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Date:      Sun, 05 Apr 1998 17:26:40 -0400
From:      Dan Swartzendruber <dswartz@druber.com>
To:        dg@root.com
Cc:        dag-erli@ifi.uio.no (Dag-Erling Coidan =?iso-8859-1?Q?Sm=F8rgrav?= ), stable@FreeBSD.ORG, current@FreeBSD.ORG
Subject:   Re: swap-leak in 2.2.5 ? 
Message-ID:  <3.0.5.32.19980405172640.00915e30@mail.kersur.net>
In-Reply-To: <199804052022.NAA11264@implode.root.com>
References:  <Your message of "05 Apr 1998 18:13:06 %2B0200."             <xzplntk6yct.fsf@hrotti.ifi.uio.no>

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At 01:22 PM 4/5/98 -0700, David Greenman wrote:
>>while. It's simply a *lot* faster to keep already-linked executables
>>in memory (and move them into swap when memory goes full) rather than
>>throwing them out and having to reload and relink them next time they
>>are invoked, as long as they haven't changed in the meantime.
>>
>>David, I hope my explanation is not too far off?
>
>   Actually, it's not that the system has to do any re-linking. The reason
>that swap space is consumed even when you have plenty of memory is that the
>system also tries to cache regular file data, so freeing up memory for that
>by moving modified but not recently used process pages to swap is usually a
>good thing.

My only quibble with this technique is that it would seem to make it
harder to tell if your machine is really running low on swap or not
(e.g. swap as backing store for stack/heap/whatever *is* critical and
allocation failure can cause application failure, whereas swap being
used to cache random cruft is in the "who really cares" department).
Or is there some way to tell the difference?




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