hugemem kernal and CentOS 5 (32 bit)


I need to setup a server to host a number of dynamic websites powered by Linux, Apache, MySQL and PHP.

I plan to use CentOS 5 (32 bit).

I have 4 GB of total RAM and was told that the hugemem kernal is required to address more than 3GB for single processes.

How stable is the hugemem kernal?  Is it needed?

Should I install the hugemem kernal? and if so where do I get it?

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Pétur Ingi EgilssonSoftware Engineer -- ConsultantCommented:
According to "The x86 "Hugemem" kernel is not provided in CentOS 5."
It seams they are using PAE Kernel for Centos 5.
To install the PAE kernel use the command : `yum install kernel-PAE`
Artysystem administratorCommented:
>  Is it needed?

No. It's for RAM > 4Gb.

Standard kernel should work fine with up to 4Gb RAM.

Standard kernel can address something like 3.9G(4G-128M) of memory, so having 4G ram and standard kernel cause loosing the (small) amount of memory.

So for 4G ram and more - kernel-PAE

Also, it seems that I was wrong with the 4G per process in hugemem kernel. The hugemem kernel was shipped with CentOS 4.X, but it seems, that version 5 dropped the support for that. Probably in favor to 64bit system.
Duncan RoeSoftware DeveloperCommented:
Hugemem is a single config option - if you configure your own kernels. <rant>Missing 128MB is peanuts - on my 64-bit system I lose 512MB from 4GB because of stupid 32-bit BIOS that reserves address space from 3.5 - 4G - it doesn't actually use it, it just hides it.</rant>
> Hugemem is a single config option
Not really. On RH4(centos4) hugemem kernel included 4G/4G kernel/user memory split path. That why I was referring to 4G for single process on hugemem kernel.

> Missing 128MB is peanuts
To have 128M pagecache larger, or 128M smaller, gives You 256M difference already ;)))) <lol>

> stupid 32-bit BIOS that reserves address space from 3.5 - 4G
O that's strange. I have this supermicro mobo with bios option to reserve 0.5G address space, but no matter what I set it to, linux 64bit sees 5966M ot of 6G physical.
It somehow remaps it, cause largest phisical address seen by kernel is 0x1b0000000 =~ 6.75G

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