Quote:
Originally Posted by
MadeInGermany
I hear this over and over again, from the Linux community. Always use 100%, a usage under 100% is wasted RAM, blabla.
This question is asked in the Red Hat forum so there is no doubt the OP is running Linux. The Linux kernel is designed to use all otherwise free RAM as cache with no penalties.
Note that under Unix and Linux, you can't really use 100%, the OS try hard to make sure minfree is left (min_free_kbytes on Linux), although minfree/min_free_kbytes are normally very small compared to the RAM size.
HP-UX might still has an problem freeing buffer cache memory but that's a design issue that should have been fixed if not already. Another System V implementation, Solaris, did it 17 years ago. On Solaris, the cache memory is reported as free memory and is freed almost instantly. See
Understanding Memory Allocation and File System Caching in OpenSolaris (Richard McDougall's Weblog)
On the other hand, RAM allocated in kernel buffers, regardless of the OS, is much more difficult to be retrieved for applications so tuning can be useful here, for example when ZFS is used.
Back to the OP issue, he is running on a virtualized environment and has no access to the hypervisor statistics. The hypervisor might well lie about actual resources available to the kernel so anything is possible.