svn commit: r54079 - head/en_US.ISO8859-1/books/faq

Author: allanjude
Date: Tue Apr 28 02:28:48 2020
New Revision: 54079
URL: https://svnweb.freebsd.org/changeset/doc/54079

Log:
  Update FAQ entries 10.21 and 10.22
  
  PR:		242062
  Submitted by:	[email protected]
  Reviewed by:	markj, debdrup
  Differential Revision:	https://reviews.freebsd.org/D24486

Modified:
  head/en_US.ISO8859-1/books/faq/book.xml

Modified: head/en_US.ISO8859-1/books/faq/book.xml
==============================================================================
--- head/en_US.ISO8859-1/books/faq/book.xml	Tue Apr 28 00:32:38 2020	(r54078)
+++ head/en_US.ISO8859-1/books/faq/book.xml	Tue Apr 28 02:28:48 2020	(r54079)
@@ -4003,7 +4003,7 @@ options    SYSVMSG          # enable for messaging</pr
 	    <command>top</command> mean?</para>
 	</question>
 
-	<!-- Provided by John Dyson via Usenet -->
+	<!-- Provided by John Dyson via Usenet, and later amended -->
 	<answer>
 	  <itemizedlist>
 	    <listitem>
@@ -4017,24 +4017,15 @@ options    SYSVMSG          # enable for messaging</pr
 	    </listitem>
 
 	    <listitem>
-	      <para><literal>Cache</literal>: (most often) pages that
-		have percolated from inactive to a status where they
-		maintain their data, but can often be immediately
-		reused (either with their old association, or reused
-		with a new association).  There can be certain
-		immediate transitions from <literal>active</literal>
-		to <literal>cache</literal> state if the page is known
-		to be clean (unmodified), but that transition is a
-		matter of policy, depending upon the algorithm choice
-		of the VM system maintainer.</para>
+	      <para><literal>Laundry</literal>: pages recently
+		statistically unused but known to be dirty, that is,
+                whose contents needs to be paged out before they can
+		be reused.</para>
 	    </listitem>
 
 	    <listitem>
 	      <para><literal>Free</literal>: pages without data
-		content, and can be immediately used in certain
-		circumstances where cache pages might be ineligible.
-		Free pages can be reused at interrupt or process
-		state.</para>
+		content, which can be immediately reused.</para>
 	    </listitem>
 
 	    <listitem>
@@ -4045,21 +4036,19 @@ options    SYSVMSG          # enable for messaging</pr
 	  </itemizedlist>
 
 	  <para>Pages are most often written to disk (sort of a VM
-	    sync) when they are in the inactive state, but active
-	    pages can also be synced.  This depends upon the CPU
-	    tracking of the modified bit being available, and in
+	    sync) when they are in the laundry state, but active or
+	    inactive pages can also be synced.  This depends upon the
+	    CPU tracking of the modified bit being available, and in
 	    certain situations there can be an advantage for a block
-	    of VM pages to be synced, whether they are active or
-	    inactive.  In most common cases, it is best to think of
-	    the inactive queue to be a queue of relatively unused
+	    of VM pages to be synced, regardless of the queue they
+	    belong to.  In most common cases, it is best to think of
+	    the laundry queue as a queue of relatively unused
 	    pages that might or might not be in the process of being
-	    written to disk.  Cached pages are already synced, not
-	    mapped, but available for immediate process use with their
-	    old association or with a new association.  Free pages are
-	    available at interrupt level, but cached or free pages can
-	    be used at process state for reuse.  Cache pages are not
-	    adequately locked to be available at interrupt
-	    level.</para>
+	    written to disk.  The inactive queue contains a mix of
+	    clean and dirty pages; clean pages near the head of the
+	    queue are reclaimed immediately to alleviate a free page
+	    shortage, and dirty pages are moved to the laundry queue
+	    for deferred processing.</para>
 
 	  <para>There are some other flags (e.g., busy flag or busy
 	    count) that might modify some of the described
@@ -4072,17 +4061,19 @@ options    SYSVMSG          # enable for messaging</pr
 	  <para>How much free memory is available?</para>
 	</question>
 
-	<!-- Provided by John Dyson via Usenet -->
+	<!-- Provided by John Dyson via Usenet, and later amended -->
 	<answer>
 	  <para>There are a couple of kinds of <quote>free
-	      memory</quote>.  One kind is the amount of memory
-	    immediately available without paging anything else out.
-	    That is approximately the size of cache queue + size of
-	    free queue (with a derating factor, depending upon system
-	    tuning).  Another kind of <quote>free memory</quote> is
-	    the total amount of <acronym>VM</acronym> space.  That can
-	    be complex, but is dependent upon the amount of swap space
-	    and memory.  Other kinds of <quote>free memory</quote>
+	    memory</quote>.  The most common is the amount of memory
+	    immediately available without reclaiming memory already
+	    in use.  That is the size of the free pages queue plus
+	    some other reserved pages.  This amount is exported by the
+	    <literal>vm.stats.vm.v_free_count</literal>
+	    &man.sysctl.8;, shown, for instance, by &man.top.1;.
+	    Another kind of <quote>free memory</quote> is
+	    the total amount of virtual memory available to userland
+	    processes, which depends on the sum of swap space and
+	    usable memory.  Other kinds of <quote>free memory</quote>
 	    descriptions are also possible, but it is relatively
 	    useless to define these, but rather it is important to
 	    make sure that the paging rate is kept low, and to avoid
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