Date: Tue, 28 Apr 2020 02:28:48 +0000 (UTC) From: Allan Jude <allanjude@FreeBSD.org> To: doc-committers@freebsd.org, svn-doc-all@freebsd.org, svn-doc-head@freebsd.org Subject: svn commit: r54079 - head/en_US.ISO8859-1/books/faq Message-ID: <202004280228.03S2SmXq076378@repo.freebsd.org>
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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: pauamma@gundo.com 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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