Tugger the SLUGger!SLUG Mailing List Archives

RE: [SLUG] reported memory and actual memory

On Wed, 2007-07-25 at 16:06 +0800, jam@xxxxxxxxx wrote:
> 32 bit machines can't use more than 4G. Bigmem kernels fiddle and go partway 
> but to use more than 4G use 64 bit!

More specifically, the bigmem 32-bit kernel uses PAE to use RAM greater
than 4GB.

The bad news is that this doesn't increase the size of lowmem (a
complicated topic, but basically the memory that can be used for
disk I/O and networking). For some workloads this can be a problem
because of the kernel's tendency to fragment lowmem (eg, backup
servers are prone to this).

That's the reason why it is better to use a 64-bit kernel. Of course,
that has flow-on effects if you use bespoke or binary applications
since you will need to recompile. Also, it can have an effect on
your capacity planning -- 64bit applications usually need 25% more
RAM.  Of course, with as much RAM as you have you might be amply
provisioned with RAM anyway.

 Glen Turner