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

David Newall david.newall at auug.org.au
Wed Mar 29 21:31:35 EST 2006

Gary R. Schmidt wrote:
> There are two areas where kernel allocations are mode, one, over there
> ==> is for allocations of 8Kb and more, the other, over there <== is for
> allocations less than 8Kb.
That part you explained clearly.

> I need 10Kb, but there is no space in the >8 zone.  Bad luck.  There may
> be 63Kb free in the <8 zone, and 32Kb of that is contiguous, but, bad
> luck, you can't get it.
When a machine, with memory measured in hundreds of megabytes, has its 
large buffer pool so full that it can't scrape together a measly 10KB, 
then that machine is in trouble.  These buffers are simply staging areas 
for data on its way from here to there, and if you run out of buffers it 
means something over there stopped.  Satisfying a largish allocation 
from the short buffer pool probably would be the worst thing to do.

> Well, what you have mentioned above seems to me to have a lot to do with
> how you parcel out memory.
No.  Not at all.  It was to do with how you parcel out address space.  
Not the same thing at all.

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