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Pastimes : Dream Machine ( Build your own PC ) -- Ignore unavailable to you. Want to Upgrade?

To: Sean W. Smith who wrote (3561)	11/16/1998 12:01:00 PM
From: Spots	Read Replies (1) \| Respond to of 14778

>>you are very correct... Sounds to me like you're saying I'm incorrect <gg>. Could such a thing be so? Ok, I admit my info on virtual memory implementation is getting a bit dated, but this surprises me, more than just a little. How do you avoid writing clean pages on a page fault? Any unmapped page has to be mapped then written, which essentially means any page fault is a dirty page fault. (An exception for program files, assuming code is pure: The OS can always page against the program object.) EDIT: The preceding paragraph is essentially gibberish. What I was trying to convey was that if there are fewer pages in the swap space than in the virtual memory space, then when the swap space gets full in order to map a new page you have to unmap an existing page to free up room in the swap space. The newly unmapped page remains in memory (it has nowhere else to go if you take its swap space away), but it's automatically dirty, even if it was clean before. You could dirty a lot of clean laundry that way <gg>. Seems to me the laundry bill would be high. Those are VERY clever algorithms to surmount that. End edit. Lot's of OSs don't do static mapping of segments, so I've missed your point on that comment. I never meant to imply that page/segment mapping is static, just that it occurs when the page is allocated to a process or possibly on the FIRST time it's paged out, which can make a very efficient algorithm. Either strategy means the pageable virtual memory is essentially the same size as the swap space.