[pups] Progress on 2.11BSD kernel

Johnny Billquist bqt at update.uu.se
Thu Mar 20 09:34:21 AEST 2003

On Wed, 19 Mar 2003, Steven M. Schultz wrote:

> 	The buffer cache must be entirely mapped by UMRs - so if you have a 
> 	32KB buffer the kernel will reserve 4 UMRs on a UNIBUS system.   
> 	Realistically a 64KB buffer cache is about the maximum a UNIBUS system 
> 	can have because that takes 8 of the UMRs.  

Are the UMRs allocated and set up statically?
(I haven't looked inside 2BSD for a while now, and can't remember much of
the internals anymore.)

> 	With the old (thankfully no longer in use, etc) 3Com ethernet boards
> 	you had to disable 4 UMRs so the system could access the memory in the
> 	card - that made for a very tight fit.

How many UMRs does the system use? 8 for buffer cache, you might expect
one or two DH11s, that would require a few more, ethernet takes another
few, but it seems there shouldn't be such a shortage.

What did I miss?


Johnny Billquist                  || "I'm on a bus
                                  ||  on a psychedelic trip
email: bqt at update.uu.se           ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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