Dell 2950: 4GB not seen (amd64; works on other 2950:s)

[Derek Ragona]

At 02:48 PM 8/24/2007, Peter Schuller wrote:
>Hello,
>
>I have a Dell 2950 where my 7-CURRENT amd64 FreeBSD does not see all visible
>memory. It has 4 GB of physical RAM. dmesg on boot includes:
>
>usable memory = 4280811520 (4082 MB)
>avail memory  = 4117716992 (3926 MB)
>
>Yet summing memories visible in top yields ~ 2100 MB.
>
>Of note is that I have 6.2/amd64 on several other 2950:s with 4GB of RAM 
>which
>say on boot:
>
>real memory  = 5100273664 (4864 MB)
>avail memory = 4122443776 (3931 MB)
>
>But has all 4 GB visible in top.
>
>Unfortunately I failed to notice this until after the machine has begun being
>used, so I have limited possibilities for rebooting/mucking with BIOS
>settings. I was hoping someone could suggest something right off the bat.
>
>In addition on the problem machine the following sysctl values are present:
>
>hw.physmem: 4280811520
>hw.usermem: 3628220416
>hw.realmem: 5100273664
>hw.cbb.start_memory: 2281701376
>hw.pci.host_mem_start: 2147483648
>
>With hw.usermem being slightly higher (but not 2 GB higher) on the 6.2 system
>without a problem:
>
>hw.physmem: 4283285504
>hw.usermem: 3998797824
>hw.realmem: 5100273664
>hw.cbb.start_memory: 2281701376
>hw.pci.host_mem_start: 2147483648
>
>I was under the impression that memory visibility issues were a thing of the
>past on amd64. Any insight?
>
>Thanks!
>
>--
>/ Peter Schuller

You need to look closely at the hardware configuration for these servers 
and their motherboards.  Often some memory is reserved for things like 
onboard video, etc.  You can free up that video memory by adding a separate 
video card, but necessarily other memory that may be used by the 
motherboard.  Unfortunately with dell systems same model's don't 
necessarily mean same motherboard.  Also, how memory is used via the BIOS 
is dependent on the BIOS version.  You should try to be sure all systems 
you want to compare have the same motherboard and chipset and that these 
also have the same BIOS version.

         -Derek



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