核心结构体 oom_control，主要记录事发现场。
主要的入口为 out_of_memory，调用着有三个
mmecontrol:mem_cgroup_out_of_memory: 用户程序分配内存的时候，经过 cgroup 的检查mem_cgroup_charge没有通过。page_alloc.c:__alloc_pages_may_oom: 在此处失败，是因为不受 cgroup 管理的用户进程分配内存失败。sysrq:moom_callback: 通过 sudo echo f > /proc/sysrq-trigger 手动触发
- 为什么会因为 cpuset 而 oom ？
struct oom_control {
/* Used to determine cpuset */
struct zonelist *zonelist;因为该进程运行执行的 node 上没有内存了。
- reaper 是做啥的?
在 oom_kill_process 中，将那些已经被杀死进程持有的内存直接释放掉1。
因为 vm.oom_kill_allocating_task 为 0 的时候，内核需要扫描所有的进程，这个过程非常的缓慢。
static void dump_header(struct oom_control *oc, struct task_struct *p)- dump_unreclaimable_slab
__show_mem- 整个系统的信息
- 每一个 Node / zone 的信息
- zone 中 buddy 的信息
- dump_tasks : 取决于是否在 cgroup 中，打印每一个 process 的信息，其中
- total_vm : 所有映射的虚拟地址空间
- rss : 映射的物理页面数量
- dump_oom_summary
- 当前的上下文，cpuset 等
[ 112.939900] Out of memory: Killed process 5515 (a.out) total-vm:22022692kB, anon-rss:10875852kB, file-rss:1336kB, shmem-rss:0kB, UID:0 pgtables:41296kB oom_score_adj:0
[ 113.314803] oom_reaper: reaped process 5515 (a.out), now anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
[ 130.772276] a.out invoked oom-killer: gfp_mask=0x100cca(GFP_HIGHUSER_MOVABLE), order=0, oom_score_adj=0
[ 130.773033] CPU: 17 PID: 5532 Comm: a.out Kdump: loaded Not tainted 5.10.0-60.18.0.50.oe2203.x86_64 #1
[ 130.773692] Hardware name: Martins3 Inc Hacking Alpine, BIOS 12 2022-2-2
[ 130.774184] Call Trace:
[ 130.774403] dump_stack+0x57/0x6a
[ 130.774676] dump_header+0x4a/0x1f0
[ 130.774954] oom_kill_process.cold+0xb/0x10
[ 130.775276] out_of_memory+0x100/0x310
[ 130.775569] __alloc_pages+0xe78/0xf50
[ 130.775866] pagecache_get_page+0x1cc/0x380
[ 130.776188] filemap_fault+0x2f1/0x510
[ 130.776494] ext4_filemap_fault+0x2d/0x40 [ext4]
[ 130.776850] __do_fault+0x38/0x110
[ 130.777122] do_read_fault+0x31/0xc0
[ 130.777405] do_fault+0x71/0x150
[ 130.777667] __handle_mm_fault+0x3dd/0x6d0
[ 130.777983] ? _copy_from_user+0x3c/0x80
[ 130.778287] handle_mm_fault+0xbe/0x290
[ 130.778586] exc_page_fault+0x273/0x550
[ 130.778887] ? asm_exc_page_fault+0x8/0x30
[ 130.779546] asm_exc_page_fault+0x1e/0x30
[ 130.779872] RIP: 0033:0x4011cb
[ 130.780126] Code: Unable to access opcode bytes at RIP 0x4011a1.
[ 130.780557] RSP: 002b:00007ffdb61e5780 EFLAGS: 00010206
[ 130.780944] RAX: 00007f48aad81000 RBX: 0000000000000000 RCX: 00007f4b41007887
[ 130.781455] RDX: 00007f4880f08000 RSI: 0000000000000001 RDI: 00007f4b410fd570
[ 130.781969] RBP: 00007ffdb61e57a0 R08: 00007f4b410fd570 R09: 000000000000000b
[ 130.782482] R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffdb61e58b8
[ 130.782997] R13: 0000000000401142 R14: 0000000000403e08 R15: 00007f4b41150000
[ 130.783519] Mem-Info:
[ 130.783726] active_anon:285 inactive_anon:2820935 isolated_anon:0
active_file:28 inactive_file:59 isolated_file:0
unevictable:2873 dirty:29 writeback:0
slab_reclaimable:8117 slab_unreclaimable:18581
mapped:2936 shmem:2213 pagetables:6126 bounce:0
free:40346 free_pcp:62 free_cma:0
[ 130.786048] Node 0 active_anon:1140kB inactive_anon:11283740kB active_file:112kB inactive_file:236kB unevictable:11492kB isolated(anon):0kB isolated(file):0kB mapped:11744kB dirty:116kB writeback:0kB shmem:8852kB shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 10727424kB writeback_tmp:0kB kernel_stack:6896kB all_unreclaimable? yes
[ 130.787958] Node 0 DMA free:13296kB min:144kB low:180kB high:216kB reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:15992kB managed:15360kB mlocked:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
[ 130.789699] lowmem_reserve[]: 0 2412 11403 11403 11403
[ 130.790083] Node 0 DMA32 free:59900kB min:24044kB low:30052kB high:36060kB reserved_highatomic:0KB active_anon:0kB inactive_anon:2439692kB active_file:172kB inactive_file:84kB unevictable:0kB writepending:0kB present:3129204kB managed:2503388kB mlocked:0kB pagetables:80kB bounce:0kB free_pcp:248kB local_pcp:248kB free_cma:0kB
[ 130.791976] lowmem_reserve[]: 0 0 8991 8991 8991
[ 130.792325] Node 0 Normal free:88188kB min:88444kB low:110552kB high:132660kB reserved_highatomic:0KB active_anon:1140kB inactive_anon:8843776kB active_file:268kB inactive_file:68kB unevictable:11492kB writepending:116kB present:9437184kB managed:9207308kB mlocked:11492kB pagetables:24424kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
[ 130.794295] lowmem_reserve[]: 0 0 0 0 0
[ 130.794597] Node 0 DMA: 0*4kB 0*8kB 1*16kB (U) 1*32kB (U) 1*64kB (U) 1*128kB (U) 1*256kB (U) 1*512kB (U) 0*1024kB 2*2048kB (UM) 2*4096kB (M) = 13296kB
[ 130.795862] Node 0 DMA32: 14*4kB (UM) 46*8kB (U) 50*16kB (UME) 40*32kB (UE) 31*64kB (UE) 25*128kB (UME) 17*256kB (UME) 17*512kB (UM) 39*1024kB (UME) 0*2048kB 0*4096kB = 60680kB
[ 130.796931] Node 0 Normal: 1371*4kB (UME) 343*8kB (UE) 600*16kB (UE) 394*32kB (UME) 222*64kB (UME) 153*128kB (UME) 60*256kB (UE) 19*512kB (UME) 3*1024kB (U) 0*2048kB 0*4096kB = 92388kB
[ 130.798040] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=1048576kB
[ 130.798654] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
[ 130.799250] 4778 total pagecache pages
[ 130.799543] 0 pages in swap cache
[ 130.799816] Swap cache stats: add 2567968, delete 2567967, find 5630/8293
[ 130.800313] Free swap = 0kB
[ 130.800553] Total swap = 0kB
[ 130.800796] 3145595 pages RAM
[ 130.801042] 0 pages HighMem/MovableOnly
[ 130.801341] 214081 pages reserved
[ 130.801608] 0 pages hwpoisoned
[ 130.801864] Tasks state (memory values in pages):
[ 130.802219] [ pid ] uid tgid total_vm rss pgtables_bytes swapents oom_score_adj name
[ 130.802859] [ 784] 0 784 6662 1221 77824 0 -250 systemd-journal
[ 130.803502] [ 818] 0 818 7430 1714 77824 0 -1000 systemd-udevd
[ 130.804128] [ 964] 32 964 2722 1139 61440 0 0 rpcbind
[ 130.804724] [ 1007] 0 1007 812 27 45056 0 0 mdadm
[ 130.805303] [ 1022] 0 1022 4442 290 49152 0 -1000 auditd
[ 130.805892] [ 1128] 81 1128 2187 770 53248 0 -900 dbus-daemon
[ 130.806504] [ 1133] 997 1133 678 450 45056 0 0 lsmd
[ 130.807084] [ 1137] 0 1137 19916 87 57344 0 -500 irqbalance
[ 130.807694] [ 1141] 987 1141 58815 991 90112 0 0 polkitd
[ 130.808292] [ 1149] 0 1149 77789 1292 110592 0 0 rngd
[ 130.808873] [ 1154] 984 1154 19541 410 61440 0 0 chronyd
[ 130.809464] [ 1157] 0 1157 4193 1177 69632 0 0 systemd-logind
[ 130.810097] [ 1161] 0 1161 3573 739 65536 0 0 systemd-machine
[ 130.810735] [ 1163] 0 1163 2786 939 65536 0 0 restorecond
[ 130.811621] [ 1204] 0 1204 36925 7350 176128 0 0 firewalld
[ 130.812293] [ 1209] 0 1209 86700 1758 151552 0 0 NetworkManager
[ 130.812927] [ 1228] 0 1228 3476 1486 69632 0 -1000 sshd
[ 130.813502] [ 1232] 0 1232 52252 5367 151552 0 0 targetclid
[ 130.814114] [ 1234] 0 1234 69191 3357 143360 0 0 tuned
[ 130.814696] [ 1235] 0 1235 17609 578 90112 0 0 gssproxy
[ 130.815292] [ 1513] 0 1513 2256 922 53248 0 0 dhclient
[ 130.815890] [ 1531] 0 1531 2890 2819 61440 0 -17 iscsid
[ 130.816475] [ 1534] 0 1534 57333 1142 90112 34 0 rsyslogd
[ 130.817073] [ 1574] 0 1574 947 526 45056 0 0 atd
[ 130.817641] [ 1576] 0 1576 5845 686 69632 0 0 crond
[ 130.818219] [ 1582] 0 1582 5435 416 53248 0 0 agetty
[ 130.818803] [ 1584] 0 1584 5341 472 57344 0 0 agetty
[ 130.819387] [ 2033] 992 2033 2188 275 57344 0 0 dnsmasq
[ 130.819979] [ 2034] 0 2034 2181 90 57344 0 0 dnsmasq
[ 130.820565] [ 5259] 0 5259 3970 1603 73728 0 0 sshd
[ 130.821139] [ 5264] 0 5264 4637 1624 77824 0 0 systemd
[ 130.821729] [ 5267] 0 5267 6025 1512 90112 0 0 (sd-pam)
[ 130.822323] [ 5273] 0 5273 21817 597 73728 0 0 gcr-ssh-agent
[ 130.822948] [ 5274] 0 5274 3934 891 73728 0 0 sshd
[ 130.823521] [ 5276] 0 5276 6879 1214 69632 0 0 zsh
[ 130.824089] [ 5406] 0 5406 3970 1597 69632 0 0 sshd
[ 130.824663] [ 5409] 0 5409 3934 908 69632 30 0 sshd
[ 130.825237] [ 5410] 0 5410 6915 1253 69632 0 0 zsh
[ 130.825810] [ 5532] 0 5532 2884233 2793370 22437888 0 0 a.out
[ 130.826389] oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),cpuset=/,mems_allowed=0,global_oom,task_memcg=/user.slice/user-0.slice/session-3.scope,task=a.out,pid=5532,uid=0
[ 130.827731] Out of memory: Killed process 5532 (a.out) total-vm:11536932kB, anon-rss:11172224kB, file-rss:1256kB, shmem-rss:0kB, UID:0 pgtables:21912kB oom_score_adj:0
[ 130.843472] oom_reaper: reaped process 5532 (a.out), now anon-rss:0kB, file-rss:0kB, shmem-rss:0kB没有什么特别惊艳的技术，就是周期性的扫描内核中的一些指标，oomd 比 earlyoom 观测的内容更多。
- psi
- memory.evetns
- cgroup.events : populated
- /proc/$pid/oom_score_adj 可以设置-1000 到 1000，当设置为-1000 时表示不会被 oom killer 选中
- /proc/$pid/oom_adj 它的值从-17 到 15，值越大越容易被 oom killer 选中，值越小表示选中的可能性越小。当值为-17 是，表示该进程永远不会被选中。这个 oom_adj 是要被 oom_score_adj 替代的，只是为了兼容旧的内核版本，暂时保留，以后会被废弃。
- /proc/$pid/oom_score 表示当前进程的 oom 分数
分析下内核的代码:
ONE("oom_score", S_IRUGO, proc_oom_score),
REG("oom_adj", S_IRUGO|S_IWUSR, proc_oom_adj_operations),
REG("oom_score_adj", S_IRUGO|S_IWUSR, proc_oom_score_adj_operations),proc_oom_score_adj_operations 和 proc_oom_adj_operations 都会调用到 __set_oom_adj，两者唯一的区别就是就是做了下数值换算。
如果调整 oom score:
- https://askubuntu.com/questions/60672/how-do-i-use-oom-score-adj
- systemd
- 动态调整
- choom
- Hastening process cleanup with process_mrelease()
- 884a7e5964e06ed93c7771c0d7cf19c09a8946f1
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