Swapping and wmgr

[Michael Ditto]

In article <459 at bacchus> darren at bacchus.UUCP (Darren Friedlein) writes:
>In article <153 at elgar.UUCP> ford at kenobi.UUCP (Mike Ditto) writes:
>>In article <449 at bacchus> darren at bacchus (Darren Friedlein) writes:
>>>I have a question that I'm hoping someone can answer... I run phdaemon on
>>>my machine and when memory has to be swapped out to disk, phdaemon fails,
>>>leaves me a message under the [!!] icon and I re-start it.
>>
>>What is the message?  How do you know it has anything to do with
>>swapping (and do you really mean swapped, as in a "0" Flags entry in
>>ps -fl, or just normal VM paging)?
>
>When smgr (found out I had the wrong mgr) displayed the [!!] icon before,
>the message I got was that phdaemon died because SOMETHING was swapped
>out, either phdaemon or a program it was monitoring.

Ahh... I'm beginning to understand the setup... I had no idea that
phdaemon was such a sneaky program as to go peeking at other processes'
user information.  So what happened is phdaemon tried to look at the
user structure for something (probably the /etc/ph process) and found
that it was not in memory.  Phdaemon's author (isn't that you, Lenny?)
didn't provide for this situation and had the program exit instead
(probably based on the first version of "fuser", which did the same
thing).

>  This time, smgr
>quit completely right after the [!!] icon appeared.  From ps, I could
>see that the system load was real heavy.  This doesn't assure that
>swapping was the cause, but that would be my best guess.

I would guess that that was not directrly related, unless phdaemon is
sending some weird stuff to the smgr.  Perhaps you ran out of swap
space.

>What is the difference between a process being swapped out and normal
>VM paging?  I thought the UNIXpc could only support 4M or virtual memory,
>but when I formatted the drive, it reserved 6M of space.

Normally, individual pages of memory are moved to the swap device when they
aren't needed, and brought back in individually when something tries to use
them.  Processes are "swapped out" when the system gets desparate for space.
A swapped process is completely stored on disk and can not execute at all
until it is (at least partially) swapped in.  If a process is swapped out,
bit zero of the "F" field of the ps display will be zero.

The Unix PC supports 4M of virtual memory PER PROCESS, with a total amount
dependant on your physical memory + swap space.

By the way, Unix completely hides the whole questions of swapping and
paging from user programs.  It's only in the rare case of a weird program
like ps, fuser, or (apparrently) phdaemon that it comes up.  That's why
I was really surprised to hear someone claim that they were getting errors
because of swapping.

-- 

Mike Ditto					-=] Ford [=-
P.O. Box 1721					ford%kenobi at crash.CTS.COM
Bonita, CA 92002				ford at crash.CTS.COM