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From: marc@dumbcat.sf.ca.us (Marco S Hyman)
Newsgroups: comp.unix.sysv386
Subject: Re: out of swap space??
Message-ID: <296@dumbcat.sf.ca.us>
Date: 28 Apr 91 19:36:47 GMT
References: <1991Apr23.214037.16410@netcom.COM> <1991Apr24.123035.4193@virtech.uucp> <455@jgaltstl.UUCP>
Organization: MH Software, Hayward, CA.
Lines: 25

In article <455@jgaltstl.UUCP> terry@jgaltstl.UUCP (terry linhardt) writes:
 > I've often wondered where the recommendation that 2 - 3x real memory should
 > be made available to swap comes from? Wouldn't this depend upon
 > whether or not the system is swapping at all? For instance, let's
 > say you have 48 meg of memory, and no swapping. Does this mean
 > I should tie up 100 - 150 meg of disk space for swap?

Hmmm.  I seem to remember that Berkeley UNIX allocates swap space at exec time
to ensure a process can be swapped out later. (I can't verify this right
now... it may be a false statement.)  If true, you'll have to allocate that
disk space even if it's never used.  I just looked thru Bach's "The Design of
the UNIX Operating System" and don't see a similar requirement for System V.
I wonder about System V Release 4, though.  Does anybody know?

 >  Also, isn't there less need for swap space with paging systems?

When a process is swapped only the active pages are written to the swap
device.  The swapped out process is placed in a state "ready to run but
swapped."  These processes are not swapped back into memory in their entirety
-- they are allowed to page fault back in off of the swap device.

-- 
// marc
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