Improve our mechanism for controlling the Linux out-of-memory killer.

Arrange for postmaster child processes to respond to two environment
variables, PG_OOM_ADJUST_FILE and PG_OOM_ADJUST_VALUE, to determine whether
they reset their OOM score adjustments and if so to what.  This is superior
to the previous design involving #ifdef's in several ways.  The behavior is
now available in a default build, and both ends of the adjustment --- the
original adjustment of the postmaster's level and the subsequent
readjustment by child processes --- can now be controlled in one place,
namely the postmaster launch script.  So it's no longer necessary for the
launch script to act on faith that the server was compiled with the
appropriate options.  In addition, if someone wants to use an OOM score
other than zero for the child processes, that doesn't take a recompile
anymore; and we no longer have to cater separately to the two different
historical kernel APIs for this adjustment.

Gurjeet Singh, somewhat revised by me

1 files changed, 9 insertions, 6 deletions

diff --git a/contrib/start-scripts/linux b/contrib/start-scripts/linux
index b950cf512c3..bab8b0efc67 100644
--- a/contrib/start-scripts/linux
+++ b/contrib/start-scripts/linux
@@ -43,14 +43,17 @@ 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_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.
+# to -1000 will disable OOM kill altogether, which is a good thing for the
+# postmaster, but not so much for individual backends.  If you enable this,
+# also uncomment the DAEMON_ENV line, which will instruct backends to set
+# their OOM adjustments back to the default setting of zero.
 #OOM_SCORE_ADJ=-1000
+#DAEMON_ENV="PG_OOM_ADJUST_FILE=/proc/self/oom_score_adj"
 # 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".
+# For such a system, uncomment these two lines instead.
 #OOM_ADJ=-17
+#DAEMON_ENV="PG_OOM_ADJUST_FILE=/proc/self/oom_adj"
 
 ## STOP EDITING HERE
 
@@ -84,7 +87,7 @@ case $1 in
 	echo -n "Starting PostgreSQL: "
 	test x"$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
+	su - $PGUSER -c "$DAEMON_ENV $DAEMON -D '$PGDATA' &" >>$PGLOG 2>&1
 	echo "ok"
 	;;
   stop)
@@ -97,7 +100,7 @@ case $1 in
 	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
+	su - $PGUSER -c "$DAEMON_ENV $DAEMON -D '$PGDATA' &" >>$PGLOG 2>&1
 	echo "ok"
 	;;
   reload)