Linux下谁在消耗我们的cache

拼搏现实的明天。 2022-07-16 14:17 193阅读 0赞

转自：[http://blog.yufeng.info/archives/688][http_blog.yufeng.info_archives_688]

Linux下对文件的访问和设备的访问通常会被cache起来加快访问速度，这个是系统的默认行为。 而cache需要耗费我们的内存，虽然这个内存最后可以通过echo 3>/proc/sys/vm/drop\_caches这样的命令来主动释放。但是有时候我们还是需要理解谁消耗了我们的内存。

我们来先了解下内存的使用情况:

[![free][]][free 1]

[view source][]

[print][] [?][Link 1]

<table> 
 <tbody> 
  <tr> 
   <td><code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>total&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; used&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </code><code><span style="color: #ff1493;">free</span></code>&nbsp;&nbsp;&nbsp;&nbsp; <code>shared&nbsp;&nbsp;&nbsp; buffers&nbsp;&nbsp;&nbsp;&nbsp; cached </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>-/+ buffers/cache:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 87372&nbsp;&nbsp; 24589464 </code></td> 
  </tr> 
 </tbody> 
</table>

有了伟大的systemtap, 我们可以用stap脚本来了解谁在消耗我们的cache了：

[view source][]

[print][] [?][Link 1]

<table> 
 <tbody> 
  <tr> 
   <td><code><span style="color: #008200;">#这个命令行用来调查谁在加数据入page_cache </span></code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>[root@my031045 ~]</code><code><span style="color: #008200;"># stap -e 'probe vfs.add_to_page_cache {printf("dev=%d, devname=%s, ino=%d, index=%d, nrpages=%d/n", dev, devname, ino, index, nrpages )}' </span></code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=2, devname=N/A, ino=0, index=2975, nrpages=1777 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=2, devname=N/A, ino=0, index=3399, nrpages=2594 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=2, devname=N/A, ino=0, index=3034, nrpages=1778 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=2, devname=N/A, ino=0, index=3618, nrpages=2595 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=2, devname=N/A, ino=0, index=1694, nrpages=106 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=2, devname=N/A, ino=0, index=1703, nrpages=107 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=2, devname=N/A, ino=0, index=1810, nrpages=210 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=2, devname=N/A, ino=0, index=1812, nrpages=211 </code></td> 
  </tr> 
 </tbody> 
</table>

这时候我们拷贝个大文件：

[view source][]

[print][] [?][Link 1]

<table> 
 <tbody> 
  <tr> 
   <td><code>[chuba@my031045 ~]$ </code><code><span style="color: #ff1493;">cp</span></code> <code>huge_foo.</code><code><span style="color: #ff1493;">file</span></code>&nbsp; <code>bar </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code><span style="color: #008200;">#这时候我们可以看到文件的内容被猛的添加到cache去： </span></code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=8388614, devname=sda6, ino=2399271, index=39393, nrpages=39393 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=8388614, devname=sda6, ino=2399271, index=39394, nrpages=39394 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=8388614, devname=sda6, ino=2399271, index=39395, nrpages=39395 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=8388614, devname=sda6, ino=2399271, index=39396, nrpages=39396 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=8388614, devname=sda6, ino=2399271, index=39397, nrpages=39397 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=8388614, devname=sda6, ino=2399271, index=39398, nrpages=39398 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=8388614, devname=sda6, ino=2399271, index=39399, nrpages=39399 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=8388614, devname=sda6, ino=2399271, index=39400, nrpages=39400 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=8388614, devname=sda6, ino=2399271, index=39401, nrpages=39401 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=8388614, devname=sda6, ino=2399271, index=39402, nrpages=39402 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=8388614, devname=sda6, ino=2399271, index=39403, nrpages=39403 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=8388614, devname=sda6, ino=2399271, index=39404, nrpages=39404 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=8388614, devname=sda6, ino=2399271, index=39405, nrpages=39405 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=8388614, devname=sda6, ino=2399271, index=39406, nrpages=39406 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=8388614, devname=sda6, ino=2399271, index=39407, nrpages=39407 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=8388614, devname=sda6, ino=2399271, index=39408, nrpages=39408 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=8388614, devname=sda6, ino=2399271, index=39409, nrpages=39409 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=8388614, devname=sda6, ino=2399271, index=39410, nrpages=39410 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>dev=8388614, devname=sda6, ino=2399271, index=39411, nrpages=39411 </code></td> 
  </tr> 
 </tbody> 
</table>

此外加入我们想了解下系统的cache都谁在用呢, 那个文件用到多少页了呢？  
我们有个脚本可以做到，这里非常谢谢 **子团** 让我使用他的代码。

[view source][]

[print][] [?][Link 1]

<table> 
 <tbody> 
  <tr> 
   <td><code>[chuba@my031045 ~]</code><code><span style="color: #008200;"># stap -g viewcache.stp </span></code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>在另外的shell里面 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>[chuba@my031045 ~]</code><code><span style="color: #008200;"># dmesg </span></code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>inode: 116397109, num: 5 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>inode: 116397111, num: 2 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>inode: 116397112, num: 1 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>inode: 116397149, num: 2 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>inode: 116397152, num: 1 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>inode: 116397336, num: 2 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>inode: 116397343, num: 1 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>inode: 116397371, num: 4 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>inode: 116397372, num: 2 </code></td> 
  </tr> 
 </tbody> 
</table>

非常清楚的看出来每个inode占用了多少页，用工具转换下就知道哪个文件耗费了多少内存。

[点击下载viewcache.stp][viewcache.stp]

另外小TIPS：

从inode到文件名的转换  
find / -inum your\_inode

从文件名到inode的转换  
stat -c “%i” your\_filename  
或者 ls -i your\_filename

我们套用了下就马上知道那个文件占用的cache很多。

[view source][]

[print][] [?][Link 1]

<table> 
 <tbody> 
  <tr> 
   <td><code>[chuba@my031045 ~]$ </code><code><span style="color: #ff1493;">sudo</span></code> <code><span style="color: #ff1493;">find</span></code> <code>/ -inum 2399248 </code></td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td><code>/home/chuba/kernel-debuginfo-2.6.18-164.el5.x86_64.rpm</code></td> 
  </tr> 
 </tbody> 
</table>

玩的开心。

参考资料:  
page cache和buffer cache的区别:  
这篇文章总结的最靠谱: [http://blog.chinaunix.net/u/1595/showart.php?id=2209511][http_blog.chinaunix.net_u_1595_showart.php_id_2209511]

后记:  
linux下有个这样的系统调用可以知道页面的状态:mincore – determine whether pages are resident in memory  
同时有人作个脚本[fincore][]更方便大家的使用, [点击下载fincore][fincore 1]

后来子团告诉我还有这个工具: [https://code.google.com/p/linux-ftools/][https_code.google.com_p_linux-ftools]

[http_blog.yufeng.info_archives_688]: http://blog.yufeng.info/archives/688
[free]: /images/20220709/d668347355194466bc2843ece6eeba5c.png
[free 1]: http://blog.yufeng.info/wp-content/uploads/2010/09/free.jpg
[view source]: http://writeblog.csdn.net/#viewSource
[print]: http://writeblog.csdn.net/#printSource
[Link 1]: http://writeblog.csdn.net/#about
[viewcache.stp]: http://blog.yufeng.info/wp-content/uploads/2010/09/viewcache.stp_.txt
[http_blog.chinaunix.net_u_1595_showart.php_id_2209511]: http://blog.chinaunix.net/u/1595/showart.php?id=2209511
[fincore]: http://net.doit.wisc.edu/~plonka/fincore/
[fincore 1]: http://blog.yufeng.info/wp-content/uploads/2010/09/fincore.txt
[https_code.google.com_p_linux-ftools]: https://code.google.com/p/linux-ftools/