title: vm/min_free_kbytes - Why Keep Minimum Reserved Memory?
body: <p>According to this <a href="http://doc.opensuse.org/products/draft/SLES/SLES-tuning_sd_draft/cha.tuning.memory.html" rel="noreferrer">article</a>: </p>
  
  <blockquote>
    <p>/proc/sys/vm/min_free_kbytes: This controls the amount of memory that is kept free for use by special reserves including “atomic” allocations (those which cannot wait for reclaim)</p>
  </blockquote>
  
  <p>My question is that what does it mean by "those which cannot wait for reclaim"? In other words, I would like to understand why there's a need to tell the system to always keep a certain minimum amount of memory free and under what circumstances will this memory be used? [It must be used by something; don't see the need otherwise]</p>
  
  <p>My second question: does setting this memory to something higher than 4MB (on my system) leads to better performance? We have a server which occasionally exhibit very poor shell performance (e.g. ls -l takes 10-15 seconds to execute) when certain processes get going and if setting this number to something higher will lead to better shell performance?</p>