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Date:      Wed, 22 Sep 1999 11:27:56 -0600
From:      Nate Williams <nate@mt.sri.com>
To:        Alfred Perlstein <bright@wintelcom.net>
Cc:        Chuck Robey <chuckr@mat.net>, "Daniel C. Sobral" <dcs@newsguy.com>, Ivan <Ivan.Djelic@prism.uvsq.fr>, Matthew Dillon <dillon@apollo.backplane.com>, freebsd-hackers@FreeBSD.ORG
Subject:   Re: Out of swap handling and X lockups in 3.2R
Message-ID:  <199909221727.LAA14290@mt.sri.com>
In-Reply-To: <Pine.BSF.4.05.9909221024370.6368-100000@fw.wintelcom.net>
References:  <Pine.BSF.4.10.9909221227080.312-100000@picnic.mat.net> <Pine.BSF.4.05.9909221024370.6368-100000@fw.wintelcom.net>

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> > What kind of resources are there that both cause loss of swap AND are
> > freed up by sleeping a process?
> 
> four things i can think of:
> 
> 1) Along with 'SIGDANGER' it allows the system to fix itself.

That's another issue.  Don't mix sleeping processes with SIGDANGER, they
are independant of one another.
There's no mention of SIGDANGER, just of pu

> 2) Allow the operator to determine which program to kill, maybe the
>    'hog' is actually something that needs to run to completion and
>    by shutting down other systems it would survive.

The operator can't kill anything, since the system would be unusable at
that point, being out of resources and all.  His shell wouldn't even
run.

> 3) other processes may exit, this would free the memory needed to
>    continue.

Maybe, and then again, maybe not.  A program is requesting memory, so
putting other processes to sleep *keeps* them from freeing up memory.

> 4) the operator could enable swap on an additional device giving
>    more backing for things to continue.

See above.  There are no resources available for anything to run, so the
system must do *SOMETHING*.

(Yes, this is a problem with memory-overcommit, but them's the
breaks. :)


Nate


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