[AUUG-Talk]: Re: [BUGA] Sell me an Apple!

David Newall davidn at rebel.net.au
Mon Mar 27 23:38:54 EST 2006

Gary R. Schmidt said:
> Oh, it's _way_ beyond crap.  I just started working with it, my first
> "Oh No!" is this - there is a Kernel Memory Allocation Zone where kernel
> allocations greater than 8Kb go.
> Its size is calculated based on physical RAM, and it is *fixed*.

This sounds like some sort of buffer cache, and an assignation based on
size of physical RAM sounds fair.  You can't really be paging these
things; in fact they are probably used for paging, amongst many other
purposes.  You don't want to fill RAM with it, if for no other reason than
that yoy need some of that RAM for processes which, presumably, are
creators and consumers of these kernel buffers.  Picking a fraction of RAM
as an upper bound is one way of balancing competing needs, and who's to
say it's wrong?  Not you, I'll wager.

> When I was told about this, my reaction was an incredulous, "Apple's
> programmers haven't learned /anything/ since 1986?!?!?!?!?"

I don't know to what you allude, but I was "there" in 1986, so I'm going
to make some guesses.  Stop me if I go wrong.  1984 was when Apple showed
us "why 1984 [wasn't] like 1984."  They gave us Macintosh.  It was a new
platform in many ways, including what appeared at the time to be a
ludicrously large address range, and Apple, in keeping with the habits
they had adopted from day one, split that space according to various
purposes; so much address space for ROM, so much for hardware I/O; so much
for a frame buffer; and so on.  I'm guessing that the lessons they were
supposed to have learned in 1986 all relate to that.  That doesn't seem to
have much in common with "Kernel Memory Allocation Zones."

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