here's a patch to the arm32 machdep.c to implement the BUFCACHE
stuff i did on the i386 (and others have subsequently done for
other ports).

the last kernel i built with this was a month ago, but my cvs
update cleanly merged these changes. still, it probably pays to
check.

Index: machdep.c
===================================================================
RCS file: /cvsroot/src/sys/arch/arm32/arm32/machdep.c,v
retrieving revision 1.54
diff -c -r1.54 machdep.c
*** machdep.c	1998/10/19 22:09:18	1.54
--- machdep.c	1998/11/04 22:59:54
***************
*** 144,149 ****
--- 144,154 ----
  #else
  int	bufpages = 0;
  #endif
+ #ifdef BUFCACHE
+ int	bufcache = BUFCACHE;	/* % of RAM to use for buffer cache */
+ #else
+ int	bufcache = 0;		/* fallback to old algorithm */
+ #endif
  
  int cold = 1;
  
***************
*** 599,616 ****
  #endif
                                                                           
  	/*
! 	 * Determine how many buffers to allocate.  We use 10% of the
! 	 * first 2MB of memory, and 5% of the rest, with a minimum of 16
! 	 * buffers.  We allocate 1/2 as many swap buffer headers as file
! 	 * i/o buffers.
  	 */
- 
  	if (bufpages == 0)
! 		if (physmem < arm_byte_to_page(2 * 1024 * 1024))
! 			bufpages = physmem / (10 * CLSIZE);
! 		else
! 			bufpages = (arm_byte_to_page(2 * 1024 * 1024)
! 			         + physmem) / (20 * CLSIZE);
  
  #ifdef DIAGNOSTIC
  	if (bufpages == 0)
--- 604,638 ----
  #endif
                                                                           
  	/*
! 	 * If necessary, determine the number of pages to use for the
! 	 * buffer cache.  We allocate 1/2 as many swap buffer headers
! 	 * as file I/O buffers.
  	 */
  	if (bufpages == 0)
! 		if (bufcache == 0) {		/* use old algorithm */
! 			/*
! 			 * Determine how many buffers to allocate. We use 10%
! 			 * of the first 2MB of memory, and 5% of the rest, with
! 			 * a minimum of 16 buffers.
! 			 */
! 			if (physmem < arm_byte_to_page(2 * 1024 * 1024))
! 				bufpages = physmem / (10 * CLSIZE);
! 			else
! 				bufpages = (arm_byte_to_page(2 * 1024 * 1024)
! 					 + physmem) / (20 * CLSIZE);
! 		} else {
! 			/*
! 			 * Set size of buffer cache to physmem/bufcache * 100
! 			 * (i.e., bufcache % of physmem).
! 			 */
! 			if (bufcache < 5 || bufcache > 95) {
! 				printf(
! 		"warning: unable to set bufcache to %d%% of RAM, using 10%%",
! 				    bufcache);
! 				bufcache = 10;
! 			}
! 			bufpages= physmem / (CLSIZE * 100) * bufcache;
! 		}
  
  #ifdef DIAGNOSTIC
  	if (bufpages == 0)