尽管有大量可用内存,是否会调用 OOM 杀手?

尽管有大量可用内存,是否会调用 OOM 杀手?

我有一台服务器,自两周前以来,几乎每晚都会调用一次或两次 OOM 杀手。服务器应该有足够的内存可以释放(缓存/缓冲区,inactive_file见下文)以及足够的可用交换空间,但我无法理解内核打印的数字。我在互联网上读过很多关于这个问题的帖子,我很清楚打印的数字意味着什么free,但我就是无法分析这个特定问题。

以下是更多信息:

  • 它是一个虚拟机(Ubuntu 16.04),Ubuntu 的内核是 4.4.0-59-generic。
  • 主机是VMware ESXi 6.5。
  • VM 通过 lxc 运行多个容器。因此进程数可能相当高。
  • 该虚拟机已分配 28 GB 内存,并使用约 20 GB 的额外交换文件。

为什么要调用 OOM 杀手?我能做什么(除了盲目地增加更多内存之外 — 我想了解这些数字是否以及为什么实际上表明增加内存会有所帮助)?

以下是上次调用 OOM killer 时的内核消息:

Feb 01 00:37:02 akira kernel: php invoked oom-killer: gfp_mask=0x26000c0, order=2, oom_score_adj=0
Feb 01 00:37:02 akira kernel: php cpuset=lakota mems_allowed=0
Feb 01 00:37:02 akira kernel: CPU: 1 PID: 31693 Comm: php Not tainted 4.4.0-59-generic #80-Ubuntu
Feb 01 00:37:02 akira kernel: Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 04/05/2016
Feb 01 00:37:02 akira kernel:  0000000000000286 00000000eaaf82b8 ffff88052d9afaf0 ffffffff813f7583
Feb 01 00:37:02 akira kernel:  ffff88052d9afcc8 ffff88071bf9aa00 ffff88052d9afb60 ffffffff8120ad5e
Feb 01 00:37:02 akira kernel:  ffff88073fd1a870 ffff88073fd1a860 ffffea000419f440 0000000100000001
Feb 01 00:37:02 akira kernel: Call Trace:
Feb 01 00:37:02 akira kernel:  [<ffffffff813f7583>] dump_stack+0x63/0x90
Feb 01 00:37:02 akira kernel:  [<ffffffff8120ad5e>] dump_header+0x5a/0x1c5
Feb 01 00:37:02 akira kernel:  [<ffffffff81192722>] oom_kill_process+0x202/0x3c0
Feb 01 00:37:02 akira kernel:  [<ffffffff81192b49>] out_of_memory+0x219/0x460
Feb 01 00:37:02 akira kernel:  [<ffffffff81198abd>] __alloc_pages_slowpath.constprop.88+0x8fd/0xa70
Feb 01 00:37:02 akira kernel:  [<ffffffff81198eb6>] __alloc_pages_nodemask+0x286/0x2a0
Feb 01 00:37:02 akira kernel:  [<ffffffff81198f6b>] alloc_kmem_pages_node+0x4b/0xc0
Feb 01 00:37:02 akira kernel:  [<ffffffff8107ea5e>] copy_process+0x1be/0x1b70
Feb 01 00:37:02 akira kernel:  [<ffffffff81391bcc>] ? apparmor_file_alloc_security+0x5c/0x220
Feb 01 00:37:02 akira kernel:  [<ffffffff811ed05a>] ? kmem_cache_alloc+0x1ca/0x1f0
Feb 01 00:37:02 akira kernel:  [<ffffffff81347bd3>] ? security_file_alloc+0x33/0x50
Feb 01 00:37:02 akira kernel:  [<ffffffff810805a0>] _do_fork+0x80/0x360
Feb 01 00:37:02 akira kernel:  [<ffffffff81080929>] SyS_clone+0x19/0x20
Feb 01 00:37:02 akira kernel:  [<ffffffff818384f2>] entry_SYSCALL_64_fastpath+0x16/0x71
Feb 01 00:37:02 akira kernel: Mem-Info:
Feb 01 00:37:02 akira kernel: active_anon:939644 inactive_anon:396161 isolated_anon:0
                               active_file:1683401 inactive_file:3767879 isolated_file:0
                               unevictable:1481 dirty:902 writeback:0 unstable:0
                               slab_reclaimable:155382 slab_unreclaimable:15433
                               mapped:71733 shmem:15843 pagetables:19280 bounce:0
                               free:196889 free_pcp:19 free_cma:0
Feb 01 00:37:02 akira kernel: Node 0 DMA free:15900kB min:36kB low:44kB high:52kB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:15992kB managed:15908kB mlocked:0kB dirty:0kB writeback:0kB mapped:0kB shmem:0kB slab_reclaimable:0kB slab_unreclaimable:8kB kernel_stack:0kB pagetables:0kB unstable:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? yes
Feb 01 00:37:02 akira kernel: lowmem_reserve[]: 0 2940 28091 28091 28091
Feb 01 00:37:02 akira kernel: Node 0 DMA32 free:121140kB min:7068kB low:8832kB high:10600kB active_anon:284776kB inactive_anon:330268kB active_file:701204kB inactive_file:1373280kB unevictable:1828kB isolated(anon):0kB isolated(file):0kB present:3129280kB managed:3048656kB mlocked:1828kB dirty:276kB writeback:0kB mapped:36756kB shmem:4548kB slab_reclaimable:212192kB slab_unreclaimable:5196kB kernel_stack:1056kB pagetables:7168kB unstable:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
Feb 01 00:37:02 akira kernel: lowmem_reserve[]: 0 0 25150 25150 25150
Feb 01 00:37:02 akira kernel: Node 0 Normal free:650516kB min:60476kB low:75592kB high:90712kB active_anon:3473800kB inactive_anon:1254376kB active_file:6032400kB inactive_file:13698236kB unevictable:4096kB isolated(anon):0kB isolated(file):0kB present:26214400kB managed:25754528kB mlocked:4096kB dirty:3332kB writeback:0kB mapped:250176kB shmem:58824kB slab_reclaimable:409336kB slab_unreclaimable:56528kB kernel_stack:9296kB pagetables:69952kB unstable:0kB bounce:0kB free_pcp:72kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
Feb 01 00:37:02 akira kernel: lowmem_reserve[]: 0 0 0 0 0
Feb 01 00:37:02 akira kernel: Node 0 DMA: 1*4kB (U) 1*8kB (U) 1*16kB (U) 0*32kB 2*64kB (U) 1*128kB (U) 1*256kB (U) 0*512kB 1*1024kB (U) 1*2048kB (M) 3*4096kB (M) = 15900kB
Feb 01 00:37:02 akira kernel: Node 0 DMA32: 20703*4kB (UME) 4794*8kB (UME) 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 121164kB
Feb 01 00:37:02 akira kernel: Node 0 Normal: 146130*4kB (UMEH) 7997*8kB (UMEH) 3*16kB (H) 3*32kB (H) 3*64kB (H) 3*128kB (H) 3*256kB (H) 1*512kB (H) 0*1024kB 0*2048kB 0*4096kB = 650496kB
Feb 01 00:37:02 akira kernel: Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
Feb 01 00:37:02 akira kernel: 5489461 total pagecache pages
Feb 01 00:37:02 akira kernel: 21519 pages in swap cache
Feb 01 00:37:02 akira kernel: Swap cache stats: add 390089, delete 368570, find 24240772/24285246
Feb 01 00:37:02 akira kernel: Free swap  = 22195940kB
Feb 01 00:37:02 akira kernel: Total swap = 23064572kB
Feb 01 00:37:02 akira kernel: 7339918 pages RAM
Feb 01 00:37:02 akira kernel: 0 pages HighMem/MovableOnly
Feb 01 00:37:02 akira kernel: 135145 pages reserved
Feb 01 00:37:02 akira kernel: 0 pages cma reserved
Feb 01 00:37:02 akira kernel: 0 pages hwpoisoned
… (snip process list) …
Feb 01 00:37:02 akira kernel: Out of memory: Kill process 12508 (mysqld) score 51 or sacrifice child
Feb 01 00:37:02 akira kernel: Killed process 12508 (mysqld) total-vm:3794008kB, anon-rss:2625732kB, file-rss:5980kB

我还记录了/proc/meminfo每分钟的各种值。以下是从午夜到凌晨 01:00 的图表:

来自 /proc/meminfo 的值
(来源:bunkus.org

输出systctl -a | grep '^vm'

vm.admin_reserve_kbytes = 8192
vm.block_dump = 0
vm.compact_unevictable_allowed = 1
vm.dirty_background_bytes = 0
vm.dirty_background_ratio = 10
vm.dirty_bytes = 0
vm.dirty_expire_centisecs = 3000
vm.dirty_ratio = 20
vm.dirty_writeback_centisecs = 500
vm.dirtytime_expire_seconds = 43200
vm.drop_caches = 0
vm.extfrag_threshold = 500
vm.hugepages_treat_as_movable = 0
vm.hugetlb_shm_group = 0
vm.laptop_mode = 0
vm.legacy_va_layout = 0
vm.lowmem_reserve_ratio = 256   256     32      1
vm.max_map_count = 65530
vm.memory_failure_early_kill = 0
vm.memory_failure_recovery = 1
vm.min_free_kbytes = 67584
vm.min_slab_ratio = 5
vm.min_unmapped_ratio = 1
vm.mmap_min_addr = 65536
vm.nr_hugepages = 0
vm.nr_hugepages_mempolicy = 0
vm.nr_overcommit_hugepages = 0
vm.nr_pdflush_threads = 0
vm.numa_zonelist_order = default
vm.oom_dump_tasks = 1
vm.oom_kill_allocating_task = 0
vm.overcommit_kbytes = 0
vm.overcommit_memory = 0
vm.overcommit_ratio = 50
vm.page-cluster = 3
vm.panic_on_oom = 0
vm.percpu_pagelist_fraction = 0
vm.stat_interval = 1
vm.swappiness = 60
vm.user_reserve_kbytes = 131072
vm.vfs_cache_pressure = 10000
vm.zone_reclaim_mode = 0

谢谢!

答案1

只有当内存耗尽到系统即将崩溃的程度时,内核才会开始终止任务。它不会撒谎。一定有事情正在发生,消耗着你所有的可用 RAM 和交换空间。PHP 和 MySQL 参与其中的事实非常可疑,因为这两个应用程序的资源消耗可能非常动态。内核终止了 mysql,因为它确定它是当前使用中最大的内存消耗者。如果我不得不猜测的话,我会怀疑有人正在对你的 PHP 应用程序运行一个大型查询。

您可以使用它来记录与 Web 服务器的连接iptables,这可能有助于确定谁整晚都在连接您的服务器以及连接频率。它可能会发现可疑 IP 地址整晚都在第 7 层上工作,并启动了数以百万计的 mysql/apache 进程。这种类型的日志记录可能会占用大量磁盘空间,因此不要无限期地打开它。当然,您可能需要根据您的设置调整规则在输入链上的位置。

iptables -A INPUT -p tcp -m state --state NEW -m multiport --dports 80,443 -j LOG --log-prefix "WEB_CLIENT: "

就我个人而言,我会从一个简单的修复开始,将交换增加到 28G 以匹配可用 RAM。Ubuntu 说24G 系统(接近您的系统)的最大交换为 48G:

对于更现代的系统 (>1GB),您的交换空间应至少等于您的物理内存 (RAM) 大小(如果您使用休眠模式),否则您需要的最小值为 round(sqrt(RAM)),最大为 RAM 的两倍。交换空间大于实际使用量的唯一缺点是您将为其保留磁盘空间。

值得一试。如果它有任何变化,你可能需要添加更多物理 RAM。

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