Pre-allocating memory?

your_shadow03 · 02-04-2009, 10:46 PM

I have RHEL AS 4 Update 6 x86_64 Machine with 16 GB RAM running on one of the Blade Server.I want to pre-allocate 8GB Memory for performance testing.How Can I make it happen?

NOTE - physical removal of memory is no option).

Didier Spaier · 02-05-2009, 01:48 AM

Yes.

Quoted from /usr/src/linux-2.6.27-7/Documentation/kernel-parameters.txt:

Code:

	mem=nn[KMG]	[KNL,BOOT] Force usage of a specific amount of memory
			Amount of memory to be used when the kernel is not able
			to see the whole system memory or for test.
			[X86-32] Use together with memmap= to avoid physical
			address space collisions. Without memmap= PCI devices
			could be placed at addresses belonging to unused RAM.

	mem=nopentium	[BUGS=X86-32] Disable usage of 4MB pages for kernel
			memory.

	memmap=exactmap	[KNL,X86-32,X86_64] Enable setting of an exact
			E820 memory map, as specified by the user.
			Such memmap=exactmap lines can be constructed based on
			BIOS output or other requirements. See the memmap=nn@ss
			option description.

	memmap=nn[KMG]@ss[KMG]
			[KNL] Force usage of a specific region of memory
			Region of memory to be used, from ss to ss+nn.

	memmap=nn[KMG]#ss[KMG]
			[KNL,ACPI] Mark specific memory as ACPI data.
			Region of memory to be used, from ss to ss+nn.

	memmap=nn[KMG]$ss[KMG]
			[KNL,ACPI] Mark specific memory as reserved.
			Region of memory to be used, from ss to ss+nn.
			Example: Exclude memory from 0x18690000-0x1869ffff
			         memmap=64K$0x18690000
			         or
			         memmap=0x10000$0x18690000

your_shadow03 · 02-05-2009, 02:10 AM

Thats Really Informative Stuff..
I need some more help.How Can I set these kernel parameters anyway?

your_shadow03 · 02-05-2009, 02:33 AM

Do I need to customize the kernel?
On which file I need to make the entry?

Didier Spaier · 02-05-2009, 02:58 AM

These are parameters you can give at time of booting.

To try one, write at time of booting:
<kernel_image_name> <kernel_parameter>=<value>

e.g. My only kernel image name for now is Linux (set up in lilo). So I could type at start up:
Linux mem=123456

Once you have found the good value(s) for your parameter(s) you can include it in an "append=" statement if yu use lilo. For grub I do not know, I do not use it.

your_shadow03 · 02-05-2009, 03:06 AM

I am using GRUB and that too a Blade server. Do I need to reboot for GRUB to display or anything I can in runtime?
I will need to reboot the blade server?

Didier Spaier · 02-05-2009, 04:19 AM

Of course you have to reboot to set-up kernel parameters values at start up.

If you do not want to and you use the bash shell, you can instead setup limits at run-time, including for memory allocation, to processes launched by the shell.

To know the actual limits open a terminal or a console and type:

Code:

ulimit -a

So to set-up max memory size (value in kbytes):

Code:

ulimit -m <value>

msright1981 · 02-10-2009, 11:35 AM

Hi,

May I ask why do u want to disable the extra memory in your blade without removing them, although you have to restart the server any way? just from curiosity.

your_shadow03 · 02-10-2009, 10:10 PM

All I needed was to restrict the memory for particular process..Thats it...And I should allocate the rest for other process.
But I see no option to allocate remaining to other prcesses?
Do you have any?