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Add huge_page_size setting for use on Linux.

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This allows the huge page size to be set explicitly.  The default is 0,
meaning it will use the system default, as before.

Author: Odin Ugedal <odin@ugedal.com>
Discussion: https://postgr.es/m/20200608154639.20254-1-odin%40ugedal.com
This commit is contained in:
Thomas Munro
2020-07-17 14:33:00 +12:00
parent d66b23b032
commit d2bddc2500
6 changed files with 141 additions and 38 deletions
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27
doc/src/sgml/config.sgml
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@ -1582,6 +1582,33 @@ include_dir 'conf.d'
</listitem>
</varlistentry>
<varlistentry id="guc-huge-page-size" xreflabel="huge_page_size">
<term><varname>huge_page_size</varname> (<type>integer</type>)
<indexterm>
<primary><varname>huge_page_size</varname> configuration parameter</primary>
</indexterm>
</term>
<listitem>
<para>
Controls the size of huge pages, when they are enabled with
<xref linkend="guc-huge-pages"/>.
The default is zero (<literal>0</literal>).
When set to <literal>0</literal>, the default huge page size on the
system will be used.
</para>
<para>
Some commonly available page sizes on modern 64 bit server architectures include:
<literal>2MB</literal> and <literal>1GB</literal> (Intel and AMD), <literal>16MB</literal> and
<literal>16GB</literal> (IBM POWER), and <literal>64kB</literal>, <literal>2MB</literal>,
<literal>32MB</literal> and <literal>1GB</literal> (ARM). For more information
about usage and support, see <xref linkend="linux-huge-pages"/>.
</para>
<para>
Non-default settings are currently supported only on Linux.
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-temp-buffers" xreflabel="temp_buffers">
<term><varname>temp_buffers</varname> (<type>integer</type>)
<indexterm>

55
doc/src/sgml/runtime.sgml
View File

@ -1391,13 +1391,14 @@ export PG_OOM_ADJUST_VALUE=0
using large values of <xref linkend="guc-shared-buffers"/>. To use this
feature in <productname>PostgreSQL</productname> you need a kernel
with <varname>CONFIG_HUGETLBFS=y</varname> and
<varname>CONFIG_HUGETLB_PAGE=y</varname>. You will also have to adjust
the kernel setting <varname>vm.nr_hugepages</varname>. To estimate the
number of huge pages needed, start <productname>PostgreSQL</productname>
without huge pages enabled and check the
postmaster's anonymous shared memory segment size, as well as the system's
huge page size, using the <filename>/proc</filename> file system. This might
look like:
<varname>CONFIG_HUGETLB_PAGE=y</varname>. You will also have to configure
the operating system to provide enough huge pages of the desired size.
To estimate the number of huge pages needed, start
<productname>PostgreSQL</productname> without huge pages enabled and check
the postmaster's anonymous shared memory segment size, as well as the
system's default and supported huge page sizes, using the
<filename>/proc</filename> and <filename>/sys</filename> file systems.
This might look like:
<programlisting>
$ <userinput>head -1 $PGDATA/postmaster.pid</userinput>
4170
@ -1405,27 +1406,40 @@ $ <userinput>pmap 4170 | awk '/rw-s/ &amp;&amp; /zero/ {print $2}'</userinput>
6490428K
$ <userinput>grep ^Hugepagesize /proc/meminfo</userinput>
Hugepagesize: 2048 kB
$ <userinput>ls /sys/kernel/mm/hugepages</userinput>
hugepages-1048576kB hugepages-2048kB
</programlisting>
In this example the default is 2MB, but you can also explicitly request
either 2MB or 1GB with <xref linkend="guc-huge-page-size"/>.
Assuming <literal>2MB</literal> huge pages,
<literal>6490428</literal> / <literal>2048</literal> gives approximately
<literal>3169.154</literal>, so in this example we need at
least <literal>3170</literal> huge pages, which we can set with:
least <literal>3170</literal> huge pages. A larger setting would be
appropriate if other programs on the machine also need huge pages.
We can set this with:
<programlisting>
$ <userinput>sysctl -w vm.nr_hugepages=3170</userinput>
# <userinput>sysctl -w vm.nr_hugepages=3170</userinput>
</programlisting>
A larger setting would be appropriate if other programs on the machine
also need huge pages. Don't forget to add this setting
to <filename>/etc/sysctl.conf</filename> so that it will be reapplied
after reboots.
Don't forget to add this setting to <filename>/etc/sysctl.conf</filename>
so that it is reapplied after reboots. For non-default huge page sizes,
we can instead use:
<programlisting>
# <userinput>echo 3170 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages</userinput>
</programlisting>
It is also possible to provide these settings at boot time using
kernel parameters such as <literal>hugepagesz=2M hugepages=3170</literal>.
</para>
<para>
Sometimes the kernel is not able to allocate the desired number of huge
pages immediately, so it might be necessary to repeat the command or to
reboot. (Immediately after a reboot, most of the machine's memory
should be available to convert into huge pages.) To verify the huge
page allocation situation, use:
pages immediately due to fragmentation, so it might be necessary
to repeat the command or to reboot. (Immediately after a reboot, most of
the machine's memory should be available to convert into huge pages.)
To verify the huge page allocation situation for a given size, use:
<programlisting>
$ <userinput>grep Huge /proc/meminfo</userinput>
$ <userinput>cat /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages</userinput>
</programlisting>
</para>
@ -1438,8 +1452,9 @@ $ <userinput>grep Huge /proc/meminfo</userinput>
<para>
The default behavior for huge pages in
<productname>PostgreSQL</productname> is to use them when possible and
to fall back to normal pages when failing. To enforce the use of huge
<productname>PostgreSQL</productname> is to use them when possible, with
the system's default huge page size, and
to fall back to normal pages on failure. To enforce the use of huge
pages, you can set <xref linkend="guc-huge-pages"/>
to <literal>on</literal> in <filename>postgresql.conf</filename>.
Note that with this setting <productname>PostgreSQL</productname> will fail to