Date: Thu, 18 Sep 1997 06:18:59 PDT From: "Douglas Jardine" <djardine@hotmail.com> To: toor@dyson.iquest.net Cc: hackers@FreeBSD.ORG Subject: Re: LRU implementation Message-ID: <19970918131859.14824.qmail@hotmail.com>
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>From toor@dyson.iquest.net Mon Sep 15 13:02:41 1997 >> >None of the above. One way to describe it is "Not used recently >very often" :-). There are 2nd chance FIFO queues also. Umm. Can somebody please interpret this for me! I assume FreeBSD looks at the referenced bit to decide the "not used recently" part, but how does the "very often" part work? Where do the FIFO queues fit in the overall scheme? (If this is explained someplace a pointer will suffice). > >> >> The 4.3BSD book says that 4.3BSD uses 2-handed CLOCK but the 4.4BSD >> book is silent on this topic. Did FreeBSD diverge from 4.4BSD in >> this aspect? Does 4.4BSD use a 2-handed clock too? >> >FreeBSD is very different from 4.4BSD. As I remember, 4.4BSD is >a FIFO with 2nd chance. I am not very familiar with 2nd-Chance FIFOs so can somebody elaborate? As Joerg points out, on i386 the referenced bit is supported by hardware. But that by itself can't be used to construct a FIFO. So how is the FIFO formed? Once the FIFO is formed, I guess second chance would mean don't throw away the pages with referenced bit set. What is done with these pages - i.e. are they queued to the tail of the FIFO or left in place or ...? Thanks. -dj ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com
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