Arch Linux

frigg

Member

From: Germany, Europe

Registered: 2006-10-30

Posts: 46

Config_highmem64g

Hi there,

I don't know if this issue was discussed some time ago.

The new Hardware suppoprts RAM with 4 or more GB. I would gess the limitation to CONFIG_HIGHMEM4G=y in the kernel config file has to be dropped to support more than 4 GB on 32 bit kernels. Well I know that a process on a 32 bit kernel can't go beyond 2 GB but this limitation is valid only for one process and not for the whole system.

It would be very nice if there is a kind of a *-bigmem kernel for download in the repository. Is there anybody working in this direction?

regards,

Frank

lilsirecho

Veteran

Registered: 2003-10-24

Posts: 5,000

Re: Config_highmem64g

I surmise that 64bit systems have arrangements for greater than 4G, but X86 32bit systems cannot address greater than 4G and never will.

---

Prediction...This year will be a very odd year!
Hard work does not kill people but why risk it: Charlie Mccarthy
A man is not complete until he is married..then..he is finished.
When ALL is lost, what can be found? Even bytes get lonely for a little bit!     X-ray confirms Iam spineless!

kishd

Member

Registered: 2006-06-14

Posts: 401

Re: Config_highmem64g

Interestingly some motherboards eg ASUS P5B VM cannot address memory greater than 3G without PAE (physical address extension) so the kernel has to be recompiled with highmem = 64g to enable pae.

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---for there is nothing either good or bad, but only thinking makes it so....
Hamlet, W Shakespeare

frigg

Member

From: Germany, Europe

Registered: 2006-10-30

Posts: 46

Re: Config_highmem64g

Hi kishd,

Interestingly some motherboards eg ASUS P5B VM cannot address memory greater than 3G without PAE (physical address extension) so the kernel has to be recompiled with highmem = 64g to enable pae.

Yes that is a well known issue (e.g Acer Aspire 5633 laptop with 4 GB RAM). Without PAE there is a limitation about 3,5 GB depending on system/hardware configuration. The complete 4 GB can't be used without setting the highmen to 64g.

For this reason I repeat my request to a bigmem kernel for 32-bit systems in the arch repo.

best regards,

Frank

frigg

Member

From: Germany, Europe

Registered: 2006-10-30

Posts: 46

Re: Config_highmem64g

Hi,

I surmise that 64bit systems have arrangements for greater than 4G, but X86 32bit systems cannot address greater than 4G and never will.

And what do you think about this 32 bit system:

uname -a
Linux <hostname> 2.6.9-55.ELsmp #1 SMP Fri Apr 20 17:03:35 EDT 2007 i686 i686 i386 GNU/Linux

cat /etc/issue
Red Hat Enterprise Linux ES release 4 (Nahant Update 5)
Kernel \r on an \m

cat /proc/meminfo
MemTotal:      8309184 kB
MemFree:       5481440 kB
Buffers:        147176 kB
Cached:        1874844 kB
SwapCached:          0 kB
Active:        1674696 kB
Inactive:      1075504 kB
HighTotal:     7469404 kB
HighFree:      4856512 kB
LowTotal:       839780 kB
LowFree:        624928 kB
SwapTotal:     4096564 kB
SwapFree:      4096564 kB
Dirty:            6720 kB
Writeback:           0 kB
Mapped:         764956 kB
Slab:            54580 kB
CommitLimit:   8251156 kB
Committed_AS:  2230808 kB
PageTables:       4556 kB
VmallocTotal:   106488 kB
VmallocUsed:      4972 kB
VmallocChunk:   101364 kB
HugePages_Total:     0
HugePages_Free:      0
Hugepagesize:     2048 kB

And believe me there is nearly the whole memory in use (not in this snapshot shown)

regards,

Frank

broch

Banned

From: L.A. California

Registered: 2006-11-13

Posts: 975

Re: Config_highmem64g

simply re-build kernel. Most desktop systems don't have more than 2GB RAM, No point of introducing overhead. Compiling new kernel will take 20 min or less on modern system.

Last edited by broch (2007-11-08 15:44:09)

lilsirecho

Veteran

Registered: 2003-10-24

Posts: 5,000

Re: Config_highmem64g

frigg;

The statement I made re: x86 is still valid since the cpu is changed for the PAE models which do have 64G capability for 32bit systems, but as such, are special devices not strictly x86.

I have in the past years modified the kernel as others suggested to permit 4G highmem when the kernel did not provide it as installed.

I assume that only one of the options can be enabled, namely 4G or 64G. 

The kernel aside, even 16GB of ram installed is a wallet-burner for sure!! 

Best of luck with your kernel modification and hopefully you have the RAM to make good use of the change.

I wait on the sidelines!!

---

Prediction...This year will be a very odd year!
Hard work does not kill people but why risk it: Charlie Mccarthy
A man is not complete until he is married..then..he is finished.
When ALL is lost, what can be found? Even bytes get lonely for a little bit!     X-ray confirms Iam spineless!

tpowa

Developer

From: Lauingen , Germany

Registered: 2004-04-05

Posts: 2,322

Re: Config_highmem64g

having highmem activated caused much trouble on older hardware some time ago, that's the reason for not adding it.

frigg

Member

From: Germany, Europe

Registered: 2006-10-30

Posts: 46

Re: Config_highmem64g

Hi lilsirecho,

I assume that only one of the options can be enabled, namely 4G or 64G.

Ok there were some missunderstanding. Of course you can use either 4G or 64G as highmem parameter but not both, which doesn't make any sense. Btw PAE is supported on x86 since Intel Pentium Pro and  AMD Athlon.

frigg

Member

From: Germany, Europe

Registered: 2006-10-30

Posts: 46

Re: Config_highmem64g

Hallo Tobias,

having highmem activated caused much trouble on older hardware some time ago, that's the reason for not adding it.

Well I doesn't want a general 64 G capable kernel. I asked if it's possible to provide something like an official "kernel26bigmem" package in the repository. Every user has to made a decision if the standard kernel is used which is the default or for systems with RAM from 4 Gb and upwards there is a PAE enabled kernel for installing available.

dmartins

Member

Registered: 2006-09-23

Posts: 360

Re: Config_highmem64g

Somehow I don't think there are enough people who would make use of this feature to warrant a dev looking after another kernel in the official repository. Arch has the AUR for this kind of thing, where anyone can submit and maintain packages.