对于linux主机，如果没有足够的内存来执行其他任务，会抛出OOM，随后系统会开始杀死进程以释放内存，凡是运行在宿主机的进程都有可能被kill，包括docker及其他程序，如果重要的进程被kill，与他相关的服务都会down。
在抛出了OOM的时候，系统会为每个进程计算出一个分数，分数高的进程会优先被kill掉，计算分数有一下3个指标：
/proc/PID/oom_score_adj #这是一个-1000到1000的值，如果值为-1000，则该进程永远不会被kill
/proc/PID/oom_ajd #这是一个-17到+15的值，如果值为-17则表示不能被kill，该参数是为了和旧版本linux内核兼容
/proc/PID/oom_score #这个值时系统综合进程的内存消耗量、CPU时间（utime+stime）、存货时间（uptime-start time）和omm_adj计算出的进程得分，消耗内存越多得分越高
实验环节：
先介绍一个重要的工具—-docker-stress-ng，后面我们用它来模拟容器占用资源的情况。
root@docker1:/home/z9999# docker run -it --rm lorel/docker-stress-ng --help
Unable to find image 'lorel/docker-stress-ng:latest' locally
latest: Pulling from lorel/docker-stress-ng
Image docker.io/lorel/docker-stress-ng:latest uses outdated schema1 manifest format. Please upgrade to a schema2 image for better future compatibility. More information at https://docs.docker.com/registry/spec/deprecated-schema-v1/
c52e3ed763ff: Pull complete
a3ed95caeb02: Pull complete
7f831269c70e: Pull complete
Digest: sha256:c8776b750869e274b340f8e8eb9a7d8fb2472edd5b25ff5b7d55728bca681322
Status: Downloaded newer image for lorel/docker-stress-ng:latest
stress-ng, version 0.03.11
Usage: stress-ng [OPTION [ARG]]
--h, --help show help
--affinity N start N workers that rapidly change CPU affinity
--affinity-ops N stop when N affinity bogo operations completed
--affinity-rand change affinity randomly rather than sequentially
--aio N start N workers that issue async I/O requests
--aio-ops N stop when N bogo async I/O requests completed
--aio-requests N number of async I/O requests per worker
-a N, --all N start N workers of each stress test
-b N, --backoff N wait of N microseconds before work starts
-B N, --bigheap N start N workers that grow the heap using calloc()
--bigheap-ops N stop when N bogo bigheap operations completed
--bigheap-growth N grow heap by N bytes per iteration
--brk N start N workers performing rapid brk calls
--brk-ops N stop when N brk bogo operations completed
--brk-notouch don't touch (page in) new data segment page
--bsearch start N workers that exercise a binary search
--bsearch-ops stop when N binary search bogo operations completed
--bsearch-size number of 32 bit integers to bsearch
-C N, --cache N start N CPU cache thrashing workers
--cache-ops N stop when N cache bogo operations completed (x86 only)
--cache-flush flush cache after every memory write (x86 only)
--cache-fence serialize stores
--class name specify a class of stressors, use with --sequential
--chmod N start N workers thrashing chmod file mode bits
--chmod-ops N stop chmod workers after N bogo operations
-c N, --cpu N start N workers spinning on sqrt(rand())
--cpu-ops N stop when N cpu bogo operations completed
-l P, --cpu-load P load CPU by P %%, 0=sleep, 100=full load (see -c)
--cpu-method m specify stress cpu method m, default is all
-D N, --dentry N start N dentry thrashing processes
--dentry-ops N stop when N dentry bogo operations completed
--dentry-order O specify dentry unlink order (reverse, forward, stride)
--dentries N create N dentries per iteration
--dir N start N directory thrashing processes
--dir-ops N stop when N directory bogo operations completed
-n, --dry-run do not run
--dup N start N workers exercising dup/close
--dup-ops N stop when N dup/close bogo operations completed
--epoll N start N workers doing epoll handled socket activity
--epoll-ops N stop when N epoll bogo operations completed
--epoll-port P use socket ports P upwards
--epoll-domain D specify socket domain, default is unix
--eventfd N start N workers stressing eventfd read/writes
--eventfd-ops N stop eventfd workers after N bogo operations
--fault N start N workers producing page faults
--fault-ops N stop when N page fault bogo operations completed
--fifo N start N workers exercising fifo I/O
--fifo-ops N stop when N fifo bogo operations completed
--fifo-readers N number of fifo reader processes to start
--flock N start N workers locking a single file
--flock-ops N stop when N flock bogo operations completed
-f N, --fork N start N workers spinning on fork() and exit()
--fork-ops N stop when N fork bogo operations completed
--fork-max P create P processes per iteration, default is 1
--fstat N start N workers exercising fstat on files
--fstat-ops N stop when N fstat bogo operations completed
--fstat-dir path fstat files in the specified directory
--futex N start N workers exercising a fast mutex
--futex-ops N stop when N fast mutex bogo operations completed
--get N start N workers exercising the get*() system calls
--get-ops N stop when N get bogo operations completed
-d N, --hdd N start N workers spinning on write()/unlink()
--hdd-ops N stop when N hdd bogo operations completed
--hdd-bytes N write N bytes per hdd worker (default is 1GB)
--hdd-direct minimize cache effects of the I/O
--hdd-dsync equivalent to a write followed by fdatasync
--hdd-noatime do not update the file last access time
--hdd-sync equivalent to a write followed by fsync
--hdd-write-size N set the default write size to N bytes
--hsearch start N workers that exercise a hash table search
--hsearch-ops stop when N hash search bogo operations completed
--hsearch-size number of integers to insert into hash table
--inotify N start N workers exercising inotify events
--inotify-ops N stop inotify workers after N bogo operations
-i N, --io N start N workers spinning on sync()
--io-ops N stop when N io bogo operations completed
--ionice-class C specify ionice class (idle, besteffort, realtime)
--ionice-level L specify ionice level (0 max, 7 min)
-k, --keep-name keep stress process names to be 'stress-ng'
--kill N start N workers killing with SIGUSR1
--kill-ops N stop when N kill bogo operations completed
--lease N start N workers holding and breaking a lease
--lease-ops N stop when N lease bogo operations completed
--lease-breakers N number of lease breaking processes to start
--link N start N workers creating hard links
--link-ops N stop when N link bogo operations completed
--lsearch start N workers that exercise a linear search
--lsearch-ops stop when N linear search bogo operations completed
--lsearch-size number of 32 bit integers to lsearch
-M, --metrics print pseudo metrics of activity
--metrics-brief enable metrics and only show non-zero results
--memcpy N start N workers performing memory copies
--memcpy-ops N stop when N memcpy bogo operations completed
--mmap N start N workers stressing mmap and munmap
--mmap-ops N stop when N mmap bogo operations completed
--mmap-async using asynchronous msyncs for file based mmap
--mmap-bytes N mmap and munmap N bytes for each stress iteration
--mmap-file mmap onto a file using synchronous msyncs
--mmap-mprotect enable mmap mprotect stressing
--msg N start N workers passing messages using System V messages
--msg-ops N stop msg workers after N bogo messages completed
--mq N start N workers passing messages using POSIX messages
--mq-ops N stop mq workers after N bogo messages completed
--mq-size N specify the size of the POSIX message queue
--nice N start N workers that randomly re-adjust nice levels
--nice-ops N stop when N nice bogo operations completed
--no-madvise don't use random madvise options for each mmap
--null N start N workers writing to /dev/null
--null-ops N stop when N /dev/null bogo write operations completed
-o, --open N start N workers exercising open/close
--open-ops N stop when N open/close bogo operations completed
-p N, --pipe N start N workers exercising pipe I/O
--pipe-ops N stop when N pipe I/O bogo operations completed
-P N, --poll N start N workers exercising zero timeout polling
--poll-ops N stop when N poll bogo operations completed
--procfs N start N workers reading portions of /proc
--procfs-ops N stop procfs workers after N bogo read operations
--pthread N start N workers that create multiple threads
--pthread-ops N stop pthread workers after N bogo threads created
--pthread-max P create P threads at a time by each worker
-Q, --qsort N start N workers exercising qsort on 32 bit random integers
--qsort-ops N stop when N qsort bogo operations completed
--qsort-size N number of 32 bit integers to sort
-q, --quiet quiet output
-r, --random N start N random workers
--rdrand N start N workers exercising rdrand instruction (x86 only)
--rdrand-ops N stop when N rdrand bogo operations completed
-R, --rename N start N workers exercising file renames
--rename-ops N stop when N rename bogo operations completed
--sched type set scheduler type
--sched-prio N set scheduler priority level N
--seek N start N workers performing random seek r/w IO
--seek-ops N stop when N seek bogo operations completed
--seek-size N length of file to do random I/O upon
--sem N start N workers doing semaphore operations
--sem-ops N stop when N semaphore bogo operations completed
--sem-procs N number of processes to start per worker
--sendfile N start N workers exercising sendfile
--sendfile-ops N stop after N bogo sendfile operations
--sendfile-size N size of data to be sent with sendfile
--sequential N run all stressors one by one, invoking N of them
--sigfd N start N workers reading signals via signalfd reads
--sigfd-ops N stop when N bogo signalfd reads completed
--sigfpe N start N workers generating floating point math faults
--sigfpe-ops N stop when N bogo floating point math faults completed
--sigsegv N start N workers generating segmentation faults
--sigsegv-ops N stop when N bogo segmentation faults completed
-S N, --sock N start N workers doing socket activity
--sock-ops N stop when N socket bogo operations completed
--sock-port P use socket ports P to P + number of workers - 1
--sock-domain D specify socket domain, default is ipv4
--stack N start N workers generating stack overflows
--stack-ops N stop when N bogo stack overflows completed
-s N, --switch N start N workers doing rapid context switches
--switch-ops N stop when N context switch bogo operations completed
--symlink N start N workers creating symbolic links
--symlink-ops N stop when N symbolic link bogo operations completed
--sysinfo N start N workers reading system information
--sysinfo-ops N stop when sysinfo bogo operations completed
-t N, --timeout N timeout after N seconds
-T N, --timer N start N workers producing timer events
--timer-ops N stop when N timer bogo events completed
--timer-freq F run timer(s) at F Hz, range 1000 to 1000000000
--tsearch start N workers that exercise a tree search
--tsearch-ops stop when N tree search bogo operations completed
--tsearch-size number of 32 bit integers to tsearch
--times show run time summary at end of the run
-u N, --urandom N start N workers reading /dev/urandom
--urandom-ops N stop when N urandom bogo read operations completed
--utime N start N workers updating file timestamps
--utime-ops N stop after N utime bogo operations completed
--utime-fsync force utime meta data sync to the file system
-v, --verbose verbose output
--verify verify results (not available on all tests)
-V, --version show version
-m N, --vm N start N workers spinning on anonymous mmap
--vm-bytes N allocate N bytes per vm worker (default 256MB)
--vm-hang N sleep N seconds before freeing memory
--vm-keep redirty memory instead of reallocating
--vm-ops N stop when N vm bogo operations completed
--vm-locked lock the pages of the mapped region into memory
--vm-method m specify stress vm method m, default is all
--vm-populate populate (prefault) page tables for a mapping
--wait N start N workers waiting on child being stop/resumed
--wait-ops N stop when N bogo wait operations completed
--zero N start N workers reading /dev/zero
--zero-ops N stop when N /dev/zero bogo read operations completed
Example: stress-ng --cpu 8 --io 4 --vm 2 --vm-bytes 128M --fork 4 --timeout 10s
Note: Sizes can be suffixed with B,K,M,G and times with s,m,h,d,y
–oom-score-adj=-1000~1000 为容器设定一个oom-score-adj的分值
-m,–memory #b\k\m\g 限制最大可用内存
这张图片中我给docker-stress-ng加了–vm 5 –vm-bytes 1g ，也就是启动5个work，每个work使用1G内存，并没有对容器做任何限制，宿主机内存马上就被占满了，并且系统严重卡顿，还抛出了oom，一直在kill进程
这次加上了-m 512m 限制最多使用512m内存
–memory-reservation #b\k\m\g 软限制
–memory-swap #b\k\m\g | 0 | unset | -1
这个选项需要和-m使用，且必须大于-m的值，实际可分配的swap大小为–memory-swap的值减去-m的值
如果等于-m的值，容器无权限访问swap
如果为0则忽略该设置，并将该值视为未设置，即未设置交换分区。
如果设置为unset，如果宿主机开启了swap，则实际容器的swap值为2x( –memory)，即两倍于物理内存大小，但是并不准确(在容器中使用free命令所看到的swap空间并不精确，毕竟每个容器都可以看到具体大小，但是宿主机的swap是有上限而且不是所有容器看到的累计大小)。
如果设置为-1，如果宿主机开启了swap，则容器可以使用主机上swap的最大空间。
–memory-swappiness 设置使用swap的倾向性
–cpus 限制可用cpu数量，1为100%，2为200%，0.5为50%
这张图片中我给docker-stress-ng加了–vm 2 –cpu2 ，也就是启动2个work，每个work使用2个（200%）cpu，并没有对容器做任何限制，宿主机CPU马上就被占满了 
这次加上–cpus参数试试
-c, –cpu-shares CPU共享值
–cpuset-cpus CPU亲和性绑定，写CPU编号，多个CPU用逗号隔开
原文地址：http://www.cnblogs.com/z9999/p/16832862.html
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