putting fedora on a (memory) diet... some suggestions for the kernel config

[Arjan van de Ven]

On Wed, 2006-12-13 at 11:07 -0500, Don Dutile wrote:
> Arjan van de Ven wrote:
> > Looking at kernel memory use (based on 2.6.19 with a fedora config),
> > there's some not that hard ways to gain quite a bit of memory back.
> > 
> > Most important is CONFIG_NR_CPUS, right now that is set to 255 for
> > everyone; this value is used for scaling a LOT of things in the kernel,
> > and the sad thing is it's not even possible today to get a 255
> > core/processor machine (you run out of apic ids well before you get that
> > far).
> > 
> > Setting CONFIG_NR_CPUS to 64 (which is still huge, even 16 would be more
> > than 99.99999% of the people who use fedora will ever use) will save
> > 
> The proper solution: kmalloc-based, per-cpu structs; wire to gs(or is it cs) reg
> like pda is, if performance is an issue.  then you only get what you need.

except if you still do it for each cpu.
And not all of these are per cpu things at all; they just SCALE with the
number of cpus. That's not the same.
ANd the IRQ stuff needs to be there long before kmalloc works.. it's not
that easy.


> Pls! Size it based on memory: on small mem footprints (256MB), make it 32K;
> large memory footprints (1G and above) make it 512KB! (a la "I like to make
> it big for debugging" Jeremy).

logbuf needs to work REAL early, before dynamic allocators work.
> better yet: put tools in place that warn when a function uses X-amt of stack,
>             and analyze those functions/modules for lower stack utilization.

like make checkstack ? been there done that 3 years ago ;)