I tried your patch with warn_alloc() torture. It did not cause lockups. But I felt that possibility of failing to flush last second messages (such as SysRq-c or SysRq-b) to consoles has increased. Is this psychological? ---------- vmcore-dmesg start ---------- [ 169.016198] postgres cpuset= [ 169.032544] filemap_fault+0x311/0x790 [ 169.047745] / [ 169.047780] mems_allowed=0 [ 169.050577] ? xfs_ilock+0x126/0x1a0 [xfs] [ 169.062769] mems_allowed=0 [ 169.065754] ? down_read_nested+0x3a/0x60 [ 169.065783] ? xfs_ilock+0x126/0x1a0 [xfs] [ 189.700206] sysrq: SysRq : [ 189.700639] __xfs_filemap_fault.isra.19+0x3f/0xe0 [xfs] [ 189.700799] xfs_filemap_fault+0xb/0x10 [xfs] [ 189.703981] Trigger a crash [ 189.707032] __do_fault+0x19/0xa0 [ 189.710008] BUG: unable to handle kernel [ 189.713387] __handle_mm_fault+0xbb3/0xda0 [ 189.716473] NULL pointer dereference [ 189.719674] handle_mm_fault+0x14f/0x300 [ 189.722969] at (null) [ 189.722974] IP: sysrq_handle_crash+0x3b/0x70 [ 189.726156] ? handle_mm_fault+0x39/0x300 [ 189.729537] PGD 1170dc067 [ 189.732841] __do_page_fault+0x23e/0x4f0 [ 189.735876] P4D 1170dc067 [ 189.739171] do_page_fault+0x30/0x80 [ 189.742323] PUD 1170dd067 [ 189.745437] page_fault+0x22/0x30 [ 189.748329] PMD 0 [ 189.751106] RIP: 0033:0x650390 [ 189.756583] RSP: 002b:00007fffef6b1568 EFLAGS: 00010246 [ 189.759574] Oops: 0002 [#1] SMP DEBUG_PAGEALLOC [ 189.762607] RAX: 0000000000000000 RBX: 00007fffef6b1594 RCX: 00007fae949caa20 [ 189.765665] Modules linked in: [ 189.768423] RDX: 0000000000000008 RSI: 0000000000000000 RDI: 0000000000000000 [ 189.768425] RBP: 00007fffef6b1590 R08: 0000000000000002 R09: 0000000000000010 [ 189.771478] ip6t_rpfilter [ 189.774297] R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000 [ 189.777016] ipt_REJECT [ 189.779366] R13: 0000000000000000 R14: 00007fae969787e0 R15: 0000000000000004 [ 189.782114] nf_reject_ipv4 [ 189.784839] CPU: 7 PID: 6959 Comm: sleep Not tainted 4.14.0-rc8+ #302 [ 189.785113] Mem-Info: ---------- vmcore-dmesg end ---------- ---------- serial console start ---------- [ 168.975447] Mem-Info: [ 168.975453] active_anon:827953 inactive_anon:3376 isolated_anon:0 [ 168.975453] active_file:55 inactive_file:449 isolated_file:246 [ 168.975453] unevictable:0 dirty:2 writeback:68 unstable:0 [ 168.975453] slab_reclaimable:4344 slab_unreclaimable:36066 [ 168.975453] mapped:2250 shmem:3543 pagetables:9568 bounce:0 [ 168.975453] free:21398 free_pcp:175 free_cma:0 [ 168.975458] Node 0 active_anon:3311812kB inactive_anon:13504kB active_file:220kB inactive_file:1796kB unevictable:0kB isolated(anon):0kB isolated(file):984kB mapped:9000kB dirty:8kB writeback:272kB shmem:14172kB shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 2869248kB writeback_tmp:0kB unstable:0kB all_unreclaimable? no [ 168.975460] Node 0 DMA free:14756kB min:288kB low:360kB high:432kB active_anon:1088kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:15988kB managed:15904kB mlocked:0kB kernel_stack:0kB pagetables:28kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB [ 168.975482] lowmem_reserve[]: 0 2686 3619 3619 [ 168.975489] Node 0 DMA32 free:53624kB min:49956kB low:62444kB high:74932kB active_anon:2691088kB inactive_anon:16kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:3129152kB managed:2751400kB mlocked:0kB kernel_stack:32kB pagetables:4232kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB [ 168.975494] lowmem_reserve[]: 0 0 932 932 [ 168.975501] Node 0 Normal free:17212kB min:17336kB low:21668kB high:26000kB active_anon:619636kB inactive_anon:13488kB active_file:220kB inactive_file:2872kB unevictable:0kB writepending:280kB present:1048576kB managed:954828kB mlocked:0kB kernel_stack:22784kB pagetables:34012kB bounce:0kB free_pcp:700kB local_pcp:40kB free_cma:0kB [ 168.975505] lowmem_reserve[]: 0 0 0 0 [ 168.975512] Node 0 DMA: 1*4kB (U) 0*8kB 0*16kB 1*32kB (U) 2*64kB (UM) 2*128kB (UM) 2*256kB (UM) 1*512kB (M) 1*1024kB (U) 0*2048kB 3*4096kB (M) = 14756kB [ 168.975536] Node 0 DMA32: 18*4kB (U) 14*8kB (UM) 14*16kB (UE) 37*32kB (UE) 9*64kB (UE) 4*128kB (UME) 1*256kB (M) 3*512kB (UME) 2*1024kB (UE) 3*2048kB (UME) 10*4096kB (M) = 53624kB [ 0.000000] Linux version 4.14.0-rc8+ (root@localhost.localdomain) (gcc version 4.8.5 20150623 (Red Hat 4.8.5-16) (GCC)) #302 SMP Mon Nov 6 12:15:00 JST 2017 [ 0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-4.14.0-rc8+ root=UUID=98df1583-260a-423a-a193-182dade5d085 ro security=none sysrq_always_enabled console=ttyS0,115200n8 console=tty0 LANG=en_US.UTF-8 irqpoll nr_cpus=1 reset_devices cgroup_disable=memory mce=off numa=off udev.children-max=2 panic=10 rootflags=nofail acpi_no_memhotplug transparent_hugepage=never disable_cpu_apicid=0 elfcorehdr=867704K ---------- serial console end ---------- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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