You're welcome. One way or another I stumbled across sapphirecat's article, and I was lucky enough to bookmark it. Great info, no doubt

BTW. There is another good reason for enabling high-memory support, or specifically PAE (< 64GB). Having PAE enabled makes it possible to use the NX bit on AMD64 and newer Intel processors. With this bit the kernel can make writable pages non-executable (and executable pages read-only), which helps protecting against buffer overflow exploits. If you have PAE enabled on a CPU that has the NX bit, you should see something like the following line in the kernel output:

That is a good link and not too many people know about the memory cap at less than a Gig. I just upgraded my Powerbook Pismo to 1 Gb of ram and /proc/meminfo was only reporting that I had just under 800 Mb of memory. So would 'free'... I recompiled for High Mem Support and now the kernel see's all 1008 Mb of ram.

It's very misleading implying that you only need to enable High Mem Support if you have over a Gig. More like over 800Mb.... I agree, this should be default. I was aware there would be a little overhead in doing so but it IS negligible. Not even enough to bother mentioning. I'd rather have my extra RAM...

By upgrading to kernel 2.6.16, you can have up to 1G (all of it) under LOWMEM. Previosly, this required a patch (e.g. Con Kolivas). Now there is no need for HIGHMEM just to utilize 1G.

Pat's kernels still assume a 486 as the smallest common denominator.
The fact that many geeks have high-end machines with tons of RAM or
64-Bit CPUs doesn't really warrant as 4GB RAM default for the kernel.


Cheers,
Tink

Hmmm. I am using 2.6.16.11 and only 800MB of it was recognized. Perhaps there was a specific option I over looked that I didn't enable. Altho, I think your implying that nothing needs to be done. Just use a 2.6.16 kernel? Didn't do the trick here. Was missing out on 200mb til I ticked High Mem.

A gig of RAM isn't alot these days. Alot of computers come with a gig or more from the factory. I wonder what the percentage of machines running Slackware are 'i486' with low mem as compared to more modern machines with a gig or more. Those would be some interesting statistics. I have a feeling the old machine running Slack is few and far inbetween compared to newer rigs running Slackware. Manufactures like Dell are selling computers dirt cheap nowadays. Most people I know with old boxes throw them away and get a new one for very little cost.

Still, it takes minimal effort to recompile a kernel. Generally speaking, the average Slackware user doesn't mind doing things him/her self... So I suppose the whole point is moot.

/me coughs ...
Even if that is the case, the 486, low-mem kernel will most likely
work on a new rig, and allow you to recompile a kernel that suits
your needs (and on my wives AMD64 a 2.6.16.9 recompile takes well
under 10 minutes). The other way around IT WON'T WORK.

And now stop being selfish. :P


Cheers,
Tink

Sorry, I should have been more clear. There is another option. First, select LOWMEM. Then, choose the correct memory split.

1G, LOWMEM.

Sorry about the confusion.

Thanks for clarifying. I guess most of the confusion is that I'm usually on PPC... There is only one option available and that's
[*] High memory support

period... Good to know tho for x86.

I was just thinking it would be convienent on some people if it was default. Actually, I could care less because I build everything myself.

thanks for this info - i had been wondering the same thing.. i have 1024 MB in this machine (2.x512) and it notes that i can only use around 850+or there abouts.
I had also chosen the 1GB< option as it said seemed from reading something else that i might suffer a performance hit if i choose the other option (unless i actually have 3GB or RAM or something)..
Being that i have way more ram (even at 880) than my system ever consumes i think i will keep the <1GB option on but it is nice to know the 'nitty gritty' =)

Shilo, are you able to elaborate as to why you pick the 3GB split.. ?
I also have 1GB ram but am on 2.6.15 - it reports 880MB too. i might go download .16 now and see how i go.. more fun and games =)

Just remember that one nice thing about linux is that is *does* actually *use* the memory you have installed, in some way or another (ever notice your "top" memory usage?).

I can understand that you may not be rendering videos or doing other memory-consumptive tasks, but, at least in my case, I opted (when I was using 32-bit kernel) for the highmem option because I *paid* for 1GB of RAM and didn't want to suffer a 12% loss in memory just because of kernel configuration.

Your mileage may vary and I understand if you don't want to enable it for performance reasons or otherwise.

The 3G_OPT split is the only LOWMEM option that utilizes the full 1G of RAM. Download the latest kernel and look at the help when compiling (using "make xconfig" or the "?" under "make menuconfig". It's a new option in 2.6.16.

It would be absurd to make it the default.

I have never, in my entire life, used a PC with over 512 MB of ram. There are many more like me. Besides, the PCs that DO have more than 800MB of ram are generally the ones that can compile a new kernel in less than 30 minutes. It makes more sense for the people with the newer machines to compile a kernel than for a person with an older machine to have to compile a kernel. The loss in performance IS noticeable on a machine with less than 800MB of ram, and those are the machines that would spend hours compiling a kernel to correct it.

187807. yes i agree - it sux to lose 12% of something you paid for ...
I just downloaded the .16 kernel and have since re-compiled and all is looking great. =)
Im sure i will not notice any different but it is still cool getting the most out of what i have got...(or at least thinking i am as i can see it written on the screen). To date i dont think my page file has been used once..
* this is also the first machine i have had with more than 256mb ram - i really wanted a 'pimp' rig this time =)