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From: rcd@ico.isc.com (Dick Dunn)
Newsgroups: comp.unix.i386
Subject: Re: 386 Motherboards (and paging, swapping, copying)
Summary: terminology (paging, swapping)
Message-ID: <1990May5.004337.6277@ico.isc.com>
Date: 5 May 90 00:43:37 GMT
References: <607@ssp2.idca.tds.philips.nl>
Organization: Interactive Systems Corporation, Boulder, CO
Lines: 28

pb@idca.tds.PHILIPS.nl (Peter Brouwer) writes:

> In a paging system pages are loaded on demand and if memory gets thight
> pages are swapped.

This is a confusion of terms.  "Paging" refers to movement of individual
pages from a process.  To avoid confusion, the process of cleaning a page--
that is, writing out the contents of a modified page frame so that it can
be reused to "page in" something else--is normally called a "pageout".

That way, "swapping" can be used to refer to wholesale movement of
processes in/out of memory:  When memory commitment gets too high, you can
"swap out" a process--meaning to remove ALL of its pages from physical
memory.

> If a page is swapped out or in it is copied through a few buffers in memory
> in the kernel code. Like from the memory from the disk controller into a
> kernel buffer and from that to the location in memory where it will be used.

No, pages don't go through the buffer cache.  The page goes, in effect,
between the disk controller (which, although it may be "memory", is not
system memory and is not subject to the main memory-system caching) and
the physical memory where it belongs.  Thus this only affects caching to
the extent that bringing in a page replaces any cached locations for that
page--which is just what you want.
-- 
Dick Dunn     rcd@ico.isc.com    uucp: {ncar,nbires}!ico!rcd     (303)449-2870
   ...Lately it occurs to me what a long, strange trip it's been.