Re: dynamically changing available memory

Peter Swain (
Sun, 17 May 1998 17:52:52 +1000 (EST)

> David Ford wrote:
> > it would please me to no end to be able to pull out a failing/failed
> > memory module and replace it and the kernel continue on it's merry little
> > way.
> sure and the simm-dimmdaemon with the knowledge of yer chipset,
> will tell ye which rammodule of Bank(0..x) to replace,
> 'cause of sig11 and similar HW/Mem_Errors.
> Har, har

well, one day, yes...
it doesn't take much, really

as a solution to the how-can-i-use-discontiguous-memory thread, too,
one day we should have in-memory images implicitly resident on the 'swapfile'
/dev/mem (with a swap_priority of 0, as distinct from the current -1, -2, ...)
then we could implement the above proposal with swapoff-like semantics,
removing an address range.

what happens to the procs/kernel_structures/etc living there?
same as what happens when a swap-space develops errors!
if you'rre paranoid enuff, you use mem as a RAID device.
not easy, to implement, but that's the generalisation you base it on.

but the easy part which comes with this generalisation is that one can
*add* memory --- the gap-at-16Mb and mem-bigger-than-64Mb problems
go away when you can just boot a vanilla kernel using at most 15Mb,
and then do a "swapon -priority=0 -lo=15Mb -hi=192Mb /dev/mem"
from the usual /etc/rc*.

anything with swap-prio >= 0 is real mem!

i can imagine handling that scarce resource of L2 cache as prio==1
and L1 cache as prio==2, and the goodness() function deriving its
current-proc-is-favoured policy from posession of a prio==3 resource
representing running-on-this-processor.
the using-fpu property is similar.

play with it.
i suspect linus et al already have this in mind,
that's what the -ve swap priorities immediately suggested to me....

Peter Swain ^..^ +61 2 9698 2322 (office) (00) +61 419 431 088 (mobile)
Evolutionary software, revolutionary results +61 2 9519 0171 (home)

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