top shows only half of realmem?

[John Baldwin]

On Wednesday, January 26, 2011 8:20:28 am Bartosz Stec wrote:
> W dniu 2011-01-26 14:06, John Baldwin pisze:
> > On Wednesday, January 26, 2011 7:20:34 am Bartosz Stec wrote:
> >> Guys,
> >>
> >> could someone explain me this?
> >>
> >>      # sysctl hw.realmem
> >>      hw.realmem: 2139029504
> >>
> >> top line shows:
> >>
> >>      Mem: 32M Active, 35M Inact, 899M Wired, 8392K Cache, 199M Buf, 58M Free
> >>
> >> 32+35+899+8+199+58 = 1231MB
> >>
> >> Shouldn't that sum to all available ram? Or maybe I'm reading it wrong?
> >> This machine has indeed 2GB of ram on board and showed in BIOS.
> >> i386  FreeBSD 8.2-PRERELEASE #16: Mon Jan 17 22:28:53 CET 2011
> >> Cheers.
> > First, don't include 'buf' as isn't a separate set of RAM, it is only a range
> > of the virtual address space in the kernel.  It used to be relevant when the
> > buffer cache was separate from the VM page cache, but now it is mostly
> > irrelevant (arguably it should just be dropped from top output).
> 
> Thanks for the explanation. So 1231MB - 199MB Buf and we got about 1GB 
> of memory instead of 2B.
> 
> > However, look at what hw.physmem says (and the realmem and availmem lines in
> > dmesg).  realmem is actually not that useful as it is not a count of the
> > amount of memory, but the address of the highest memory page available.  There
> > can be less memory available than that due to "holes" in the address space for
> > PCI memory BARs, etc.
> >
> OK, here you go:
> # sysctl hw | grep mem
> 
>     hw.physmem: 2125893632
>     hw.usermem: 1212100608
>     hw.realmem: 2139029504
>     hw.pci.host_mem_start: 2147483648

Humm, you should still have 2GB of RAM then.  All the memory you set aside
for ARC should be counted in the 'wired' count, so I'm not sure why you see
1GB of RAM rather than 2GB.

-- 
John Baldwin