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Support Linux's oom_score_adj API as well as the older oom_adj API.

The simplest way to handle this is just to copy-and-paste the relevant
code block in fork_process.c, so that's what I did. (It's possible that
something more complicated would be useful to packagers who want to work
with either the old or the new API; but at this point the number of such
people is rapidly approaching zero, so let's just get the minimal thing
done.)  Update relevant documentation as well.
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1 parent b9212e3 commit 93f4d7f806613d28842f956a84f31cc41d825503 @tglsfdc tglsfdc committed Jun 13, 2012
Showing with 59 additions and 16 deletions.
  1. +10 −4 contrib/start-scripts/linux
  2. +16 −7 doc/src/sgml/runtime.sgml
  3. +33 −5 src/backend/postmaster/fork_process.c
@@ -42,10 +42,14 @@ PGLOG="$PGDATA/serverlog"
# It's often a good idea to protect the postmaster from being killed by the
# OOM killer (which will tend to preferentially kill the postmaster because
-# of the way it accounts for shared memory). Setting the OOM_ADJ value to
-# -17 will disable OOM kill altogether. If you enable this, you probably want
-# to compile PostgreSQL with "-DLINUX_OOM_ADJ=0", so that individual backends
-# can still be killed by the OOM killer.
+# of the way it accounts for shared memory). Setting the OOM_SCORE_ADJ value
+# to -1000 will disable OOM kill altogether. If you enable this, you probably
+# want to compile PostgreSQL with "-DLINUX_OOM_SCORE_ADJ=0", so that
+# individual backends can still be killed by the OOM killer.
+#OOM_SCORE_ADJ=-1000
+# Older Linux kernels may not have /proc/self/oom_score_adj, but instead
+# /proc/self/oom_adj, which works similarly except the disable value is -17.
+# For such a system, enable this and compile with "-DLINUX_OOM_ADJ=0".
#OOM_ADJ=-17
## STOP EDITING HERE
@@ -78,6 +82,7 @@ test -x $DAEMON ||
case $1 in
start)
echo -n "Starting PostgreSQL: "
+ test x"$OOM_SCORE_ADJ" != x && echo "$OOM_SCORE_ADJ" > /proc/self/oom_score_adj
test x"$OOM_ADJ" != x && echo "$OOM_ADJ" > /proc/self/oom_adj
su - $PGUSER -c "$DAEMON -D '$PGDATA' &" >>$PGLOG 2>&1
echo "ok"
@@ -90,6 +95,7 @@ case $1 in
restart)
echo -n "Restarting PostgreSQL: "
su - $PGUSER -c "$PGCTL stop -D '$PGDATA' -s -m fast -w"
+ test x"$OOM_SCORE_ADJ" != x && echo "$OOM_SCORE_ADJ" > /proc/self/oom_score_adj
test x"$OOM_ADJ" != x && echo "$OOM_ADJ" > /proc/self/oom_adj
su - $PGUSER -c "$DAEMON -D '$PGDATA' &" >>$PGLOG 2>&1
echo "ok"
View
@@ -1268,7 +1268,7 @@ default:\
In Linux 2.4 and later, the default virtual memory behavior is not
optimal for <productname>PostgreSQL</productname>. Because of the
way that the kernel implements memory overcommit, the kernel might
- terminate the <productname>PostgreSQL</productname> server (the
+ terminate the <productname>PostgreSQL</productname> postmaster (the
master server process) if the memory demands of
another process cause the system to run out of virtual memory.
</para>
@@ -1317,22 +1317,31 @@ sysctl -w vm.overcommit_memory=2
<para>
Another approach, which can be used with or without altering
<varname>vm.overcommit_memory</>, is to set the process-specific
- <varname>oom_adj</> value for the postmaster process to <literal>-17</>,
- thereby guaranteeing it will not be targeted by the OOM killer. The
- simplest way to do this is to execute
+ <varname>oom_score_adj</> value for the postmaster process to
+ <literal>-1000</>, thereby guaranteeing it will not be targeted by the OOM
+ killer. The simplest way to do this is to execute
<programlisting>
-echo -17 > /proc/self/oom_adj
+echo -1000 > /proc/self/oom_score_adj
</programlisting>
in the postmaster's startup script just before invoking the postmaster.
Note that this action must be done as root, or it will have no effect;
so a root-owned startup script is the easiest place to do it. If you
do this, you may also wish to build <productname>PostgreSQL</>
- with <literal>-DLINUX_OOM_ADJ=0</> added to <varname>CPPFLAGS</>.
+ with <literal>-DLINUX_OOM_SCORE_ADJ=0</> added to <varname>CPPFLAGS</>.
That will cause postmaster child processes to run with the normal
- <varname>oom_adj</> value of zero, so that the OOM killer can still
+ <varname>oom_score_adj</> value of zero, so that the OOM killer can still
target them at need.
</para>
+ <para>
+ Older Linux kernels do not offer <filename>/proc/self/oom_score_adj</>,
+ but may have a previous version of the same functionality called
+ <filename>/proc/self/oom_adj</>. This works the same except the disable
+ value is <literal>-17</> not <literal>-1000</>. The corresponding
+ build flag for <productname>PostgreSQL</> is
+ <literal>-DLINUX_OOM_ADJ=0</>.
+ </para>
+
<note>
<para>
Some vendors' Linux 2.4 kernels are reported to have early versions
@@ -68,12 +68,40 @@ fork_process(void)
* process sizes *including shared memory*. (This is unbelievably
* stupid, but the kernel hackers seem uninterested in improving it.)
* Therefore it's often a good idea to protect the postmaster by
- * setting its oom_adj value negative (which has to be done in a
- * root-owned startup script). If you just do that much, all child
+ * setting its oom_score_adj value negative (which has to be done in a
+ * root-owned startup script). If you just do that much, all child
* processes will also be protected against OOM kill, which might not
- * be desirable. You can then choose to build with LINUX_OOM_ADJ
- * #defined to 0, or some other value that you want child processes to
- * adopt here.
+ * be desirable. You can then choose to build with
+ * LINUX_OOM_SCORE_ADJ #defined to 0, or to some other value that you
+ * want child processes to adopt here.
+ */
+#ifdef LINUX_OOM_SCORE_ADJ
+ {
+ /*
+ * Use open() not stdio, to ensure we control the open flags. Some
+ * Linux security environments reject anything but O_WRONLY.
+ */
+ int fd = open("/proc/self/oom_score_adj", O_WRONLY, 0);
+
+ /* We ignore all errors */
+ if (fd >= 0)
+ {
+ char buf[16];
+ int rc;
+
+ snprintf(buf, sizeof(buf), "%d\n", LINUX_OOM_SCORE_ADJ);
+ rc = write(fd, buf, strlen(buf));
+ (void) rc;
+ close(fd);
+ }
+ }
+#endif /* LINUX_OOM_SCORE_ADJ */
+
+ /*
+ * Older Linux kernels have oom_adj not oom_score_adj. This works
+ * similarly except with a different scale of adjustment values.
+ * If it's necessary to build Postgres to work with either API,
+ * you can define both LINUX_OOM_SCORE_ADJ and LINUX_OOM_ADJ.
*/
#ifdef LINUX_OOM_ADJ
{

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