muller@sdcc3.UUCP (Keith Muller) (12/30/84)
Index: sys/sys/vm_sched.c sys/vax/vmparam.h 4.2BSD
Description:
At boot time 4.2 will size the paging point and swapping point
according to the amount of free main memory is available. The
algorithim used for sizing lotsfree (the paging point) does not
have an upper bound, but always sets the paging point to be 1/4
of free memory. This can be quite a large value for machines with
with greater than around 3 megabytes of main memory (with memory
prices getting lower, machines with more than 4 megs are quite common).
This is a real performance problem in these large memory machines
as they will begin paging when the machine is not even close to
running out of memory. This premature paging begins to use up
cpu cycles causing the machines throughput to rapidly decline (and
also tends to offset any gains obtained by increasing the amount
of main memory a machine might have).
The swapping point maximium (desfree) is set a bit too large.
Repeat-By:
Load up your machine with a lot of memory intensive programs and watch
the virtual memory system with a vmstat 3. The sr (scan rate) should
always be as small as possible to maximize throughput (scanning costs
cpu cycles). The fr value (free memory) indicates the size of free
memory in the system. On large memory machines the sr can be quite
high (100 or more) with 1 megabyte (or more) of main memory free.
Fix:
The fix has two parts:
1) adding a new #define to vax/vmparam.h for the maximium limit on
lotsfree and changing the swapping point.
2) changing the code in sys/vm_sched.c that sizes lotsfree.
The diffs are below:
RCS file: RCS/vmparam.h,v
retrieving revision 1.1
diff -c -r1.1 vmparam.h
*** /tmp/,RCSt1029938 Sat Dec 29 15:16:36 1984
--- vmparam.h Sat Dec 29 14:31:03 1984
***************
*** 97,105
/*
* Paging thresholds (see vm_sched.c).
! * Strategy of 4/22/81:
! * lotsfree is 1/4 of memory free.
! * desfree is 200k bytes, but at most 1/8 of memory
* minfree is 64k bytes, but at most 1/2 of desfree
*/
#define LOTSFREEFRACT 4
--- 97,105 -----
/*
* Paging thresholds (see vm_sched.c).
! * Strategy of 9/28/84:
! * lotsfree is 512k bytes, but at most 1/4 of memory
! * desfree is 128k bytes, but at most 1/8 of memory
* minfree is 64k bytes, but at most 1/2 of desfree
*/
#define LOTSFREE (512 * 1024)
***************
*** 102,107
* desfree is 200k bytes, but at most 1/8 of memory
* minfree is 64k bytes, but at most 1/2 of desfree
*/
#define LOTSFREEFRACT 4
#define DESFREE (200 * 1024)
#define DESFREEFRACT 8
--- 102,108 -----
* desfree is 128k bytes, but at most 1/8 of memory
* minfree is 64k bytes, but at most 1/2 of desfree
*/
+ #define LOTSFREE (512 * 1024)
#define LOTSFREEFRACT 4
#define DESFREE (128 * 1024)
#define DESFREEFRACT 8
***************
*** 103,109
* minfree is 64k bytes, but at most 1/2 of desfree
*/
#define LOTSFREEFRACT 4
! #define DESFREE (200 * 1024)
#define DESFREEFRACT 8
#define MINFREE (64 * 1024)
#define MINFREEFRACT 2
--- 104,110 -----
*/
#define LOTSFREE (512 * 1024)
#define LOTSFREEFRACT 4
! #define DESFREE (128 * 1024)
#define DESFREEFRACT 8
#define MINFREE (64 * 1024)
#define MINFREEFRACT 2
--------------------------------------------------------------------
RCS file: RCS/vm_sched.c,v
retrieving revision 1.1
diff -c -r1.1 vm_sched.c
*** /tmp/,RCSt1029948 Sat Dec 29 15:17:11 1984
--- vm_sched.c Sat Dec 29 14:44:32 1984
***************
*** 55,61
* tolerable.
*/
if (lotsfree == 0)
! lotsfree = LOOPPAGES / LOTSFREEFRACT;
if (desfree == 0) {
desfree = DESFREE / NBPG;
if (desfree > LOOPPAGES / DESFREEFRACT)
--- 55,63 -----
* tolerable.
*/
if (lotsfree == 0)
! lotsfree = LOTSFREE / NBPG;
! if (lotsfree > LOOPPAGES / LOTSFREEFRACT)
! lotsfree = LOOPPAGES / LOTSFREEFRACT;
if (desfree == 0) {
desfree = DESFREE / NBPG;
if (desfree > LOOPPAGES / DESFREEFRACT)
---------------------------------------------------------------------
Keith Muller
University of California, San Diego
Academic Computer Center
ucbvax!sdcsvax!muller
muller@nprdcchris@umcp-cs.UUCP (Chris Torek) (01/03/85)
Looks like you missed a set of braces (else your indentation is wrong):
diff -c -r1.1 vm_sched.c
.
.
.
--- 55,63 -----
* tolerable.
*/
if (lotsfree == 0)
! lotsfree = LOTSFREE / NBPG;
! if (lotsfree > LOOPPAGES / LOTSFREEFRACT)
! lotsfree = LOOPPAGES / LOTSFREEFRACT;
if (desfree == 0) {
desfree = DESFREE / NBPG;
if (desfree > LOOPPAGES / DESFREEFRACT)
should probably be
if (lotsfree == 0) {
lotsfree = LOTSFREE / NBPG
if (lotsfree > LOOPPAGES / LOTSFREEFRACT)
lotsfree = LOOPPAGES / LOTSFREEFRACT;
}
This way the fraction is ignored if you set lotsfree with adb.
--
(This line accidently left nonblank.)
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (301) 454-7690
UUCP: {seismo,allegra,brl-bmd}!umcp-cs!chris
CSNet: chris@umcp-cs ARPA: chris@marylandmuller@sdcc3.UUCP (Keith Muller) (01/05/85)
> Index: sys/sys/vm_sched.c sys/vax/vmparam.h 4.2BSD > > Description: > At boot time 4.2 will size the paging point and swapping point > according to the amount of free main memory is available. The > algorithim used for sizing lotsfree (the paging point) does not > ..... The submitted fix was missing a pair of {}. The correct fix is: RCS file: RCS/vm_sched.c,v retrieving revision 1.1 diff -c -r1.1 vm_sched.c *** /tmp/,RCSt1001834 Tue Jan 1 14:56:27 1985 --- vm_sched.c Tue Jan 1 14:53:22 1985 *************** *** 54,61 * minfree is minimal amount of free memory which is * tolerable. */ ! if (lotsfree == 0) ! lotsfree = LOOPPAGES / LOTSFREEFRACT; if (desfree == 0) { desfree = DESFREE / NBPG; if (desfree > LOOPPAGES / DESFREEFRACT) --- 54,64 ----- * minfree is minimal amount of free memory which is * tolerable. */ ! if (lotsfree == 0){ ! lotsfree = LOTSFREE / NBPG; ! if (lotsfree > LOOPPAGES / LOTSFREEFRACT) ! lotsfree = LOOPPAGES / LOTSFREEFRACT; ! } if (desfree == 0) { desfree = DESFREE / NBPG; if (desfree > LOOPPAGES / DESFREEFRACT) Sorry for the error, i made a keystroke error while checking in the rcs file. Keith Muller University of California Academic Computer Center