[PATCH] Add support for choosing huge page size

This adds support for using non-default huge page sizes for shared
memory. This is achived via the new "huge_page_size" config entry.
The config value defaults to 0, meaning it will use the system default.
---

This would be very helpful when running in kubernetes since nodes may
support multiple huge page sizes, and have pre-allocated huge page meory
for each size. This lets the user select huge page size without having
to change the default huge page size on the node. This will also be
useful when doing benchmarking with different huge page sizes, since it
wouldn't require a full system reboot.

Since the default value of the new config is 0 (resulting in using the
default huge page size) this should be backwards compatible with old
configs.

Feel free to comment on the phrasing (both in docs and code) and on the
overall change.

doc/src/sgml/config.sgml | 25 ++++++
doc/src/sgml/runtime.sgml | 41 +++++----
src/backend/port/sysv_shmem.c | 88 ++++++++++++-------
src/backend/utils/misc/guc.c | 11 +++
src/backend/utils/misc/postgresql.conf.sample | 2 +
src/include/storage/pg_shmem.h | 1 +
6 files changed, 120 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index aca8f73a50..6177b819ce 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1582,6 +1582,31 @@ 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 what size of huge pages is used in conjunction 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>
+ Most modern linux systems support <literal>2MB</literal> and <literal>1GB</literal>
+ huge pages, and some architectures supports other sizes as well. For more information
+ on how to check for support and usage, see <xref linkend="linux-huge-pages"/>.
+ </para>
+ <para>
+ Controling huge page size is not supported on Windows.
+ </para>
+ </listitem>
+ </varlistentry>
+
<varlistentry id="guc-temp-buffers" xreflabel="temp_buffers">
<term><varname>temp_buffers</varname> (<type>integer</type>)
<indexterm>
diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml
index 88210c4a5d..cbdbcb4fdf 100644
--- a/doc/src/sgml/runtime.sgml
+++ b/doc/src/sgml/runtime.sgml
@@ -1391,41 +1391,50 @@ 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 pre-allocate
+ huge pages with the the desired huge page 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 supported huge page sizes, using the
+ <filename>/sys</filename> file system. This might look like:
<programlisting>
$ <userinput>head -1 $PGDATA/postmaster.pid</userinput>
4170
$ <userinput>pmap 4170 | awk '/rw-s/ &amp;&amp; /zero/ {print $2}'</userinput>
6490428K
+$ <userinput>ls /sys/kernel/mm/hugepages</userinput>
+hugepages-1048576kB hugepages-2048kB
+</programlisting>
+
+ You can now choose between the supported sizes, 2MiB and 1GiB in this case.
+ By default <productname>PostgreSQL</productname> will use the default huge
+ page size on the system, but that can be configured via
+ <xref linkend="guc-huge-page-size"/>.
+ The default huge page size can be found with:
+<programlisting>
$ <userinput>grep ^Hugepagesize /proc/meminfo</userinput>
Hugepagesize: 2048 kB
</programlisting>
+
+ For <literal>2MiB</literal>,
<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:
<programlisting>
-$ <userinput>sysctl -w vm.nr_hugepages=3170</userinput>
+$ <userinput>echo 3170 | tee /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages</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.
+ also need huge pages. It is also possible to pre allocate huge pages on boot
+ by adding the kernel parameters <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 external fragmentation, so it might be necessary to
+ repeat the command or to reboot. 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>

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 198a6985bf..56419417dc 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -32,6 +32,7 @@
#endif

#include "miscadmin.h"
+#include "port/pg_bitutils.h"
#include "portability/mem.h"
#include "storage/dsm.h"
#include "storage/fd.h"
@@ -466,53 +467,76 @@ PGSharedMemoryAttach(IpcMemoryId shmId,
*
* Returns the (real or assumed) page size into *hugepagesize,
* and the hugepage-related mmap flags to use into *mmap_flags.
- *
- * Currently *mmap_flags is always just MAP_HUGETLB. Someday, on systems
- * that support it, we might OR in additional bits to specify a particular
- * non-default huge page size.
*/
+
+
static void
GetHugePageSize(Size *hugepagesize, int *mmap_flags)
{
- /*
- * If we fail to find out the system's default huge page size, assume it
- * is 2MB. This will work fine when the actual size is less. If it's
- * more, we might get mmap() or munmap() failures due to unaligned
- * requests; but at this writing, there are no reports of any non-Linux
- * systems being picky about that.
- */
- *hugepagesize = 2 * 1024 * 1024;
- *mmap_flags = MAP_HUGETLB;
+ if (huge_page_size != 0)
+ {
+ /* If huge page size is provided in in config we use that size */
+ *hugepagesize = (Size) huge_page_size * 1024;
+ }
+ else
+ {
+ /*
+ * If we fail to find out the system's default huge page size, or no
+ * huge page size is provided in config, assume it is 2MB. This will
+ * work fine when the actual size is less. If it's more, we might get
+ * mmap() or munmap() failures due to unaligned requests; but at this
+ * writing, there are no reports of any non-Linux systems being picky
+ * about that.
+ */
+ *hugepagesize = 2 * 1024 * 1024;

- /*
- * System-dependent code to find out the default huge page size.
- *
- * On Linux, read /proc/meminfo looking for a line like "Hugepagesize:
- * nnnn kB". Ignore any failures, falling back to the preset default.
- */
+ /*
+ * System-dependent code to find out the default huge page size.
+ *
+ * On Linux, read /proc/meminfo looking for a line like "Hugepagesize:
+ * nnnn kB". Ignore any failures, falling back to the preset default.
+ */
#ifdef __linux__
- {
- FILE *fp = AllocateFile("/proc/meminfo", "r");
- char buf[128];
- unsigned int sz;
- char ch;

- if (fp)
{
- while (fgets(buf, sizeof(buf), fp))
+ FILE *fp = AllocateFile("/proc/meminfo", "r");
+ char buf[128];
+ unsigned int sz;
+ char ch;
+
+ if (fp)
{
- if (sscanf(buf, "Hugepagesize: %u %c", &sz, &ch) == 2)
+ while (fgets(buf, sizeof(buf), fp))
{
- if (ch == 'k')
+ if (sscanf(buf, "Hugepagesize: %u %c", &sz, &ch) == 2)
{
- *hugepagesize = sz * (Size) 1024;
- break;
+ if (ch == 'k')
+ {
+ *hugepagesize = sz * (Size) 1024;
+ break;
+ }
+ /* We could accept other units besides kB, if needed */
}
- /* We could accept other units besides kB, if needed */
}
+ FreeFile(fp);
}
- FreeFile(fp);
}
+#endif /* __linux__ */
+ }
+
+ *mmap_flags = MAP_HUGETLB;
+
+ /*
+ * System-dependent code to configure mmap_flags.
+ *
+ * On Linux, configure flags to include page size, since default huge page
+ * size will be used in case no size is provided.
+ */
+#ifdef __linux__
+ {
+ int shift = pg_ceil_log2_64(*hugepagesize);
+
+ *mmap_flags |= (shift & MAP_HUGE_MASK) << MAP_HUGE_SHIFT;
}
#endif /* __linux__ */
}
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 2f3e0a70e0..b482c660cf 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -585,6 +585,7 @@ int ssl_renegotiation_limit;
* need to be duplicated in all the different implementations of pg_shmem.c.
*/
int huge_pages;
+int huge_page_size;

/*
* These variables are all dummies that don't do anything, except in some
@@ -2269,6 +2270,16 @@ static struct config_int ConfigureNamesInt[] =
1024, 16, INT_MAX / 2,
NULL, NULL, NULL
},
+ {
+ {"huge_page_size", PGC_POSTMASTER, RESOURCES_MEM,
+ gettext_noop("The size of huge page that should be used."),
+ NULL,
+ GUC_UNIT_KB
+ },
+ &huge_page_size,
+ 0, 0, INT_MAX,
+ NULL, NULL, NULL
+ },

{
{"temp_buffers", PGC_USERSET, RESOURCES_MEM,
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index ac02bd0c00..750d3f6245 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -122,6 +122,8 @@
# (change requires restart)
#huge_pages = try # on, off, or try
# (change requires restart)
+#huge_page_size = 0 # use defualt huge page size when set to zero
+ # (change requires restart)
#temp_buffers = 8MB # min 800kB
#max_prepared_transactions = 0 # zero disables the feature
# (change requires restart)
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 0de26b3427..9992932a00 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -44,6 +44,7 @@ typedef struct PGShmemHeader /* standard header for all Postgres shmem */
/* GUC variables */
extern int shared_memory_type;
extern int huge_pages;
+extern int huge_page_size;

/* Possible values for huge_pages */
typedef enum
--
2.27.0