diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/config.sgml | 24 | ||||
| -rw-r--r-- | doc/src/sgml/runtime.sgml | 51 |
2 files changed, 61 insertions, 14 deletions
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index cf11306f6cb..065c1dbdcf0 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -1166,35 +1166,31 @@ include 'filename' </listitem> </varlistentry> - <varlistentry id="guc-huge-tlb-pages" xreflabel="huge_tlb_pages"> - <term><varname>huge_tlb_pages</varname> (<type>enum</type>)</term> + <varlistentry id="guc-huge-pages" xreflabel="huge_pages"> + <term><varname>huge_pages</varname> (<type>enum</type>)</term> <indexterm> - <primary><varname>huge_tlb_pages</> configuration parameter</primary> + <primary><varname>huge_pages</> configuration parameter</primary> </indexterm> <listitem> <para> - Enables/disables the use of huge TLB pages. Valid values are + Enables/disables the use of huge memory pages. Valid values are <literal>try</literal> (the default), <literal>on</literal>, and <literal>off</literal>. </para> <para> - At present, this feature is supported only on Linux. The setting - is ignored on other systems. + At present, this feature is supported only on Linux. The setting is + ignored on other systems when set to <literal>try</literal>. </para> <para> - The use of huge TLB pages results in smaller page tables and - less CPU time spent on memory management, increasing performance. For - more details, see - <ulink url="https://wiki.debian.org/Hugepages">the Debian wiki</ulink>. - Remember that you will need at least shared_buffers / huge page size + - 1 huge TLB pages. So for example for a system with 6GB shared buffers - and a hugepage size of 2kb of you will need at least 3156 huge pages. + The use of huge pages results in smaller page tables and less CPU time + spent on memory management, increasing performance. For more details, + see <xref linkend="linux-huge-pages">. </para> <para> - With <varname>huge_tlb_pages</varname> set to <literal>try</literal>, + With <varname>huge_pages</varname> set to <literal>try</literal>, the server will try to use huge pages, but fall back to using normal allocation if that fails. With <literal>on</literal>, failure to use huge pages will prevent the server from starting up. With diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml index bbb808fecb0..7f4a2358c45 100644 --- a/doc/src/sgml/runtime.sgml +++ b/doc/src/sgml/runtime.sgml @@ -1307,6 +1307,57 @@ echo -1000 > /proc/self/oom_score_adj </para> </note> </sect2> + + <sect2 id="linux-huge-pages"> + <title>Linux huge pages</title> + + <para> + Using huge pages reduces overhead when using large contiguous chunks of + memory, like <productname>PostgreSQL</productname> does. To enable this + feature in <productname>PostgreSQL</productname> you need a kernel + with <varname>CONFIG_HUGETLBFS=y</varname> and + <varname>CONFIG_HUGETLB_PAGE=y</varname>. You also have to tune the system + setting <varname>vm.nr_hugepages</varname>. To estimate the number of + necessary huge pages start <productname>PostgreSQL</productname> without + huge pages enabled and check the <varname>VmPeak</varname> value from the + proc filesystem: +<programlisting> +$ <userinput>head -1 /path/to/data/directory/postmaster.pid</userinput> +4170 +$ <userinput>grep ^VmPeak /proc/4170/status</userinput> +VmPeak: 6490428 kB +</programlisting> + <literal>6490428</literal> / <literal>2048</literal> + (<varname>PAGE_SIZE</varname> is <literal>2MB</literal> in this case) are + roughly <literal>3169.154</literal> huge pages, so you will need at + least <literal>3170</literal> huge pages: +<programlisting> +$ <userinput>sysctl -w vm.nr_hugepages=3170</userinput> +</programlisting> + Sometimes the kernel is not able to allocate the desired number of huge + pages, so it might be necessary to repeat that command or to reboot. Don't + forget to add an entry to <filename>/etc/sysctl.conf</filename> to persist + this setting through reboots. + </para> + + <para> + The default behavior for huge pages in + <productname>PostgreSQL</productname> is to use them when possible and + to fallback to normal pages when failing. To enforce the use of huge + pages, you can set + <link linkend="guc-huge-pages"><varname>huge_pages</varname></link> + to <literal>on</literal>. Note that in this case + <productname>PostgreSQL</productname> will fail to start if not enough huge + pages are available. + </para> + + <para> + For a detailed description of the <productname>Linux</productname> huge + pages feature have a look + at <ulink url="https://www.kernel.org/doc/Documentation/vm/hugetlbpage.txt">https://www.kernel.org/doc/Documentation/vm/hugetlbpage.txt</ulink>. + </para> + + </sect2> </sect1> |