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I am having trouble running e2fsck due to memory limitations, as detailed in this question. In the course of investigating that, I came upon something that may be of more general interest, so I will put it in its own question.

While running e2fsck, memory usage on the machine goes to around 99%. There also starts to be some swapping. What is odd, however, is that this is the start of the output of top -M:

top - 14:09:37 up 1 day,  4:14,  3 users,  load average: 1.00, 1.00, 0.92
Tasks: 127 total,   2 running, 125 sleeping,   0 stopped,   0 zombie
Cpu(s): 12.4%us,  1.8%sy,  0.0%ni, 81.1%id,  4.6%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:  1004.961M total,  987.484M used,   17.477M free,  664.469M buffers
Swap:   21.953G total,   72.574M used,   21.882G free,   68.512M cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                                                                                                                                         
 7627 root      20   0  164m 152m  61m R 100.0 15.2  49:18.25 e2fsck                                                                                                                                                                                                          
 8340 root      20   0  2696  996  752 R  2.0  0.1   0:00.01 top                                                                                                                                                                                                              
    1 root      20   0  2896    8    4 S  0.0  0.0   0:01.87 init

So even though overall memory usage is at 99%, e2fsck is only showing as using 15.2%, and there are no other memory hogs running.

Where did all the memory go? Is this behavior unique to e2fsck, or is this "normal" (not desirable, but understandable). I don't know how memory can be used by anything other than a running process.

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marked as duplicate by voretaq7 Feb 27 '13 at 1:22

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

It's desirable. If the memory were free, it would be no better than if you didn't have the memory at all. Free memory is wasted memory. If you're thinking "I want it free now so I can use it later", forget it. You can use it now and use it later. – David Schwartz Feb 26 '13 at 23:30
up vote 1 down vote accepted

This is normal. Linux uses free memory to buffer disk access.

See Why is Linux reporting "free" memory strangely?

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Cool, thanks for the link. – WinnieNicklaus Feb 26 '13 at 22:21

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