Hi, On 26/02/14 13:13, Alvaro Herrera wrote: > > There's one thing that rubs me the wrong way about all this > functionality, which is that we've named it "huge TLB pages". That is > wrong -- the TLB pages are not huge. In fact, as far as I understand, > the TLB doesn't have pages at all. It's the pages that are huge, but > those pages are not TLB pages, they are just memory pages.
I didn't think about this, yet, but you are totally right. > Since we haven't released any of this, should we discuss renaming it to > just "huge pages"? Attached is a patch with the updated documentation (now uses consistently huge pages) as well as a renamed GUC, consistent wording (always use huge pages) as well as renamed variables. Should I create a new commit fest entry for this and delete the old one? Or should this be done in two patches? Locally in my repo this is done with two commits, so it would be easy to split that. Best regards, -- Christian Kruse http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index cf11306..77c778f 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1166,35 +1166,33 @@ 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 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>.
+ <productname>PostgreSQL</productname> will
+ refuse to start when set to <literal>on</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 bbb808f..7f4a235 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>
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 65ad595..51c1a2b 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -333,12 +333,12 @@ CreateAnonymousSegment(Size *size)
int mmap_errno = 0;
#ifndef MAP_HUGETLB
- if (huge_tlb_pages == HUGE_TLB_ON)
+ if (huge_pages == HUGE_PAGES_ON)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("huge TLB pages not supported on this platform")));
#else
- if (huge_tlb_pages == HUGE_TLB_ON || huge_tlb_pages == HUGE_TLB_TRY)
+ if (huge_pages == HUGE_PAGES_ON || huge_pages == HUGE_PAGES_TRY)
{
/*
* Round up the request size to a suitable large value.
@@ -364,13 +364,13 @@ CreateAnonymousSegment(Size *size)
ptr = mmap(NULL, allocsize, PROT_READ | PROT_WRITE,
PG_MMAP_FLAGS | MAP_HUGETLB, -1, 0);
mmap_errno = errno;
- if (huge_tlb_pages == HUGE_TLB_TRY && ptr == MAP_FAILED)
+ if (huge_pages == HUGE_PAGES_TRY && ptr == MAP_FAILED)
elog(DEBUG1, "mmap with MAP_HUGETLB failed, huge pages disabled: %m");
}
#endif
- if (huge_tlb_pages == HUGE_TLB_OFF ||
- (huge_tlb_pages == HUGE_TLB_TRY && ptr == MAP_FAILED))
+ if (huge_pages == HUGE_PAGES_OFF ||
+ (huge_pages == HUGE_PAGES_TRY && ptr == MAP_FAILED))
{
/*
* use the original size, not the rounded up value, when falling
@@ -431,10 +431,10 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port)
Size sysvsize;
#if defined(EXEC_BACKEND) || !defined(MAP_HUGETLB)
- if (huge_tlb_pages == HUGE_TLB_ON)
+ if (huge_pages == HUGE_PAGES_ON)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
- errmsg("huge TLB pages not supported on this platform")));
+ errmsg("huge pages not supported on this platform")));
#endif
/* Room for a header? */
diff --git a/src/backend/port/win32_shmem.c b/src/backend/port/win32_shmem.c
index 9b0cceb..dca371c 100644
--- a/src/backend/port/win32_shmem.c
+++ b/src/backend/port/win32_shmem.c
@@ -128,10 +128,10 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port)
DWORD size_high;
DWORD size_low;
- if (huge_tlb_pages == HUGE_TLB_ON)
+ if (huge_pages == HUGE_PAGES_ON)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
- errmsg("huge TLB pages not supported on this platform")));
+ errmsg("huge pages not supported on this platform")));
/* Room for a header? */
Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index b27cb89..c76edb4 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -393,16 +393,16 @@ static const struct config_enum_entry synchronous_commit_options[] = {
* Although only "on", "off", "try" are documented, we accept all the likely
* variants of "on" and "off".
*/
-static const struct config_enum_entry huge_tlb_options[] = {
- {"off", HUGE_TLB_OFF, false},
- {"on", HUGE_TLB_ON, false},
- {"try", HUGE_TLB_TRY, false},
- {"true", HUGE_TLB_ON, true},
- {"false", HUGE_TLB_OFF, true},
- {"yes", HUGE_TLB_ON, true},
- {"no", HUGE_TLB_OFF, true},
- {"1", HUGE_TLB_ON, true},
- {"0", HUGE_TLB_OFF, true},
+static const struct config_enum_entry huge_pages_options[] = {
+ {"off", HUGE_PAGES_OFF, false},
+ {"on", HUGE_PAGES_ON, false},
+ {"try", HUGE_PAGES_TRY, false},
+ {"true", HUGE_PAGES_ON, true},
+ {"false", HUGE_PAGES_OFF, true},
+ {"yes", HUGE_PAGES_ON, true},
+ {"no", HUGE_PAGES_OFF, true},
+ {"1", HUGE_PAGES_ON, true},
+ {"0", HUGE_PAGES_OFF, true},
{NULL, 0, false}
};
@@ -470,7 +470,7 @@ int tcp_keepalives_count;
* This really belongs in pg_shmem.c, but is defined here so that it doesn't
* need to be duplicated in all the different implementations of pg_shmem.c.
*/
-int huge_tlb_pages;
+int huge_pages;
/*
* These variables are all dummies that don't do anything, except in some
@@ -3497,12 +3497,12 @@ static struct config_enum ConfigureNamesEnum[] =
},
{
- {"huge_tlb_pages", PGC_POSTMASTER, RESOURCES_MEM,
- gettext_noop("Use of huge TLB pages on Linux"),
+ {"huge_pages", PGC_POSTMASTER, RESOURCES_MEM,
+ gettext_noop("Use of huge pages on Linux"),
NULL
},
- &huge_tlb_pages,
- HUGE_TLB_TRY, huge_tlb_options,
+ &huge_pages,
+ HUGE_PAGES_TRY, huge_pages_options,
NULL, NULL, NULL
},
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index ce56059..3629a52 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -115,7 +115,7 @@
#shared_buffers = 32MB # min 128kB
# (change requires restart)
-#huge_tlb_pages = try # on, off, or try
+#huge_pages = try # on, off, or try
# (change requires restart)
#temp_buffers = 8MB # min 800kB
#max_prepared_transactions = 0 # zero disables the feature
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 0d60729..0dc960b 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -39,15 +39,15 @@ typedef struct PGShmemHeader /* standard header for all Postgres shmem */
} PGShmemHeader;
/* GUC variable */
-extern int huge_tlb_pages;
+extern int huge_pages;
-/* Possible values for huge_tlb_pages */
+/* Possible values for huge_pages */
typedef enum
{
- HUGE_TLB_OFF,
- HUGE_TLB_ON,
- HUGE_TLB_TRY
-} HugeTlbType;
+ HUGE_PAGES_OFF,
+ HUGE_PAGES_ON,
+ HUGE_PAGES_TRY
+} HugePagesType;
#ifndef WIN32
extern unsigned long UsedShmemSegID;
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