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Path: utzoo!linus!decvax!ittvax!dcdwest!sdcsvax!sdcrdcf!trwrba!pwb
From: pwb@trwrba.UUCP
Newsgroups: net.bugs.4bsd
Subject: Fix for 8 Mb memory limit
Message-ID: <798@trwrba.UUCP>
Date: Wed, 27-Jun-84 16:00:24 EDT
Article-I.D.: trwrba.798
Posted: Wed Jun 27 16:00:24 1984
Date-Received: Sat, 30-Jun-84 06:05:33 EDT
Organization: TRW EDS, Redondo Beach, CA
Lines: 96


1984-0074             TRW/UNIX Modification             1984-0074

NAME
     memory - only 8 megabytes of physical memory supported

DATE ENACTED
     June 22, 1984

KEYWORDS
     kernel, memory

PROBLEM DESCRIPTION
     The new MS780E memory controller will support a maximum of
     16 megabytes of physical memory but the kernel will only
     support at most 8 megabytes.

RESOLUTION
     The 8 megabyte restriction appears in two places.  First,
     the bit field sizes in the cmap structure are tuned to an 8
     megabyte maximum (exactly 13 bits).  Secondly, that portion
     of the assembly code support which discovers the total
     amount of available physical memory contains a hard coded 8
     megabyte limit.

     In cmap.h the bit fields c_next, c_prev and c_hlink must be
     increased in size from 13 to 14 bits and order of elements
     in the cmap structure must be rearranged to avoid crossing a
     word boundary in the middle of a field.  The new structure
     is:

     /*
      * core map entry
      */
     struct cmap
     {
     unsigned int  c_next:14,    /* index of next free list entry */
                   c_prev:14,    /* index of previous free list entry */
                   c_mdev:4,     /* which mounted dev this is from */
                   c_page:16,    /* virtual page number in segment */
                   c_hlink:14,   /* hash link for <blkno,mdev> */
                   c_type:2,     /* type CSYS or CTEXT or CSTACK or CDATA */
                   c_blkno:20,   /* disk block this is a copy of */
                   c_ndx:10,     /* index of owner proc or text */
                   c_lock:1,     /* locked for raw i/o or pagein */
                   c_want:1,     /* wanted */
                   c_intrans:1,  /* intransit bit */
                   c_free:1,     /* on the free list */
                   c_gone:1;     /* associated page has been released */
     };

     In locore.s change the code

         /* count up memory */

4.1bsd                    TRW (6/27/84)                         1

1984-0074             TRW/UNIX Modification             1984-0074

            clrl r7
         1: pushl $4; pushl r7; calls $2,_badaddr; tstl r0; bneq 9f
            acbl $8096*1024-1,$64*1024,r7,1b

     to

         /* count up memory */
            clrl r7
         1: pushl $4; pushl r7; calls $2,_badaddr; tstl r0; bneq 9f
            acbl $8096*1024*2-1,$64*1024,r7,1b
     allowing the kernel to count up to 16 megabytes of physical
     memory.

FILES
     /usr/src/sys/h/cmap.h         1.2
     /usr/include/sys/cmap.h       1.2
     /usr/src/sys/sys/locore.s     1.3

REQUESTOR
     Michael Gorlick

AUTHOR
     Michael Gorlick

REMARKS
     Similar changes must be made to go from 16 to 32 megabytes.
     However, for efficiency reasons, the constants of
     .../h/vmparam.h should also be resized.  Since a VAX 11/780
     or 785 doesn't have the raw speed to make good use of 32
     megabytes of memory it isn't worth the trouble now to
     accomodate the maximum memory configuration.

     Thanks to Lou Nelson, Aerospace who brought the problem to
     my attention and provided the definitive solution.

4.1bsd                    TRW (6/27/84)                         2