Reducing bufcache on AdvFS only systems

From: John P. Speno <speno_at_swarthmore.edu>
Date: Wed, 12 Mar 1997 13:43:45 -0500

In reading the System Tuning and Performance Management manual here:

http://www.UNIX.digital.com/faqs/publications/base_doc/DOCUMENTATION/HTML/AA-Q0R3E-TET1_html/TITLE.html

Specifically, in the section called "3.4.1.3 Tailoring Usage of Metadata and
Namei Buffer Caches" here:

http://www.UNIX.digital.com/faqs/publications/base_doc/DOCUMENTATION/HTML/AA-Q0R3E-TET1_html/tune4.html#tune_metadata_section

(sorry for the long URL's)

We are told that the kernel variable "bufcache" controls the percentage of
system memory allocated to the kernel's metadata buffer cache. We are also
told that AdvFS does not use this cache, as it has its own (See:
http://www.UNIX.digital.com/faqs/publications/base_doc/DOCUMENTATION/HTML/AA-Q0R3E-TET1_html/tune6.html#advfs_subsystem
for the minimal AdvFS section)

Therefore, on systems that do not have any UFS file systems, shouldn't we be
able to reduce 'bufcache' (default is 3, or 2 on systems with mem < 24MB) to
a lower value without seriously impacting system performance?

Furthermore, when the system displays this upon startup:

        physical memory = 512.00 megabytes.
        available memory = 496.14 megabytes.
        using 1958 buffers containing 15.29
         _megabytes of memory

Is that "available memory" referring to the amount left over after the 3
percent chunk allocated for the 'bufcache'? If you do the math, it's damn
close to 3% anyway.

Thanks.

-- 
John P. Speno, speno_at_swarthmore.edu, Swarthmore College Computing Center
	    "There is no wisdom greater than kindness."

Received on Wed Mar 12 1997 - 20:00:54 NZDT