Out of memory, OOM killer输出信息分析

当out of memory发生时，out_of_memory函数会选择一个内核认为犯有分配过多内存 “罪行”的进程，并杀死该进程。

这就有很大的几率腾出较多的空闲页，然后再跳转回重试内存分配的操作。

这里我们不讨论out_of_memory 函数流程 选择要牺牲进程的策略方法。

我们仅讨论out of memory发生时，内核输出信息的含义。

1. OOM 信息

以下是一段典型的out of memory 内核输出信息：

<4>[12345.342532] systemd-journal invoked oom-killer: gfp_mask=0x800d0, order=0, oom_score_adj=0
<4>[12345.351216] CPU: 1 PID: 1371 Comm: systemd-journal Tainted: G           O 3.14.31-00017-g40fab71 #1
<4>[12345.360695] Backtrace:
<4>[12345.363263] [<c0012fcc>] (dump_backtrace) from [<c00131a4>] (show_stack+0x20/0x24)
<4>[12345.371192]  r6:00000000 r5:ffffffff r4:00000000 r3:bd943631
<4>[12345.377136] [<c0013184>] (show_stack) from [<c07bbe78>] (dump_stack+0x7c/0xc8)
<4>[12345.384710] [<c07bbdfc>] (dump_stack) from [<c07ba7e4>] (dump_header.isra.14+0x74/0x188)
<4>[12345.393184]  r6:000800d0 r5:00000000 r4:e8088000 r3:00000002
<4>[12345.399126] [<c07ba770>] (dump_header.isra.14) from [<c00f8a28>] (oom_kill_process+0x230/0x3e0)
<4>[12345.408234]  r10:00000000 r8:000800d0 r7:00000000 r6:c0b89aa8 r5:000800d0 r4:e9bb79c0
<4>[12345.416462] [<c00f87f8>] (oom_kill_process) from [<c00f90c8>] (out_of_memory+0x2f4/0x354)
<4>[12345.425024]  r10:00000000 r9:00000000 r8:000800d0 r7:00000000 r6:c0b89aa8 r5:c0b89d08
<4>[12345.433249]  r4:c0b89aa8
<4>[12345.435903] [<c00f8dd4>] (out_of_memory) from [<c00fd6c8>] (__alloc_pages_nodemask+0x93c/0x988)
<4>[12345.445011]  r10:00000000 r9:c0c38fc0 r8:c0b871d8 r7:e8088000 r6:c0c39bc0 r5:00000000
<4>[12345.453234]  r4:000800d0
<4>[12345.455887] [<c00fcd8c>] (__alloc_pages_nodemask) from [<c00fd734>] (__get_free_pages+0x20/0x3c)
<4>[12345.465087]  r10:e97d36a8 r9:00000063 r8:e8089f6c r7:00000063 r6:b6f79f68 r5:e97d36a8
<4>[12345.473311]  r4:00000000
<4>[12345.475965] [<c00fd714>] (__get_free_pages) from [<c0196878>] (proc_pid_readlink+0x68/0x110)
<4>[12345.484808] [<c0196810>] (proc_pid_readlink) from [<c013dcb8>] (SyS_readlinkat+0xf0/0x104)
<4>[12345.493461]  r7:bea40520 r6:ffffff9c r5:00004000 r4:00000000
<4>[12345.499402] [<c013dbc8>] (SyS_readlinkat) from [<c000eee0>] (ret_fast_syscall+0x0/0x34)
<4>[12345.507785]  r10:00000000 r9:e8088000 r8:c000f148 r7:0000014c r6:00000063 r5:b6f79f68
<4>[12345.516011]  r4:00000064
<4>[12345.518663] Mem-info:
<4>[12345.521049] Normal per-cpu:
<4>[12345.523969] CPU    0: hi:   42, btch:   7 usd:  23
<4>[12345.528979] CPU    1: hi:   42, btch:   7 usd:  25
<4>[12345.534004] HighMem per-cpu:
<4>[12345.537013] CPU    0: hi:  186, btch:  31 usd:  27
<4>[12345.542199] CPU    1: hi:  186, btch:  31 usd:  29
<4>[12345.547247] active_anon:21860 inactive_anon:14790 isolated_anon:0
<4>[12345.547247]  active_file:41585 inactive_file:10422 isolated_file:0
<4>[12345.547247]  unevictable:0 dirty:9 writeback:205 unstable:0
<4>[12345.547247]  free:285748 slab_reclaimable:2100 slab_unreclaimable:26286
<4>[12345.547247]  mapped:26079 shmem:14857 pagetables:687 bounce:0
<4>[12345.547247]  free_cma:57779
<4>[12345.581839] Normal free:233460kB min:2488kB low:3108kB high:3732kB active_anon:17312kB 
inactive_anon:10824kB active_file:128kB inactive_file:4kB unevictable:0kB isolated(anon):0kB 
isolated(file):0kB present:774144kB managed:387568kB mlocked:0kB dirty:16kB writeback:76kB 
mapped:3296kB shmem:10840kB slab_reclaimable:8400kB slab_unreclaimable:105144kB kernel_stack:1168kB 
pagetables:2748kB unstable:0kB bounce:0kB free_cma:231116kB writeback_tmp:0kB pages_scanned:1648 
all_unreclaimable? yes
<4>[12345.627014] lowmem_reserve[]: 0 10168 10168
<4>[12345.631565] HighMem free:909036kB