Re: [gentoo-user] 2GB of RAM

[David Klempner <klempner@imsanet.org>]

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* Ralph Slooten <axllent@gmail.com> [2006-06-21 00:15]:
> I upgraded yesterday to 2.6.17 and also noticed that there was no split
> option. Not thinking much of it I installed the kernel which works fine,
> except now /proc/kcore reports 897M, and `free` something to that effect
> too.
> 
> So I take it I'm only using just less than 1/2 my RAM now, correct?

Right.

> With 2GB of RAM, Do I now have to enable the embedded option (which
> gives me a lot more options, most likely all of which I don't need), and
> then select the 2/2 split, or .... ?

Actually, I side with the kernel developers on this; the fact that
they're hiding the VMSPLIT options is basically a subtle hint that they
don't want people using them who don't *really* know what they're doing.

I strongly suggest using CONFIG_HIGHMEM, and sticking with the default
3/1 split. (I mean, it's *slightly* slower, but on the other hand what
caused them to do this was random breaking of java that took a long time
to diagnose.) That said...

> I noticed too that if I select the embedded option, but unselect all new
> options that come with it I still get the memory split options. Is this
> the right way to go?

NO. As in, all of those options (with the exception of
CONFIG_KALLSYMS_EXTRA_PASS) default to yes, and all of those defaults
are very important. If you disable them, you will, for example, break
most of the kernel's logging (printk), lose the ability to get core
dumps, and lose futexes (which will break a lot of modern threading).
Basically, saying no to any option option on that page (with the
exception of the KALLSYMS stuff) *WILL* break your system.

So, make sure that everything, except CONFIG_KALLSYMS_EXTRA_PASS, on
that page is enabled. (that might be what you meant in the first place,
of course, but it's worth making sure...) All you need to be able to
select the VMSPLIT options is CONFIG_EMBEDDED (that is, saying yes to
the "Configure standard kernel features (for small systems)" item) which
doesn't actually have any impact on the code.

Hope this helps.

-- 
David Klempner

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