sysctl修改内核参数 重启不生效

Posted 2022-11-30 ygtff

现象

• 在尝试解决VM hung死问题时，需要修改内核参数 vm.dirty_ratio, 所以就遇到了在/etc/sysctl.conf中修改后，直接sysctl -p，参数修改OK：
  
• 但是，重启机器后，这些参数又是默认值，并没有生效：
  

问题分析解决

• Google发现tuned服务会动态调整系统参数的，那么如果我设置的参数被动态调整了所以不生效。
  所以，我们现在看看tuned配置中有没有修改上面提到的参数：
  

  [root@ceph2 lib]# cd /usr/lib/tuned/ [root@ceph2 tuned]# grep "vm.dirty_ratio" * -R latency-performance/tuned.conf:vm.dirty_ratio=10 throughput-performance/tuned.conf:vm.dirty_ratio = 40 virtual-guest/tuned.conf:vm.dirty_ratio = 30

  
  

• 有3处覆盖sysctl.conf中的参数:

  • 我们来看看virtual-guest/tuned.conf:

    # # tuned configuration # [main] include=throughput-performance [sysctl] # If a workload mostly uses anonymous memory and it hits this limit, the entire # working set is buffered for I/O, and any more write buffering would require # swapping, so it's time to throttle writes until I/O can catch up. Workloads # that mostly use file mappings may be able to use even higher values. # # The generator of dirty data starts writeback at this percentage (system default # is 20%) vm.dirty_ratio = 30 # Filesystem I/O is usually much more efficient than swapping, so try to keep # swapping low. It's usually safe to go even lower than this on systems with # server-grade storage. vm.swappiness = 30

    
    

  • 在main域中，先加载了throught-performance，从字面来看就是提高吞吐性能的：

    # # tuned configuration # [cpu] governor=performance energy_perf_bias=performance min_perf_pct=100 [disk] readahead=>4096 [sysctl] # ktune sysctl settings for rhel6 servers, maximizing i/o throughput # # Minimal preemption granularity for CPU-bound tasks: # (default: 1 msec# (1 + ilog(ncpus)), units: nanoseconds) kernel.sched_min_granularity_ns = 10000000 # SCHED_OTHER wake-up granularity. # (default: 1 msec# (1 + ilog(ncpus)), units: nanoseconds) # # This option delays the preemption effects of decoupled workloads # and reduces their over-scheduling. Synchronous workloads will still # have immediate wakeup/sleep latencies. kernel.sched_wakeup_granularity_ns = 15000000 # If a workload mostly uses anonymous memory and it hits this limit, the entire # working set is buffered for I/O, and any more write buffering would require # swapping, so it's time to throttle writes until I/O can catch up. Workloads # that mostly use file mappings may be able to use even higher values. # # The generator of dirty data starts writeback at this percentage (system default # is 20%) vm.dirty_ratio = 40 # Start background writeback (via writeback threads) at this percentage (system # default is 10%) vm.dirty_background_ratio = 10 # PID allocation wrap value. When the kernel's next PID value # reaches this value, it wraps back to a minimum PID value. # PIDs of value pid_max or larger are not allocated. # # A suggested value for pid_max is 1024 * <# of cpu cores/threads in system> # e.g., a box with 32 cpus, the default of 32768 is reasonable, for 64 cpus, # 65536, for 4096 cpus, 4194304 (which is the upper limit possible). #kernel.pid_max = 65536 # The swappiness parameter controls the tendency of the kernel to move # processes out of physical memory and onto the swap disk. # 0 tells the kernel to avoid swapping processes out of physical memory # for as long as possible # 100 tells the kernel to aggressively swap processes out of physical memory # and move them to swap cache vm.swappiness=10

     

• 所以要想让vm.dirty_ratio这个参数成为我们想要的10，可以通过以下方法解决：
  • 在sysctl.conf中添加vm.dirty_ratio参数，并禁止tuned服务启动。
  • 直接在tuned.conf中修改vm.dirty_ratio参数
  • 在sysctl.conf中添加vm.dirty_ratio参数，然后在rc.local中增加sysctl -p使其生效
    

链接

http://ssdxiao.github.io/linux/2017/03/20/Sysctl-not-applay-on-boot.html