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云服务器 ECS Linux CentOS7 修改 kdump 使用内存

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测试环境:CentOS Linux release 7.0.1406 (Core) ,CentOS Linux release 7.2.1511 (Core) 

配置:CPU 1核, 内存4G

注:版本不同,变化的大小也有差异;内存越大变化越明显。

修改前配置前内存使用情况如下

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<ol class="linenums">
  
 <li class="L0"><span class="pun">[</span><span class="pln">root@test</span><span class="pun">-</span><span class="lit">1</span><span class="pln"> </span><span class="pun">~]#</span><span class="pln"> dmesg </span><span class="pun">|</span><span class="pln"> grep </span><span class="typ">Memory</span></li>
  
 <li class="L1"><span class="pun">[</span><span class="pln">    </span><span class="lit">0.000000</span><span class="pun">]</span><span class="pln"> </span><span class="typ">Memory</span><span class="pun">:</span><span class="pln"> </span><span class="lit">3865640k</span><span class="pun">/</span><span class="lit">4456448k</span><span class="pln"> available </span><span class="pun">(</span><span class="lit">6108k</span><span class="pln"> kernel code</span><span class="pun">,</span><span class="pln"> </span><span class="lit">262536k</span><span class="pln"> absent</span><span class="pun">,</span><span class="pln"> </span><span class="lit">328272k</span><span class="pln"> reserved</span><span class="pun">,</span><span class="pln"> </span><span class="lit">4071k</span><span class="pln"> data</span><span class="pun">,</span><span class="pln"> </span><span class="lit">1584k</span><span class="pln"> init</span><span class="pun">)</span></li>
  
 <li class="L2"><span class="pun">[</span><span class="pln">root@test</span><span class="pun">-</span><span class="lit">1</span><span class="pln"> </span><span class="pun">~]#</span><span class="pln"> free </span><span class="pun">-</span><span class="pln">m</span></li>
  
 <li class="L3"><span class="pln">             total       used       free     shared    buffers     cached</span></li>
  
 <li class="L4"><span class="typ">Mem</span><span class="pun">:</span><span class="pln">          </span><span class="lit">3535</span><span class="pln">        </span><span class="lit">165</span><span class="pln">       </span><span class="lit">3369</span><span class="pln">          </span><span class="lit">8</span><span class="pln">         </span><span class="lit">11</span><span class="pln">         </span><span class="lit">77</span></li>
  
 <li class="L5"><span class="pun">-</span><span class="str">/+ buffers/</span><span class="pln">cache</span><span class="pun">:</span><span class="pln">         </span><span class="lit">76</span><span class="pln">       </span><span class="lit">3459</span></li>
  
 <li class="L6"><span class="typ">Swap</span><span class="pun">:</span><span class="pln">            </span><span class="lit">0</span><span class="pln">          </span><span class="lit">0</span><span class="pln">          </span><span class="lit">0</span></li>
  
 <li class="L7"><span class="pun">[</span><span class="pln">root@test</span><span class="pun">-</span><span class="lit">1</span><span class="pln"> </span><span class="pun">~]#</span><span class="pln"> </span></li>
 
</ol>

修改前配置如下

/boot/grub2/grub.cfg的配置情况如下图crashkernel=auto

运行以下命令修改/boot/grub2/grub.cfg配置文件。

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<ol class="linenums">
  
 <li class="L0"><span class="pln">sudo cp </span><span class="pun">-</span><span class="pln">p </span><span class="pun">/</span><span class="pln">etc</span><span class="pun">/</span><span class="kwd">default</span><span class="pun">/</span><span class="pln">grub </span><span class="pun">/</span><span class="pln">etc</span><span class="pun">/</span><span class="kwd">default</span><span class="pun">/</span><span class="pln">grub</span><span class="pun">.</span><span class="pln">original </span><span class="com">#备份grub文件</span></li>
  
 <li class="L1"><span class="pln">sudo sed </span><span class="pun">--</span><span class="kwd">in</span><span class="pun">-</span><span class="pln">place </span><span class="str">'s/crashkernel=auto /crashkernel=0M /'</span><span class="pln"> </span><span class="pun">/</span><span class="pln">etc</span><span class="pun">/</span><span class="kwd">default</span><span class="pun">/</span><span class="pln">grub </span><span class="com">#设置crashkernel=0M</span></li>
  
 <li class="L2"><span class="pln">sudo grub2</span><span class="pun">-</span><span class="pln">mkconfig </span><span class="pun">-</span><span class="pln">o </span><span class="pun">/</span><span class="pln">boot</span><span class="pun">/</span><span class="pln">grub2</span><span class="pun">/</span><span class="pln">grub</span><span class="pun">.</span><span class="pln">cfg </span><span class="com">#根据上述配置生成新的grub.cfg文件</span></li>
 
</ol>


修改后配置如下

/boot/grub2/grub.cfg的配置情况如下图 crashkernel=0M

修改前配置后内存使用情况如下

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<ol class="linenums">
  
 <li class="L0"><span class="pun">[</span><span class="pln">root@test</span><span class="pun">-</span><span class="lit">1</span><span class="pln"> </span><span class="pun">~]#</span><span class="pln"> free </span><span class="pun">-</span><span class="pln">m</span></li>
  
 <li class="L1"><span class="pln">             total       used       free     shared    buffers     cached</span></li>
  
 <li class="L2"><span class="typ">Mem</span><span class="pun">:</span><span class="pln">          </span><span class="lit">3696</span><span class="pln">        </span><span class="lit">158</span><span class="pln">       </span><span class="lit">3538</span><span class="pln">          </span><span class="lit">8</span><span class="pln">         </span><span class="lit">11</span><span class="pln">         </span><span class="lit">72</span></li>
  
 <li class="L3"><span class="pun">-</span><span class="str">/+ buffers/</span><span class="pln">cache</span><span class="pun">:</span><span class="pln">         </span><span class="lit">74</span><span class="pln">       </span><span class="lit">3621</span></li>
  
 <li class="L4"><span class="typ">Swap</span><span class="pun">:</span><span class="pln">            </span><span class="lit">0</span><span class="pln">          </span><span class="lit">0</span><span class="pln">          </span><span class="lit">0</span></li>
  
 <li class="L5"><span class="pun">[</span><span class="pln">root@test</span><span class="pun">-</span><span class="lit">1</span><span class="pln"> </span><span class="pun">~]#</span><span class="pln">  dmesg </span><span class="pun">|</span><span class="pln"> grep </span><span class="typ">Memory</span></li>
  
 <li class="L6"><span class="pun">[</span><span class="pln">    </span><span class="lit">0.000000</span><span class="pun">]</span><span class="pln"> </span><span class="typ">Memory</span><span class="pun">:</span><span class="pln"> </span><span class="lit">4030504k</span><span class="pun">/</span><span class="lit">4456448k</span><span class="pln"> available </span><span class="pun">(</span><span class="lit">6108k</span><span class="pln"> kernel code</span><span class="pun">,</span><span class="pln"> </span><span class="lit">262536k</span><span class="pln"> absent</span><span class="pun">,</span><span class="pln"> </span><span class="lit">163408k</span><span class="pln"> reserved</span><span class="pun">,</span><span class="pln"> </span><span class="lit">4071k</span><span class="pln"> data</span><span class="pun">,</span><span class="pln"> </span><span class="lit">1584k</span><span class="pln"> init</span><span class="pun">)</span></li>
  
 <li class="L7"><span class="pun">[</span><span class="pln">root@test</span><span class="pun">-</span><span class="lit">1</span><span class="pln"> </span><span class="pun">~]#</span><span class="pln"> </span></li>
 
</ol>

通过对比可以看出

1、free -m 命令中total显示的总大小

修改前为3535M,修改后为3696M,变大了161M

2、 dmesg | grep Memory命令显示

系统保留reserved 减少了对应的大小修改前为328272k,修改后为163408k,减少了164864k,大小为161M

 

通过这样子配置后得到影响:

  • 可用总内存稍有增大
  • 设置crashkernel=0M后,kdump无法正常工作。

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