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**mlau** · 19 April 2008, 01:02 AM

Does the BIOS offer an option to remap parts of memory beyond the 4GB line?
The last GB is usually used to map peripheral devices and by the kernel for internal purposes;
any actual RAM there is lost unless BIOS/Chipset are able to remap parts of it.

**oblivious_maximus** · 19 April 2008, 03:37 AM

The BIOS version depicted in the manual has an option called "Memory Hole Remapping" but the current BIOS version (which I'm using) does not. The closest thing is "DCT Unganged Mode", which is enabled. When I tried disabling it, even more memory disappeared - about 3100MB is all that showed up with free then.

**Moustacha** · 19 April 2008, 04:30 AM

I believe it has something to do with the kernel reserving memory for itself. I got 4GB running 64-bit Gutsy and get around what you're getting, 3954. With 1GB you'll notice you're missing memory, giving you about 1011MB.

**oblivious_maximus** · 19 April 2008, 04:40 AM

that's about what my fileserver with an Athlon XP and 1GB of ram shows (1012mb). I was happily going along thinking that my desktop's memory discrepancy was similar, but hwinfo's output (3GB + 768MB) really seems to indicate it's something else...

Does your mtrr account for all 4GB of your memory Moustacha?

edit: I borrowed a 1GB dimm for a few mintues to see if hwinfo would report all 5GB. It did, but I haven't the foggiest what that means given what it shows with 4GB. Free and meminfo are more in line with the roughly-10MB-per-GB-not-visible 'norm', but the mtrr looks the same.
so with 5GB:

Code:

free:
             total       used       free     shared    buffers     cached
Mem:          4958         55       4902          0          0         20
Swap:          509          0        509

hwinfo:
12: None 00.0: 10102 Main Memory
  [Created at memory.61]
  Unique ID: rdCR.CxwsZFjVASF
  Hardware Class: memory
  Model: "Main Memory"
  Memory Range: 0x00000000-0x135eb4fff (rw)
  Memory Size: 5 GB
  Config Status: cfg=new, avail=yes, need=no, active=unknown

meminfo:
MemTotal:      5077716 kB (/1024=4958.70703125)
MemFree:       5020340 kB
Buffers:           548 kB
Cached:          20812 kB
SwapCached:          0 kB
Active:          14276 kB
Inactive:        12132 kB
SwapTotal:      522072 kB
SwapFree:       522072 kB
Dirty:               4 kB
Writeback:           0 kB
AnonPages:        5196 kB
Mapped:           2228 kB
Slab:             9132 kB
SReclaimable:     3664 kB
SUnreclaim:       5468 kB
PageTables:        564 kB
NFS_Unstable:        0 kB
Bounce:              0 kB
CommitLimit:   3060928 kB
Committed_AS:     7668 kB
VmallocTotal: 34359738367 kB
VmallocUsed:      9724 kB
VmallocChunk: 34359728119 kB
HugePages_Total:     0
HugePages_Free:      0
HugePages_Rsvd:      0
HugePages_Surp:      0
Hugepagesize:     2048 kB

mtrr:
reg00: base=0x00000000 (   0MB), size=2048MB: write-back, count=1
reg01: base=0x80000000 (2048MB), size=1024MB: write-back, count=1
reg02: base=0xc0000000 (3072MB), size= 256MB: write-back, count=1

in removing the memory remapping option from the BIOS could Asus have implemented some kind of if/then for that option depending on if you have up to 4GB or >4GB of memory installed?

I guess I should have tried installing the HD3650 while I had 5GB of RAM in there and seen if I could log out without locking up everything, but I'm growing very weary of plugging that card in only to plug in the 8600 again after a couple hours of fruitless hoop jumping. *sigh*

**oblivious_maximus** · 22 April 2008, 04:29 AM

Chalk it up to 64bit oddities I guess.

After my first 3 months with a 64bit CPU (and a 64bit OS), I decided it was time to see if the grass was greener on i386. So far it is. With a 'bigmem' kernel, I'm seeing what I'd expect in free (4053MB, about 10MB/gig not listed (still wondering why that is though)), but the mtrr still seems completely wrong. Only I can't find enough/any straightforward-for-dummies information on whether what I'm seeing in /proc/mtrr is actually completely wrong, or even if I should care at all. Presumably the mechanism for allowing the OS to control how memory is cached (if my understanding is accurate) should know about all the memory in a system, not just most of it, should it not?

If anyone can point me to some decent info on the mtrr in Linux and making sure that it's set up properly, or some info that explains even a little why mine doesn't cover all my ram, I would really appreciate it.

here's all that same info I've been posting, from my current install, maybe it'll be useful...

Code:

free -m -o
             total       used       free     shared    buffers     cached
Mem:          4053       3895        158          0          0       3638
Swap:          509          0        509

meminfo
MemTotal:      4150800 kB
MemFree:        162012 kB
Buffers:            36 kB
Cached:        3725796 kB
SwapCached:          0 kB
Active:         556940 kB
Inactive:      3356936 kB
HighTotal:     3276480 kB
HighFree:        11852 kB
LowTotal:       874320 kB
LowFree:        150160 kB
SwapTotal:      522072 kB
SwapFree:       522072 kB
Dirty:             200 kB
Writeback:           0 kB
AnonPages:      188044 kB
Mapped:          80160 kB
Slab:            47500 kB
SReclaimable:    32636 kB
SUnreclaim:      14864 kB
PageTables:       2880 kB
NFS_Unstable:        0 kB
Bounce:              0 kB
CommitLimit:   2597472 kB
Committed_AS:   470572 kB
VmallocTotal:   118776 kB
VmallocUsed:     52460 kB
VmallocChunk:    56820 kB
HugePages_Total:     0
HugePages_Free:      0
HugePages_Rsvd:      0
HugePages_Surp:      0
Hugepagesize:     2048 kB

mtrr
reg00: base=0x00000000 (   0MB), size=2048MB: write-back, count=1
reg01: base=0x80000000 (2048MB), size=1024MB: write-back, count=1
reg02: base=0xc0000000 (3072MB), size= 256MB: write-back, count=1

hwinfo
12: None 00.0: 10102 Main Memory
  [Created at memory.61]
  Unique ID: rdCR.CxwsZFjVASF
  Hardware Class: memory
  Model: "Main Memory"
  Memory Range: 0x00000000-0xfd583fff (rw)
  Memory Size: 4 GB
  Config Status: cfg=new, avail=yes, need=no, active=unknown

I guess if I plug in the HD3650 and it works without locking up my whole system really hard then I won't be so bothered by the mtrr discrepancy. All the same I'd love to read an explanation somewhere.

**Moustacha** · 27 April 2008, 07:16 AM

hwinfo says 3GB+768MB to me as well.

Code:

free -mo
             total       used       free     shared    buffers     cached
Mem:          3949       3921         28          0       1518       1808
Swap:          956         41        914

cat /proc/meminfo 
MemTotal:      4044512 kB
MemFree:         30732 kB
Buffers:       1553352 kB
Cached:        1850676 kB
SwapCached:       1608 kB
Active:         614196 kB
Inactive:      3257476 kB
SwapTotal:      979956 kB
SwapFree:       936956 kB
Dirty:             348 kB
Writeback:           0 kB
AnonPages:      466112 kB
Mapped:          95916 kB
Slab:            92468 kB
SReclaimable:    63096 kB
SUnreclaim:      29372 kB
PageTables:      17000 kB
NFS_Unstable:        0 kB
Bounce:              0 kB
CommitLimit:   3002212 kB
Committed_AS:  1007304 kB
VmallocTotal: 34359738367 kB
VmallocUsed:     18712 kB
VmallocChunk: 34359719639 kB

 cat /proc/mtrr 
reg00: base=0x00000000 (   0MB), size=2048MB: write-back, count=1
reg01: base=0x80000000 (2048MB), size= 512MB: write-back, count=1
reg02: base=0x100000000 (4096MB), size=1024MB: write-back, count=1
reg03: base=0x140000000 (5120MB), size= 512MB: write-back, count=1

I've only got 4GB Main Memory, 512MB video card memory. I haven't been bothered checking this out before.

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The mystery of my memory's missing megabytes

The mystery of my memory's missing megabytes

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