On our el6 servers there is a quantity of unused memory while on el5 servers there was no such problem. We need to get more aggressive caching on el6 as it used to be in el5.

Munin graphs on el6:
enter image description here

Munin graphs on el5:

On el6 we try, but dont help:
vm.nr_pdflush_threads = 2
vm.min_free_kbytes = 19921
vm.swappiness = 5
vm.dirty_writeback_centisecs = 2250
vm.dirty_expire_centisecs = 2250
vm.vfs_cache_pressure = 1250

  • You should probably list the version of VMware, the config of the centos5 servers, and so on. – NickW Feb 28 '13 at 10:55
  • 2
    Is there a performance issue on the el6 boxes? – Matt Feb 28 '13 at 10:59
  • Yeah, you seem to be witch-hunting, actually. Lesser RAM usage isn't a problem by itself, is it? – poige Feb 28 '13 at 11:26
  • this is identical dedicated servers Config: 2xE5620 48GB RAM DDR3 HARDWARE RAID10 + BBU (LSI MegaRAID SAS 9260-4i) At first installed centos 5.9 At second installed centos 6.3 Disk activity on el5: i.imgur.com/zPGo4Sv.png On el6: i.imgur.com/4tWBjPV.png Cpu activity on el5: i.imgur.com/n3Z9OoU.png on el6: i.imgur.com/T20eLD8.png – Dmitriy Feb 28 '13 at 12:50
  • But on el5 most unused memory use for cache, and i think this is logical. On all el6 server 30-50% memory unused This is el6 "feature" or we can change cache policy? – Dmitriy Feb 28 '13 at 12:50

These are entirely different operating systems. So behavior on one doesn't necessarily mean the other will show the same characteristics. You have to consider:

  • Different kernel generations...
  • Substantial changes to schedulers.
  • Vastly different compiled-in defaults.
  • sysctl.conf settings are different.
  • Package/application config files are different...
  • Different default filesystems.

The first thing to know about tuning or building an EL6 system is to take advantage of the basic system profile tuning framework. The utility for this is called tuned-adm. Red Hat's documentation is here.

The basic overview of the profiles is:

This may help you eliminate duplicate work as you modify settings. What type of application is running on this system?



echo never > /sys/kernel/mm/redhat_transparent_hugepage/enabled
echo never > /sys/kernel/mm/redhat_transparent_hugepage/defrag

after this:


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