Re: why my systems never cache more than ~900 MB?

[Christoph Lameter <cl@linux-foundation.org>]

On Tue, 24 Mar 2009, Tomasz Chmielewski wrote:

> Christoph Lameter schrieb:
> > On Tue, 24 Mar 2009, Tomasz Chmielewski wrote:
> >
> > > Nick Piggin schrieb:
> > > Does not help me, as what interests me here on these machines is mainly
> > > caching block device data; they are iSCSI targets and access block devices
> > > directly.
> >
> > You can run a 64 bit kernel on those machines. 64 bit kernels can use
> > 32 bit userspace without a problem. Just install an additional kernel and
> > try booting your existing setup with it.
> >
> > > What split should I choose to enable blockdev mapping on the whole memory
> > > on
> > > 32 bit system with 3 or 4 GB RAM? Is it possible with 4 GB RAM at all?
> >
> > A 64 bit kernel will do the trick.
>
> This hardware has problems booting 64 bit kernels (read: CPUs come from the
> 32-bit land).

Then the 1G/3G separation (VMSPLIT_1G) is the best you can do. Will use up
to 3G for low mem. Be aware that your I/O device must support DMA to full
32 bit addresses. If this is an old 32 bit machine with limitations on the
use of bit 31 then the box may have issues.

Put as much as you can into Highmem. Set HIGHMEM4G, HIGHPTE

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