[TriLUG] Growing OS cache in RAM causing high system CPU usage

[Bill Farrow]

On Tue, Jul 8, 2014 at 1:07 PM, Michael Peters
<michael00peters at gmail.com> wrote:

> It's used up all of it's "free" RAM, but ~2/3 of the RAM in use is
> actually OS cache which should just
> seemlessly transfer over to applications that request it right?

This process is "seamless" to your application but there is still
going to be a CPU overhead involved here. The memory pages being used
for OS cache need to be flushed from the CPU caches, and then possibly
written out to disk if they are dirty (have changes in them). Then
they need to be marked as unused and the OS table/list/hash etc needs
to be updated accordingly.

Once the memory is "unused", it probably has to be initialized to zero
before being handed to the application to prevent data leakage.

So it is not CPU "free" even if it is seamless to your application.

Bill