[Xen-devel] Yet another "Why can't I see all my RAM" question

["Christopher S. Aker" <caker@xxxxxxxxxxxx>]

I know this has been asked a million times, and the typical answer is: 
that specific area of unallocable memory is used for ACPI data and 
framebuffers.  However, I've got two identical machines, one running 
Xen-PAE, one running vanilla 2.6.16:
Vanilla:
MemTotal:     16623588 kB

Xen(PAE)
total_memory: 14336 (MB)

I was a little disappointed to discover that my investment in RAM is 
going to be underutilized in Xen.  I would think if vanilla Linux can 
utilize all the available RAM that Xen would be able to, also.
(XEN) WARNING: Only the first 16 GB of the physical memory map can be 
accessed
(XEN)          by Xen in 32-bit mode. Truncating the memory map...
(XEN) Physical RAM map:
(XEN)  0000000000000000 - 000000000009fc00 (usable)
(XEN)  000000000009fc00 - 00000000000a0000 (reserved)
(XEN)  00000000000e8000 - 0000000000100000 (reserved)
(XEN)  0000000000100000 - 000000007fff0000 (usable)
(XEN)  000000007fff0000 - 000000007ffff000 (ACPI data)
(XEN)  000000007ffff000 - 0000000080000000 (ACPI NVS)
(XEN)  00000000ff780000 - 0000000100000000 (reserved)
(XEN)  0000000100000000 - 0000000400000000 (usable)
(XEN) System RAM: 14335MB (14679612kB)
(XEN) Xen heap: 9MB (10044kB)
(XEN) Using scheduler: Simple EDF Scheduler (sedf)
(XEN) PAE enabled, limit: 16 GB
(XEN) found SMP MP-table at 000ff780
(XEN) DMI 2.3 present.
(XEN) Using APIC driver default
(XEN) ACPI: RSDP (v002 ACPIAM                                ) @ 0x000f9760
(XEN) ACPI: XSDT (v001 A M I  OEMXSDT  0x08000508 MSFT 0x00000097) @ 
0x7fff0100
(XEN) ACPI: FADT (v003 A M I  OEMFACP  0x08000508 MSFT 0x00000097) @ 
0x7fff0281
(XEN) ACPI: MADT (v001 A M I  OEMAPIC  0x08000508 MSFT 0x00000097) @ 
0x7fff0380
(XEN) ACPI: SPCR (v001 A M I  OEMSPCR  0x08000508 MSFT 0x00000097) @ 
0x7fff0410
(XEN) ACPI: OEMB (v001 A M I  OEMBIOS  0x08000508 MSFT 0x00000097) @ 
0x7ffff040
(XEN) ACPI: SRAT (v001 A M I  OEMSRAT  0x08000508 MSFT 0x00000097) @ 
0x7fff3550
(XEN) ACPI: DSDT (v001  H8DAR H8DAR010 0x00000000 INTL 0x02002026) @ 
0x00000000
...
(XEN) PHYSICAL MEMORY ARRANGEMENT:
(XEN)  Dom0 alloc.:   0000000007800000->0000000008000000 (63488 pages to 
be allocated)
(XEN) VIRTUAL MEMORY ARRANGEMENT:
(XEN)  Loaded kernel: c0100000->c06152e4
(XEN)  Init. ramdisk: c0616000->c0616000
(XEN)  Phys-Mach map: c0616000->c0656000
(XEN)  Start info:    c0656000->c0657000
(XEN)  Page tables:   c0657000->c0660000
(XEN)  Boot stack:    c0660000->c0661000
(XEN)  TOTAL:         c0000000->c0800000
(XEN)  ENTRY ADDRESS: c0100000

So what's the scoop here?  Has anyone actually been able to use the full 
16GB in PAE mode?  Is there something I can tweak to get that final 1GB 
back?
Thanks,
-Chris


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