why pae kernel has only 3G memory

lou

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Oct 15, 2021, 4:30:05 AM10/15/21

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i have stretch, it use 3G memory, 1G memory can't be used

top: KiB Mem : 3038696 total, 2221904 free, 400628 used, 416164
buff/cache
uname: Linux debian 4.9.0-13-686-pae #1 SMP Debian 4.9.228-1
(2020-07-05) i686 GNU/Linux

i think pae kernel can use 4G memory

do i have to upgrade to buster or bullseye?

Andy Smith

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Oct 15, 2021, 5:00:04 AM10/15/21

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Hello,

On Fri, Oct 15, 2021 at 04:27:10AM -0400, lou wrote:
> i have stretch, it use 3G memory, 1G memory can't be used

[…]

> i think pae kernel can use 4G memory

It can be a restriction of your motherboard. Has it ever seen more
than 3G in any operating system?

If your CPU capable of running 64-bit then you could just install an
amd64 kernel. What does

cat /proc/cpuinfo

say?

> do i have to upgrade to buster or bullseye?

This is unlikely to fix things unless it's a known bug.

Cheers,
Andy

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lou

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Oct 15, 2021, 5:30:04 AM10/15/21

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On 10/15/21 4:57 AM, Andy Smith wrote:

Hello,

This is unlikely to fix things unless it's a known bug.

Cheers,
Andy

Thanks!

you are right, i've just tried bullseye, result is same

in memtest86+, 2x2G memory are detected though 3G are tested

my PC is 32bit, it can use only kernel for i386

 cat /proc/cpuinfo:
processor	: 0
vendor_id	: GenuineIntel
cpu family	: 6
model		: 28
model name	: Intel(R) Atom(TM) CPU N280   @ 1.66GHz
stepping	: 2
microcode	: 0x218
cpu MHz		: 1000.000
cache size	: 512 KB
physical id	: 0
siblings	: 2
core id		: 0
cpu cores	: 1
apicid		: 0
initial apicid	: 0
fdiv_bug	: no
f00f_bug	: no
coma_bug	: no
fpu		: yes
fpu_exception	: yes
cpuid level	: 10
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx constant_tsc arch_perfmon pebs bts aperfmperf pni dtes64 monitor ds_cpl est tm2 ssse3 xtpr pdcm movbe lahf_lm dtherm
bugs		:
bogomips	: 3324.98
clflush size	: 64
cache_alignment	: 64
address sizes	: 32 bits physical, 32 bits virtual
power management:

processor	: 1
vendor_id	: GenuineIntel
cpu family	: 6
model		: 28
model name	: Intel(R) Atom(TM) CPU N280   @ 1.66GHz
stepping	: 2
microcode	: 0x218
cpu MHz		: 1000.000
cache size	: 512 KB
physical id	: 0
siblings	: 2
core id		: 0
cpu cores	: 1
apicid		: 1
initial apicid	: 1
fdiv_bug	: no
f00f_bug	: no
coma_bug	: no
fpu		: yes
fpu_exception	: yes
cpuid level	: 10
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx constant_tsc arch_perfmon pebs bts aperfmperf pni dtes64 monitor ds_cpl est tm2 ssse3 xtpr pdcm movbe lahf_lm dtherm
bugs		:
bogomips	: 3324.98
clflush size	: 64
cache_alignment	: 64
address sizes	: 32 bits physical, 32 bits virtual
power management:

Teemu Likonen

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Oct 15, 2021, 5:50:05 AM10/15/21

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* 2021-10-15 08:57:02+0000, Andy Smith wrote:

> If your CPU capable of running 64-bit then you could just install an
> amd64 kernel. What does
>
> cat /proc/cpuinfo
>
> say?

I suggest using command "lscpu". It gives clearer answer:

$ lscpu |head -n2
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit

--
/// Teemu Likonen - .-.. https://www.iki.fi/tlikonen/
// OpenPGP: 4E1055DC84E9DFF613D78557719D69D324539450

signature.asc

piorunz

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Oct 15, 2021, 6:00:05 AM10/15/21

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On 15/10/2021 10:21, lou wrote:

> you are right, i've just tried bullseye, result is same
>
> in memtest86+, 2x2G memory are detected though 3G are tested
>
> my PC is 32bit, it can use only kernel for i386

> address sizes : 32 bits physical, 32 bits virtual
> power management:

Correct me if I am wrong, but how I understand it is this:

Your computer can address 32 bits of memory,
2^32 bits = 4096MB, that's all you can install. PAE will not help.
Doesn't matter if CPU can run 64bit, your memory support is only up to
32bit. Some old computers have 36 or more bits for memory, that allows
them to utilize PAE in 32bit system.

Also, some of your memory is reserved by BIOS for internal use, and as
GPU extra memory. That's why any OS installed or run on this machine
only sees 2.9GB out of 4GB. 1129MB allocated and taken by BIOS.

On my modern PC I write from, I have 64bit CPU, 64bit system and 48bit
memory address space. I have 64GB installed (65536MB).
Only 64292MB visible in Debian. 1244MB taken by UEFI, which is very
similar to your result.

--
With kindest regards, Piotr.

⢀⣴⠾⠻⢶⣦⠀
⣾⠁⢠⠒⠀⣿⡁ Debian - The universal operating system
⢿⡄⠘⠷⠚⠋⠀ https://www.debian.org
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lou

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Oct 15, 2021, 7:50:04 AM10/15/21

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Thank Likonen and piorunz!

https://support.hp.com/us-en/product/hp-t5740e-thin-client/4282707/manuals

from hp's QuickSpecs: Note: Minimum of 1GB and a maximum of 4GB* (2 X 2GB) can be supported (*Up to 1 GB may not be available with 32-bit operating systems due to system resource requirements.)

bios reports 4032M memory, missing 64M might be used by graphics card

it seems to me that hp says that problem of missing memory is with 32-bit OS, not with hp

David Wright

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Oct 15, 2021, 11:10:04 AM10/15/21

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On Fri 15 Oct 2021 at 07:48:06 (-0400), lou wrote:

> https://support.hp.com/us-en/product/hp-t5740e-thin-client/4282707/manuals
>
> from hp's QuickSpecs: Note: Minimum of 1GB and a maximum of 4GB* (2 X
> 2GB) can be supported (*Up to 1 GB may not be available with 32-bit
> operating systems due to system resource requirements.)
>
> bios reports 4032M memory, missing 64M might be used by graphics card

It's not mi-ght but mi-nimum in my download.

> it seems to me that hp says that problem of missing memory is with
> 32-bit OS, not with hp

This problem is well known, and of fading interest to most. Start at:

https://en.wikipedia.org/wiki/3_GB_barrier

If your OP arises out of curiosity, I think that should deal with it.
If you're inconvenienced over it, then it's probably time to retire
or repurpose the hardware. In any case, it looks overdue for a
software upgrade to at least buster, unless something specific is
holding you back.

Cheers,
David.

Andrew M.A. Cater

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Oct 16, 2021, 9:10:05 AM10/16/21

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Upgrade to Buster (following the release notes and hints given in this group)
then to Bullseye. Any particular reason why you must use pae rather than
the standard 32 bit kernel?

Checking, it looks as if the N280 is 32 bit only.

It's a nice, small thin client drawing low power but don't expect
superb performance at this class of hardware.

All the very best, as ever,

Andy Cater

Stefan Monnier

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Oct 16, 2021, 10:40:04 AM10/16/21

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> Any particular reason why you must use pae rather than
> the standard 32 bit kernel?

Hmm... isn't "the standard 32 bit kernel" `linux-image-686-pae` ?

At least the `linux-image-686` package seems to describe itself as for use
only on those machines where `linux-image-686-pae` doesn't work.

Stefan

lou

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Oct 16, 2021, 7:00:05 PM10/16/21

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Thanks, i've just installed linux-image-686, result is same

deloptes

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Oct 17, 2021, 5:00:05 AM10/17/21

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lou wrote:

> Thanks, i've just installed linux-image-686, result is same

you understand that in most cases if you use a 32bit OS with 4GB of memory
you may not utilize 1GB, because the overhead of utilizing this memory
consumes much of this memory with the registers to overcome the 3GB
barrier.
So IMO you have two options:
1. leave it as it is
2. sell 1GB on ebay

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