Re: Kernel optimizations for small machines
Enrico Zini writes...
> However, he's had ideas on how make things more efficient for computers
> which need more memory than what they have (for example, a Gnome or KDE
> desktop on a <256Mb ram). One of his ideas was, in case of allocating
> with all the physical memory full, instead of copying pages to swap
> (which has a 2/3Mb/s bandwidth), to compress them and keep them in RAM
> (which has a bandwidth that is order of magnitude faster, and has very
> good compression ratios for the data usually found in-memory.
>
> This would be supercool! However, he said, there is little or no
> commercial interest on anything like this, so he warned that we should
> not expect to see this coming anytime soon unless we code it ourselves.
IIRC Connectix's "RAM Doubler" product for MacOS has been doing this for
years. If the CPU overhead of compression/decompression/etc is lower than the
overhead paging to/from disk then I guess it might be a good idea. But being
in either situation is pretty painful.
"Memory is like an orgasm. It's a lot better if you don't have to fake it."
-- Seymour Cray
I think freegeek has gotten to the point where the system spec for the
recycled machines they're building is a minimum of 80mb. For people trying to
maintain collections of systems with less than that I bet they could send you
a ton of 8 and 16mb dimms :) (or maybe just some better systems)
There is another class of systems that are affected though, and that's systems
who's memory can't be upgraded at all. There are some systems that are
potentially interesting to non-profits due to price/power/heat/size
considerations that fall into this category. Some examples
* i-opener and other net appliances
* Sega Dreamcast, Sony PS2 and other video game consoles
* PDAs/palmtops/handtops
One trick that's been used with some of these is that sometimes there is
memory available in the peripherals of the system than can be used as a block
device and mounted as a fast swap partition. For example the Dreamcast system
has 8mb of video ram, if you only use 1mb for video you can use the other 7mb
as fast swap (the audio device has a small amount of ram too, but maybe not
worth the effort).
One way to look at the low RAM problem is: Is your time better spent working
on RAM doubling or tuning/replacing the bloated applications wasting RAM? Once
people have done a good enough job on the latter, maybe the former will be
interesting to pursue. (and maybe they have already, thing like jailbait linux
etc. do a lot with a little RAM)
--
Matt Taggart
taggart@debian.org
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