Console outputs frequently 'vm_fault: pager read error'

[nykaer]

On console, I'm seeing a lot these:

<SNIP>
vm_fault: pager read error, pid 70868 (rrdtool)
vm_fault: pager read error, pid 70868 (rrdtool)
vm_fault: pager read error, pid 70868 (rrdtool)
vm_fault: pager read error, pid 70868 (rrdtool)
</SNIP>

RRDtool seems to be working fine, and graphs are also working.