To: arch@_ERASE_freebsd.org
cc: jhs@
Subject: src/sys/i386/i386/machdep.c if (MAXMEM/4 < Maxmem) Maxmem = MAXMEM/4;

In src/sys/i386/i386/machdep.c

1.1.5 code was
	#ifdef MAXMEM
	if (MAXMEM/4 < Maxmem)
	Maxmem = MAXMEM/4;
	#endif
2.current code is:
	Maxmem = MAXMEM/4;
1.1.5 seems safer though !

If we asert 
	options "MAXMEM=16384"
& then borrow the kernel to run on an 8M system,
wont this now screw up badly ?

I offer this patch:
--------
*** old/src/sys/i386/i386/machdep.c     Tue Nov 15 19:09:00 1994
--- new/src/sys/i386/i386/machdep.c     Mon Nov 21 02:38:03 1994
***************
*** 287,292 ****
--- 287,296 ----
  #ifdef BOUNCE_BUFFERS
  	/*
  	 * If there is more than 16MB of memory, allocate some bounce buffers
+ 	 * (because ISA bus with just 24 address bits prevents addresses
+ 	 * above 16M being used to access either ISA cards such as disc
+ 	 * controllers, (or even EISA disc controllers running in ISA
+ 	 * compatibility mode)).
  	 */
  	if (Maxmem > 4096) {
  		if (bouncepages == 0)
***************
*** 1307,1313 ****
  	Maxmem = pagesinext + 0x100000/PAGE_SIZE;
  
  #ifdef MAXMEM
! 	Maxmem = MAXMEM/4;
  #endif
  	/*
  	 * Calculate number of physical pages, but account for Maxmem
--- 1311,1338 ----
  	Maxmem = pagesinext + 0x100000/PAGE_SIZE;
  
  #ifdef MAXMEM
! 	/* In /sys/i386/conf/GENERIC, using
! 	 *   	options "MAXMEM=16384"
! 	 * gets kernel here to use just first 16M,
! 	 * (useful for such as when testing ISA systems where one 
! 	 * suspects the 16 to 32M area of RAM is not cached 
! 	 * (eg Gigagbyte ISA-486 Taiwan motherboard owned by
! 	 * jhs@
! 	 */
! #define K_PER_PAGE    ( PAGE_SIZE / 1024 )
! 	if ( Maxmem > ( MAXMEM / K_PER_PAGE ) )
! 		{
! 		printf("%s %d to %d pages of %d bytes,\n(%ld %s %ld).\n",
! 			"Reducing memory from",
! 			Maxmem,
! 			MAXMEM / K_PER_PAGE,
! 			PAGE_SIZE,
! 			(long)Maxmem * (PAGE_SIZE),
! 			"reducing to",
! 			((long)(MAXMEM/K_PER_PAGE )) * (PAGE_SIZE)
! 			);
! 		Maxmem = MAXMEM / K_PER_PAGE;
! 		}
  #endif
  	/*
  	 * Calculate number of physical pages, but account for Maxmem
--------

PS It seems there's rather too many manifest constants such 4096, 4, 1024,
floating around in machdep.c, hence K_PER_PAGE.

Julian Stacey <jhs@