TECHNICAL INFORMATION DOCUMENT

TITLE:  TF2120 - Patch for Memory Paging Problems
DATE:  19SEP95
README FOR:  TF2120
PRODUCT and VERSION:

UnixWare 2.01

Installation Instructions:  

DATATYPE: datastream

1.  Download tf2120.Z and tf2120.txt to the /tmp directory      
    on your machine.

2.  Read the release notes contained in this file and follow the 
    instuctions to add the package to your system.

3.  Now become root, uncompress the file and add the package to your 
    system using the following commands:

        $ su
        # uncompress /tmp/tf2120.Z
        # pkgadd -d /tmp/tf2120

ENGINEERING RELEASE NOTES
-------------------------

Title
-----

PTF2120 - Patch for Memory Paging Problems 

Product And Version
-------------------

UnixWare 2.02

Abstract
--------

Changes to aging, cleaning, and recycling of pages of memory.

Symptom
--------

Under heavy loads, the system's processes may hang, or essentially become
idle, due to the inability to get free and clean memory pages.


SOLUTION SPECIFICS
------------------

General Description.
-------------------

With the elapsed time ager (ETA), a loop was developed whereby no
process could make forward progress because the pages it filled were
removed by the ETA before they were used.

The ETA is fixed by requiring it to skip processes that have failed to
accumulate CPU time since the last aging event.  Also, when more than
half of the CPU time is spent idle but with one or more processes
awaiting disk I/O completions, the ETA defers aging, since it only adds
to the I/O queues.

A second problem dealt with the excessively delayed recycling of dirty 
but free memory pages.  This problem is fixed by recognizing the need
for cleaning the dirty, free pages.  Using a new global called
"need_clean_pages".  the code can then selectively decide when to
free clean pages.

New Features.
------------

None

Software Notes and Recommendations.
----------------------------------

This PTF can be installed on UnixWare 2.02 systems.

Testing of the modified software contained in this package has
been conducted only to the extent necessary to confirm that it
resolves the problem(s) stated above ("Symptom").  Such testing
consists of recreating the problem conditions and verifying that 
the problem no longer occurs.  No other testing of this software 
has been done.

Hardware Notes and Recommendations.
----------------------------------

This PTF is targeted for the i386, i486 and Pentium CPU's.