Sun Microsystems Sun Workstation 100U System Manager's Manual page 293

Data Structure Sizing Rules
Building Sun \Vorkstation Kernels
ndquot
The number of "dquot" structures allocated. Dquot structures are present only when disc
quotas are configured in the system. One dquot structure is required per user, per active file
system quota. That is, when a user manipulates a file on a file system on which quotas are
enabled, the information regarding the user's quotas on that file system must be in-core.
This information is cached, so that not all information must be present in-core all the time.
This is defined
as
(MAXUSERS
*
NMOUNT) /
4
+
NPROC, where NMOUNT is the max-
imum number of mountable file systems.
D.2. Run-time Calculations
The most important data structure sized at run-time is the file system buffer cache. The system
allocates 10% of each half-megabyte after the first half-megabyte to the cache. Thus on a 1
Megabyte machine, 50 kilobytes is allocated to the cache, while on a 2 Megabyte machine, 150
kilobytes is allocated to the cache. In any case, not less than 16 pages of file system bufIef5 is
allocated.
The number of buffers to be allocated can be forced to a specific value by patching the kernel
variable nbufwith adb:
#=
adb -w Ivmunix
nbuf!W Ot32
nbuf: 0
=
20
$q
#=
sets the number of buffers to be 32 (decimal) independent of the amount of main memory avail-
able. Reboot after performing this series.
D.3. System Size Limitations
Because the file system block numbers are stored in page table pg_blkno entries, the maximum
size of a file system is limited to 2" 19 1024 byte blocks. Thus no file system can be larger than
512M bytes.
The count of mountable file systems is limited to 15. This should be sufficient. If you have
many disks it makes sense to make some of them single file systems, and the paging areas don't
count in this total. To increase this, you must change the core-map (only if you have source)
/
~Y~I
hI cmap.h, since there is a 4 bit field used here. The size of the core-map will then expand
to 16 bytes per 2048 byte page. Don't forget to change MSWAPX and
N~10UNT
in
I
~Y81
hI param.h also.
The maximum value NOFILE (open files per process limit) can be raised to is 30 because of a
bit field in the page table entry in I
'y'l
machine/ pte.h.
22
7 January 1984