chu*_*utz 12 troubleshooting server-crashes memory-leak oom centos6
服务器在多次“内存不足”消息后崩溃，我试图查明罪魁祸首。如果它在用户空间 - 哪个进程。如果它在内核中 - 哪个内核模块。
我试图找出如何使用崩溃实用程序来调查是什么触发了服务器上的 OOM。
作为安装一对新服务器的一部分，我开始了一个 14TB DRBD设备的初始化。大约在那个时候，在使用 DRBD 同步器速率配置并启动和关闭一些绑定的网络接口时，其中一台服务器崩溃了。在 30 秒的时间内，它产生了 39 条Out of memory: Kill process ####消息。然后它崩溃了：
Kernel panic - not syncing: Out of memory and no killable processes...
系统崩溃触发了kdump。现在我有一个不错的vmcore.flat文件，应该可以直接使用它来调查问题，但是我很难找出所有内存的去向。
我知道的唯一资源是Dedoimedo 的网站，它有很好的说明，以及内核崩溃手册。这些也恰好是答案中建议的唯一资源，所以我认为这crash是唯一的调查方法。
如果有另一种方式对事件进行事后分析，我愿意接受。这只是crash我所知道的唯一实用程序。我现在拥有的只是vmcore.flat文件，我需要知道的是哪个组件占用了所有内存。我怀疑是内核模块问题，更具体地说是绑定模块之一（因为它在我关闭接口时被触发）、DRBD 模块（在 CentOS 6.3 上用树构建的版本 8.3.15），或其中一个10G 以太网模块（mlnx_en构建在树外，即我关闭的接口，或树内bnx2x，即保持活动状态的接口）。我只需要知道是否有办法验证我的怀疑。
到目前为止，我只设法使用crash实用程序提取了以下信息：
检查使用了多少内存
$ crash /usr/lib/debug/lib/modules/2.6.32-279.5.2.el6.x86_64/vmlinux vmcore.flat
....
crash> kmem -i
PAGES TOTAL PERCENTAGE
TOTAL MEM 16482587 62.9 GB ----
FREE 54610 213.3 MB 0% of TOTAL MEM
USED 16427977 62.7 GB 99% of TOTAL MEM
SHARED 4683 18.3 MB 0% of TOTAL MEM
BUFFERS 118 472 KB 0% of TOTAL MEM
CACHED 82 328 KB 0% of TOTAL MEM
SLAB 46635 182.2 MB 0% of TOTAL MEM
TOTAL SWAP 0 0 ----
SWAP USED 0 0 100% of TOTAL SWAP
SWAP FREE 0 0 0% of TOTAL SWAP
显然，它耗尽了内存。所有 64G 都没有了……但是在哪里？
尝试查看是否有任何进程正在泄漏内存
唯一似乎相关ps的ps命令是（这是 的子命令crash）。它没有显示任何异常，但它也没有显示内核线程。
crash> ps
PID PPID CPU TASK ST %MEM VSZ RSS COMM
0 0 0 ffffffff81a8d020 RU 0.0 0 0 [swapper]
> 0 0 1 ffff88102c456040 RU 0.0 0 0 [swapper]
> 0 0 2 ffff88082c772aa0 RU 0.0 0 0 [swapper]
> 0 0 3 ffff88102c456aa0 RU 0.0 0 0 [swapper]
0 0 4 ffff88082c7b8ae0 RU 0.0 0 0 [swapper]
> 0 0 5 ffff88102c457500 RU 0.0 0 0 [swapper]
> 0 0 6 ffff88082c7d6aa0 RU 0.0 0 0 [swapper]
> 0 0 7 ffff88102c506080 RU 0.0 0 0 [swapper]
> 0 0 8 ffff88082c016ae0 RU 0.0 0 0 [swapper]
> 0 0 9 ffff88102c506ae0 RU 0.0 0 0 [swapper]
> 0 0 10 ffff88082c05caa0 RU 0.0 0 0 [swapper]
> 0 0 11 ffff88102c507540 RU 0.0 0 0 [swapper]
> 0 0 12 ffff88082c09cae0 RU 0.0 0 0 [swapper]
.....
4926 1 5 ffff880828a38ae0 ?? 0.0 0 0 mingetty
4928 1 1 ffff88102a4e8040 ?? 0.0 0 0 mingetty
4930 1 19 ffff880827af4080 ?? 0.0 0 0 mingetty
4932 1 2 ffff88100f122040 ?? 0.0 0 0 mingetty
4934 1 18 ffff8810296ea080 ?? 0.0 0 0 mingetty
4936 1047 4 ffff880ff342d540 IN 0.0 11184 948 udevd
4937 1047 5 ffff88082a240080 IN 0.0 11184 948 udevd
5060 3772 2 ffff88082881d540 ?? 0.0 0 0 sshd
5078 1 1 ffff88100f060ae0 ?? 0.0 0 0 sshd
5079 1 1 ffff88082b882ae0 ?? 0.0 0 0 bash
如果我取出内核线程（无论如何它们都显示 %MEM 为零），我们可以看到我最后几乎没有运行任何东西：
crash> ps -u
PID PPID CPU TASK ST %MEM VSZ RSS COMM
1 0 1 ffff88082c41b500 ?? 0.0 19348 348 init
1047 1 2 ffff881029524040 IN 0.0 11188 948 udevd
3171 1 3 ffff880826ccaaa0 IN 0.0 27636 240 auditd
3172 1 17 ffff881029d1b500 IN 0.0 27636 240 auditd
> 3772 1 0 ffff88102b257500 RU 0.0 64072 668 sshd
4800 1 0 ffff88100f061540 ?? 0.0 0 0 dsm_om_shrsvcd
4842 1 16 ffff88100f012ae0 ?? 0.0 0 0 cmcld
4854 1 17 ffff88082a241540 ?? 0.0 0 0 cmlogd
4855 1 3 ffff88082796cae0 ?? 0.0 0 0 cmfileassistd
4856 1 18 ffff88082809d500 ?? 0.0 0 0 cmnetd
4860 1 0 ffff88082705aae0 ?? 0.0 0 0 cmresourced
4924 1 9 ffff88102a4e8aa0 ?? 0.0 0 0 mingetty
4926 1 5 ffff880828a38ae0 ?? 0.0 0 0 mingetty
4928 1 1 ffff88102a4e8040 ?? 0.0 0 0 mingetty
4930 1 19 ffff880827af4080 ?? 0.0 0 0 mingetty
4932 1 2 ffff88100f122040 ?? 0.0 0 0 mingetty
4934 1 18 ffff8810296ea080 ?? 0.0 0 0 mingetty
4936 1047 4 ffff880ff342d540 IN 0.0 11184 948 udevd
4937 1047 5 ffff88082a240080 IN 0.0 11184 948 udevd
5060 3772 2 ffff88082881d540 ?? 0.0 0 0 sshd
5078 1 1 ffff88100f060ae0 ?? 0.0 0 0 sshd
5079 1 1 ffff88082b882ae0 ?? 0.0 0 0 bash
5257 1 1 ffff8808279e6aa0 ?? 0.0 0 0 jnx_mlnxsnmp_da
按照 Soham 的建议，包括更多输出。不幸的是，我无法从中得出任何进一步的结论。我能做的最好的事情就是怀疑内核内存泄漏，因为无论如何用户级进程几乎都死了。
crash> ps -G | tail -n +2 | cut -b2- | gawk '{mem += $8} END {print "total " mem/1048576 "GB"}'
total 0.00391006GB
请注意，此时几乎所有用户级进程都已停止，因此预计报告的使用率较低。
内存不足消息：
正如我上面提到的，有 39 条“内存不足：”消息，它们是：
crash> log -m | grep Out
<3>[ 223.556616] Out of memory: Kill process 3189 (portreserve) score 1 or sacrifice child
<3>[ 223.787234] Out of memory: Kill process 3196 (rsyslogd) score 1 or sacrifice child
<3>[ 224.237119] Out of memory: Kill process 3728 (dbus-daemon) score 1 or sacrifice child
<3>[ 228.771770] Out of memory: Kill process 3758 (snmpd) score 1 or sacrifice child
<3>[ 229.033466] Out of memory: Kill process 3782 (xinetd) score 1 or sacrifice child
<3>[ 229.257710] Out of memory: Kill process 3782 (xinetd) score 1 or sacrifice child
<3>[ 229.484321] Out of memory: Kill process 3782 (xinetd) score 1 or sacrifice child
<3>[ 229.711169] Out of memory: Kill process 3782 (xinetd) score 1 or sacrifice child
<3>[ 229.934955] Out of memory: Kill process 3801 (cmproxyd) score 1 or sacrifice child
<3>[ 230.159542] Out of memory: Kill process 3812 (ntpd) score 1 or sacrifice child
<3>[ 230.382083] Out of memory: Kill process 3953 (master) score 1 or sacrifice child
<3>[ 230.606613] Out of memory: Kill process 3953 (master) score 1 or sacrifice child
<3>[ 230.829515] Out of memory: Kill process 3953 (master) score 1 or sacrifice child
<3>[ 230.832105] Out of memory: Kill process 3961 (crond) score 1 or sacrifice child
<3>[ 236.749746] Out of memory: Kill process 3974 (atd) score 1 or sacrifice child
<3>[ 236.969421] Out of memory: Kill process 4272 (dsm_sa_datamgrd) score 1 or sacrifice child
<3>[ 237.192102] Out of memory: Kill process 4492 (dsm_sa_datamgrd) score 1 or sacrifice child
<3>[ 237.746301] Out of memory: Kill process 4552 (dsm_sa_eventmgr) score 1 or sacrifice child
<3>[ 237.968308] Out of memory: Kill process 4613 (dsm_sa_snmpd) score 1 or sacrifice child
<3>[ 238.190550] Out of memory: Kill process 4614 (dsm_sa_snmpd) score 1 or sacrifice child
<3>[ 238.644020] Out of memory: Kill process 4643 (dsm_om_connsvcd) score 1 or sacrifice child
<3>[ 238.865658] Out of memory: Kill process 4643 (dsm_om_connsvcd) score 1 or sacrifice child
<3>[ 251.285450] Out of memory: Kill process 4643 (dsm_om_connsvcd) score 1 or sacrifice child
<3>[ 251.506601] Out of memory: Kill process 4800 (dsm_om_shrsvcd) score 1 or sacrifice child
<3>[ 251.727570] Out of memory: Kill process 4842 (cmcld) score 1 or sacrifice child
<3>[ 251.947085] Out of memory: Kill process 4842 (cmcld) score 1 or sacrifice child
<3>[ 252.167096] Out of memory: Kill process 4854 (cmlogd) score 1 or sacrifice child
<3>[ 252.384090] Out of memory: Kill process 4855 (cmfileassistd) score 1 or sacrifice child
<3>[ 252.603324] Out of memory: Kill process 4924 (mingetty) score 1 or sacrifice child
<3>[ 252.820757] Out of memory: Kill process 4926 (mingetty) score 1 or sacrifice child
<3>[ 253.037558] Out of memory: Kill process 4928 (mingetty) score 1 or sacrifice child
<3>[ 253.254908] Out of memory: Kill process 4930 (mingetty) score 1 or sacrifice child
<3>[ 253.257391] Out of memory: Kill process 4932 (mingetty) score 1 or sacrifice child
<3>[ 253.259357] Out of memory: Kill process 4934 (mingetty) score 1 or sacrifice child
<3>[ 253.261353] Out of memory: Kill process 5060 (sshd) score 1 or sacrifice child
<3>[ 253.263365] Out of memory: Kill process 5060 (sshd) score 1 or sacrifice child
<3>[ 253.264392] Out of memory: Kill process 5079 (bash) score 1 or sacrifice child
<3>[ 253.266352] Out of memory: Kill process 5257 (jnx_mlnxsnmp_da) score 1 or sacrifice child
<0>[ 253.529344] Kernel panic - not syncing: Out of memory and no killable processes...
系统输出：
crash> sys
KERNEL: /usr/lib/debug/lib/modules/2.6.32-279.5.2.el6.x86_64/vmlinux
DUMPFILE: pcdata03.vmcore.flat [PARTIAL DUMP]
CPUS: 32
DATE: Wed Feb 6 02:11:52 2013
UPTIME: 00:04:12
LOAD AVERAGE: 3.03, 0.95, 0.34
TASKS: 578
NODENAME: ....
RELEASE: 2.6.32-279.5.2.el6.x86_64
VERSION: #1 SMP Fri Aug 24 01:07:11 UTC 2012
MACHINE: x86_64 (2700 Mhz)
MEMORY: 64 GB
PANIC: "[ 253.529344] Kernel panic - not syncing: Out of memory and no killable processes..."
kmem -z
crash> kmem -z
NODE: 0 ZONE: 0 ADDR: ffff88000000a0c0 NAME: "DMA"
SIZE: 4095 PRESENT: 3839 MIN/LOW/HIGH: 5/6/7
VM_STAT:
NR_FREE_PAGES: 3936
NR_INACTIVE_ANON: 0
NR_ACTIVE_ANON: 0
NR_INACTIVE_FILE: 0
NR_ACTIVE_FILE: 0
NR_UNEVICTABLE: 0
NR_MLOCK: 0
NR_ANON_PAGES: 0
NR_FILE_MAPPED: 0
NR_FILE_PAGES: 0
NR_FILE_DIRTY: 0
NR_WRITEBACK: 0
NR_SLAB_RECLAIMABLE: 0
NR_SLAB_UNRECLAIMABLE: 0
NR_PAGETABLE: 0
NR_KERNEL_STACK: 0
NR_UNSTABLE_NFS: 0
NR_BOUNCE: 0
NR_VMSCAN_WRITE: 0
NR_VMSCAN_IMMEDIATE: 0
NR_WRITEBACK_TEMP: 0
NR_ISOLATED_ANON: 0
NR_ISOLATED_FILE: 0
NR_SHMEM: 0
NUMA_HIT: 0
NUMA_MISS: 0
NUMA_FOREIGN: 0
NUMA_INTERLEAVE_HIT: 0
NUMA_LOCAL: 0
NUMA_OTHER: 0
NR_ANON_TRANSPARENT_HUGEPAGES: 0
NODE: 0 ZONE: 1 ADDR: ffff880000012780 NAME: "DMA32"
SIZE: 1044480 PRESENT: 756520 MIN/LOW/HIGH: 1030/1287/1545
VM_STAT:
NR_FREE_PAGES: 30117
NR_INACTIVE_ANON: 0
NR_ACTIVE_ANON: 0
NR_INACTIVE_FILE: 1
NR_ACTIVE_FILE: 0
NR_UNEVICTABLE: 0
NR_MLOCK: 0
NR_ANON_PAGES: 0
NR_FILE_MAPPED: 0
NR_FILE_PAGES: 1
NR_FILE_DIRTY: 0
NR_WRITEBACK: 0
NR_SLAB_RECLAIMABLE: 4
NR_SLAB_UNRECLAIMABLE: 4150
NR_PAGETABLE: 0
NR_KERNEL_STACK: 0
NR_UNSTABLE_NFS: 0
NR_BOUNCE: 0
NR_VMSCAN_WRITE: 0
NR_VMSCAN_IMMEDIATE: 0
NR_WRITEBACK_TEMP: 0
NR_ISOLATED_ANON: 0
NR_ISOLATED_FILE: 0
NR_SHMEM: 0
NUMA_HIT: 575606
NUMA_MISS: 3
NUMA_FOREIGN: 0
NUMA_INTERLEAVE_HIT: 0
NUMA_LOCAL: 575598
NUMA_OTHER: 11
NR_ANON_TRANSPARENT_HUGEPAGES: 0
NODE: 0 ZONE: 2 ADDR: ffff88000001ae40 NAME: "Normal"
SIZE: 7602176 PRESENT: 7498240 MIN/LOW/HIGH: 10217/12771/15325
VM_STAT:
NR_FREE_PAGES: 10443
NR_INACTIVE_ANON: 134
NR_ACTIVE_ANON: 197
NR_INACTIVE_FILE: -47
NR_ACTIVE_FILE: 42
NR_UNEVICTABLE: 0
NR_MLOCK: 0
NR_ANON_PAGES: 219
NR_FILE_MAPPED: 115
NR_FILE_PAGES: 45
NR_FILE_DIRTY: 0
NR_WRITEBACK: 0
NR_SLAB_RECLAIMABLE: 908
NR_SLAB_UNRECLAIMABLE: 18771
NR_PAGETABLE: 91
NR_KERNEL_STACK: 556
NR_UNSTABLE_NFS: 0
NR_BOUNCE: 0
NR_VMSCAN_WRITE: 0
NR_VMSCAN_IMMEDIATE: 0
NR_WRITEBACK_TEMP: 0
NR_ISOLATED_ANON: 0
NR_ISOLATED_FILE: 0
NR_SHMEM: 34
NUMA_HIT: 8243991
NUMA_MISS: 648
NUMA_FOREIGN: 4593726
NUMA_INTERLEAVE_HIT: 20066
NUMA_LOCAL: 8243829
NUMA_OTHER: 810
NR_ANON_TRANSPARENT_HUGEPAGES: 0
NODE: 0 ZONE: 3 ADDR: ffff880000023500 NAME: "Movable"
[unpopulated]
NODE: 1 ZONE: 0 ADDR: ffff880840000040 NAME: "DMA"
[unpopulated]
NODE: 1 ZONE: 1 ADDR: ffff880840008700 NAME: "DMA32"
[unpopulated]
NODE: 1 ZONE: 2 ADDR: ffff880840010dc0 NAME: "Normal"
SIZE: 8388608 PRESENT: 8273920 MIN/LOW/HIGH: 11274/14092/16911
VM_STAT:
NR_FREE_PAGES: 10114
NR_INACTIVE_ANON: 417
NR_ACTIVE_ANON: 83
NR_INACTIVE_FILE: 47
NR_ACTIVE_FILE: 32
NR_UNEVICTABLE: 0
NR_MLOCK: 0
NR_ANON_PAGES: 436
NR_FILE_MAPPED: 22
NR_FILE_PAGES: 154
NR_FILE_DIRTY: 0
NR_WRITEBACK: 0
NR_SLAB_RECLAIMABLE: 863
NR_SLAB_UNRECLAIMABLE: 21939
NR_PAGETABLE: 134
NR_KERNEL_STACK: 27
NR_UNSTABLE_NFS: 0
NR_BOUNCE: 0
NR_VMSCAN_WRITE: 3
NR_VMSCAN_IMMEDIATE: 5
NR_WRITEBACK_TEMP: 0
NR_ISOLATED_ANON: 0
NR_ISOLATED_FILE: 23
NR_SHMEM: 20
NUMA_HIT: 4332488
NUMA_MISS: 4593726
NUMA_FOREIGN: 665
NUMA_INTERLEAVE_HIT: 20007
NUMA_LOCAL: 4309300
NUMA_OTHER: 4616914
NR_ANON_TRANSPARENT_HUGEPAGES: 0
NODE: 1 ZONE: 3 ADDR: ffff880840019480 NAME: "Movable"
[unpopulated]
kmem -f
crash> kmem -f
NODE
0
ZONE NAME SIZE FREE MEM_MAP START_PADDR START_MAPNR
0 DMA 4095 3936 ffffea0000000038 1000 0
AREA SIZE FREE_AREA_STRUCT BLOCKS PAGES
0 4k ffff880000012128 2 2
0 4k ffff880000012138 0 0
0 4k ffff880000012148 0 0
0 4k ffff880000012158 0 0
0 4k ffff880000012168 0 0
1 8k ffff880000012180 1 2
1 8k ffff880000012190 0 0
1 8k ffff8800000121a0 0 0
1 8k ffff8800000121b0 0 0
1 8k ffff8800000121c0 0 0
2 16k ffff8800000121d8 1 4
2 16k ffff8800000121e8 0 0
2 16k ffff8800000121f8 0 0
2 16k ffff880000012208 0 0
2 16k ffff880000012218 0 0
3 32k ffff880000012230 1 8
3 32k ffff880000012240 0 0
3 32k ffff880000012250 0 0
3 32k ffff880000012260 0 0
3 32k ffff880000012270 0 0
4 64k ffff880000012288 1 16
4 64k ffff880000012298 0 0
4 64k ffff8800000122a8 0 0
4 64k ffff8800000122b8 0 0
4 64k ffff8800000122c8 0 0
5 128k ffff8800000122e0 0 0
5 128k ffff8800000122f0 0 0
5 128k ffff880000012300 0 0
5 128k ffff880000012310 0 0
5 128k ffff880000012320 0 0
6 256k ffff880000012338 1 64
6 256k ffff880000012348 0 0
6 256k ffff880000012358 0 0
6 256k ffff880000012368 0 0
6 256k ffff880000012378 0 0
7 512k ffff880000012390 0 0
7 512k ffff8800000123a0 0 0
7 512k ffff8800000123b0 0 0
7 512k ffff8800000123c0 0 0
7 512k ffff8800000123d0 0 0
8 1024k ffff8800000123e8 1 256
8 1024k ffff8800000123f8 0 0
8 1024k ffff880000012408 0 0
8 1024k ffff880000012418 0 0
8 1024k ffff880000012428 0 0
9 2048k ffff880000012440 0 0
9 2048k ffff880000012450 0 0
9 2048k ffff880000012460 0 0
9 2048k ffff880000012470 1 512
9 2048k ffff880000012480 0 0
10 4096k ffff880000012498 0 0
10 4096k ffff8800000124a8 0 0
10 4096k ffff8800000124b8 3 3072
10 4096k ffff8800000124c8 0 0
10 4096k ffff8800000124d8 0 0
ZONE NAME SIZE FREE MEM_MAP START_PADDR START_MAPNR
1 DMA32 1044480 30117 ffffea0000038000 1000000 4095
AREA SIZE FREE_AREA_STRUCT BLOCKS PAGES
0 4k ffff88000001a7e8 24 24
0 4k ffff88000001a7f8 4 4
0 4k ffff88000001a808 13 13
0 4k ffff88000001a818 0 0
0 4k ffff88000001a828 0 0
1 8k ffff88000001a840 2 4
1 8k ffff88000001a850 2 4
1 8k ffff88000001a860 4 8
1 8k ffff88000001a870 0 0
1 8k ffff88000001a880 0 0
2 16k ffff88000001a898 0 0
2 16k ffff88000001a8a8 3 12
2 16k ffff88000001a8b8 4 16
2 16k ffff88000001a8c8 0 0
2 16k ffff88000001a8d8 0 0
3 32k ffff88000001a8f0 0 0
3 32k ffff88000001a900 3 24
3 32k ffff88000001a910 3 24
3 32k ffff88000001a920 0 0
3 32k ffff88000001a930 0 0
4 64k ffff88000001a948 1 16
4 64k ffff88000001a958 3 48
4 64k ffff88000001a968 6 96
4 64k ffff88000001a978 0 0
4 64k ffff88000001a988 0 0
5 128k ffff88000001a9a0 0 0
5 128k ffff88000001a9b0 3 96
5 128k ffff88000001a9c0 7 224
5 128k ffff88000001a9d0 0 0
5 128k ffff88000001a9e0 0 0
6 256k ffff88000001a9f8 0 0
6 256k ffff88000001aa08 1 64
6 256k ffff88000001aa18 6 384
6 256k ffff88000001aa28 0 0
6 256k ffff88000001aa38 0 0
7 512k ffff88000001aa50 1 128
7 512k ffff88000001aa60 0 0
7 512k ffff88000001aa70 8 1024
7 512k ffff88000001aa80 0 0
7 512k ffff88000001aa9
小智 8
检查前 20 个最大的物理内存消耗者（常驻集大小）。
crash> ps -G | sed 's/>//g' | sort -k 8,8 -n | awk '$8 ~ /[0-9]/{ $8 = $8/1024" MB"; print }' | tail -20
检查大页面的数量。
crash> p -d nr_huge_pages
$ crash --osrelease vmcore.flat
2.6.32-279.5.2.el6.x86_64
$ rpm2cpio kernel-debug-debuginfo-2.6.32-279.5.2.el6.x86_64.rpm | \
cpio -idv ./usr/lib/debug/lib/modules/*/vmlinux
$ bunzip2 vmcore.flat.bz2
$ crash vmcore.flat ./usr/lib/debug/lib/modules/2.6.32-279.5.2.el6.x86_64/vmlinux
crash> sys
KERNEL: ./usr/lib/debug/lib/modules/2.6.32-279.5.2.el6.x86_64/vmlinux
DUMPFILE: vmcore.flat [PARTIAL DUMP]
CPUS: 32
DATE: Tue Feb 5 12:11:52 2013
UPTIME: 00:04:12
LOAD AVERAGE: 3.03, 0.95, 0.34
TASKS: 578
NODENAME: ...
RELEASE: 2.6.32-279.5.2.el6.x86_64
VERSION: #1 SMP Fri Aug 24 01:07:11 UTC 2012
MACHINE: x86_64 (2700 Mhz)
MEMORY: 64 GB
PANIC: "[ 253.529344] Kernel panic - not syncing: Out of memory and no killable processes..."
a) 由于内存不足而发生恐慌，但系统上禁用了“panic_on_oom”参数。
crash> p -d sysctl_panic_on_oom
sysctl_panic_on_oom = $6 = 0
此参数启用或禁用内存不足时的恐慌功能。如果设置为 0，内核将杀死一些称为 oom_killer 的流氓进程。通常，oom_killer 可以杀死流氓进程，系统会存活下来。如果将其设置为 1，则发生内存不足时内核会发生混乱。
b) 那么，我们是如何在 oom 事件发生时捕获 vmcore 的？
好吧，让我们检查一下 mm/oom_kill.c 源代码。它说如果系统上没有任何东西可以杀死，那么只需挂起或恐慌。
++++++
499 /* Found nothing?!?! Either we hang forever, or we panic. */
500 if (!p) {
501 read_unlock(&tasklist_lock);
502 cpuset_unlock();
503 panic("Out of memory and no killable processes...\n"); <<<------
504 }
505
++++++
所以我们进入了恐慌状态，因为在这个系统上启用了 kdump 服务，vmcore 被捕获。
crash> log
[..]
[ 253.351427] Node 0 DMA free:15744kB min:20kB low:24kB high:28kB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:15356kB mlocked:0kB dirty:0kB writeback:0kB mapped:0kB shmem:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB pagetables:0kB unstable:0kB bounce:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? yes
[ 253.352234] lowmem_reserve[]: 0 2955 32245 32245
[ 253.352812] Node 0 DMA32 free:120436kB min:4120kB low:5148kB high:6180kB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:32kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:3026080kB mlocked:0kB dirty:0kB writeback:0kB mapped:0kB shmem:0kB slab_reclaimable:20kB slab_unreclaimable:16600kB kernel_stack:0kB pagetables:0kB unstable:0kB bounce:0kB writeback_tmp:0kB pages_scanned:1 all_unreclaimable? no
[ 253.353637] lowmem_reserve[]: 0 0 29290 29290
[ 253.354216] Node 0 Normal free:40580kB min:40868kB low:51084kB high:61300kB active_anon:956kB inactive_anon:536kB active_file:260kB inactive_file:0kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:29992960kB mlocked:0kB dirty:0kB writeback:0kB mapped:460kB shmem:136kB slab_reclaimable:3640kB slab_unreclaimable:75128kB kernel_stack:4448kB pagetables:428kB unstable:0kB bounce:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
[ 253.355047] lowmem_reserve[]: 0 0 0 0
[ 253.355624] Node 1 Normal free:39896kB min:45096kB low:56368kB high:67644kB active_anon:412kB inactive_anon:1668kB active_file:288kB inactive_file:0kB unevictable:0kB isolated(anon):0kB isolated(file):220kB present:33095680kB mlocked:0kB dirty:0kB writeback:0kB mapped:92kB shmem:80kB slab_reclaimable:3496kB slab_unreclaimable:87864kB kernel_stack:216kB pagetables:564kB unstable:0kB bounce:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
[ 253.356457] lowmem_reserve[]: 0 0 0 0
[ 253.357034] Node 0 DMA: 2*4kB 1*8kB 1*16kB 1*32kB 1*64kB 0*128kB 1*256kB 0*512kB 1*1024kB 1*2048kB 3*4096kB = 15744kB
[ 253.358351] Node 0 DMA32: 41*4kB 8*8kB 7*16kB 6*32kB 10*64kB 10*128kB 7*256kB 9*512kB 7*1024kB 5*2048kB 23*4096kB = 120468kB
[ 253.359674] Node 0 Normal: 718*4kB 558*8kB 278*16kB 169*32kB 88*64kB 47*128kB 13*256kB 5*512kB 0*1024kB 1*2048kB 1*4096kB = 40872kB
[ 253.360995] Node 1 Normal: 876*4kB 447*8kB 249*16kB 174*32kB 116*64kB 40*128kB 8*256kB 1*512kB 1*1024kB 2*2048kB 1*4096kB = 40952kB
[ 253.362319] 154 total pagecache pages
[ 253.362502] 0 pages in swap cache
[ 253.362684] Swap cache stats: add 0, delete 0, find 0/0
[ 253.362869] Free swap = 0kB
[ 253.363050] Total swap = 0kB
[ 253.526814] 16777215 pages RAM
[ 253.526999] 294628 pages reserved
[ 253.527190] 114911 pages shared
[ 253.527372] 16392561 pages non-shared
[..]
crash> kmem -i
PAGES TOTAL PERCENTAGE
TOTAL MEM 16482587 62.9 GB ---- -------------------------------+
FREE 54610 213.3 MB 0% of TOTAL MEM |
USED 16427977 62.7 GB 99% of TOTAL MEM |
SHARED 4683 18.3 MB 0% of TOTAL MEM |
BUFFERS 118 472 KB 0% of TOTAL MEM |
CACHED 82 328 KB 0% of TOTAL MEM |
SLAB 46635 182.2 MB 0% of TOTAL MEM |
|
TOTAL SWAP 0 0 ---- ----------------------+ |
SWAP USED 0 0 100% of TOTAL SWAP | |
SWAP FREE 0 0 0% of TOTAL SWAP | |
| |
| |
crash> p -d totalram_pages | |
totalram_pages = $5 = 16482587 | |
| |
crash> !echo "scale=5;(16482587*4096)/2^30"|bc -q | |
62.87607 <<<-----[ Total physical memory is 62.9 GB ] <<<--|--------+
|
crash> p -d total_swap_pages |
total_swap_pages = $6 = 0 <<<------[ No Swap on the system ] <<<-----------+
crash> ps -G | tail -n +2 | cut -b2- | gawk '{mem += $8} END {print "total " mem/1048576 "GB"}'
total 0.00391006GB
crash> ps -G | sed 's/>//g' | sort -k 8,8 -n | awk '$8 ~ /[0-9]/{ $8 = $8/1024" MB"; print }' | tail -20
965 2 21 ffff8808292f1500 IN 0.0 0 0 MB [ext4-dio-unwrit]
966 2 22 ffff8808292d4080 IN 0.0 0 0 MB [ext4-dio-unwrit]
967 2 23 ffff8808292ce040 IN 0.0 0 0 MB [ext4-dio-unwrit]
968 2 24 ffff8808299b5540 IN 0.0 0 0 MB [ext4-dio-unwrit]
969 2 25 ffff880829aa6040 IN 0.0 0 0 MB [ext4-dio-unwrit]
970 2 26 ffff880827367500 IN 0.0 0 0 MB [ext4-dio-unwrit]
971 2 27 ffff880827366aa0 IN 0.0 0 0 MB [ext4-dio-unwrit]
972 2 28 ffff880827366040 IN 0.0 0 0 MB [ext4-dio-unwrit]
97 2 23 ffff88082c1ac080 IN 0.0 0 0 MB [ksoftirqd/23]
973 2 29 ffff880827371540 IN 0.0 0 0 MB [ext4-dio-unwrit]
974 2 30 ffff880827370ae0 IN 0.0 0 0 MB [ext4-dio-unwrit]
975 2 31 ffff880827370080 IN 0.0 0 0 MB [ext4-dio-unwrit]
98 2 23 ffff88082c1bb500 IN 0.0 0 0 MB [watchdog/23]
99 2 24 ffff88082c1baaa0 IN 0.0 0 0 MB [migration/24]
3171 1 3 ffff880826ccaaa0 IN 0.0 27636 0.234375 MB auditd
1 0 1 ffff88082c41b500 UN 0.0 19348 0.339844 MB init
3772 1 0 ffff88102b257500 RU 0.0 64072 0.652344 MB sshd
1047 1 2 ffff881029524040 IN 0.0 11188 0.925781 MB udevd
4936 1047 4 ffff880ff342d540 IN 0.0 11184 0.925781 MB udevd
4937 1047 5 ffff88082a240080 IN 0.0 11184 0.925781 MB udevd
crash> p -d sysctl_overcommit_memory
sysctl_overcommit_memory = $7 = 0
此值包含启用内存过量使用的标志。当此标志为 0 时，内核会尝试估计用户空间请求更多内存时剩余的可用内存量。
crash> p -d sysctl_overcommit_ratio
sysctl_overcommit_ratio = $8 = 50
当 overcommit_memory 设置为 2 时，提交的地址空间不允许超过 swap 加上物理 RAM 的这个百分比。
crash> p -d zone_reclaim_mode
zone_reclaim_mode = $4 = 0
Zone_reclaim_mode 允许某人设置或多或少激进的方法来在区域内存不足时回收内存。如果设置为零，则不会发生区域回收。
crash> p -d min_free_kbytes
min_free_kbytes = $3 = 90112 <<<--------[ 88 MB ]
在整个系统中保持空闲的最小千字节数。该值用于计算每个低内存区域的水印值，然后分配一些与其大小成比例的保留空闲页面。设置此参数时，因为太低和太高的值都会造成损害。
换句话说，设置min_free_kbytes得太低会阻止系统回收内存。这可能会导致系统挂起和 OOM 杀死多个进程。但是，将此参数设置为过高的值（总系统内存的 5-10%）将导致您的系统立即内存不足。Linux 旨在使用所有可用 RAM 来缓存文件系统数据。设置较高的 min_free_kbytes 值会导致系统花费太多时间来回收内存。
上面参数的值看起来没问题，那么我的记忆在哪里？？？
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