanks, Sasha -- 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>