From:	ian AT cygnus DOT com
Subject:	Re: Time and motion studies of gcc and egcs and LCC
4 Feb 1998 16:59:48 -0800 :
Message-ID:	<199802041912.OAA07512.cygnus.gnu-win32@tweedledumb.cygnus.com>
References:	<004701bd30c0$77196910$2a0110ac AT sam DOT ethernet>
To:	sam AT campbellsci DOT co DOT uk
Cc:	gnu-win32 AT cygnus DOT com

In gnu-win32 sam AT campbellsci DOT co DOT uk (Samuel James Liddicott) writes:

>I read that in win95 the pages are flushed in order of first-in-first-out,
>and if a flushed page is a commonly used page, it will just be first-in
>again a bit quicker, and all this to save on the overheads of working out
>which pages are least used.

>I was shocked when I read it too, but imagine the overheads of doing page
>usage sorting every time you need to load a new page?  MS seemed to think
>little was gained.

There are several other approaches.  One technique is to have a daemon
which periodically marks pages as unreadable and unwritable.  When
there is an exception on the page, the protection is removed, and the
page is moved to the end of usage list.  This way the pages are very
roughly sorted by usage when it comes time to discard a page.

Discarding pages in strict FIFO order seems to me like a recipe for
thrashing.

Ian
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