From 0bbafb534275686e780aae2964382e56321c61af Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Mon, 9 Oct 2023 11:23:50 +0300
Subject: [PATCH] Allocate Backend structs in PostmasterContext.

The child processes don't need them. By allocating them in
PostmasterContext, the memory gets free'd and is made available for
other stuff in the child processes.

Reviewed-by: Thomas Munro
Discussion: https://www.postgresql.org/message-id/4f95c1fc-ad3c-7974-3a8c-6faa3931804c@iki.fi
---
 src/backend/postmaster/bgworker.c   | 11 ++++++++---
 src/backend/postmaster/postmaster.c | 24 +++++++++++-------------
 2 files changed, 19 insertions(+), 16 deletions(-)

diff --git a/src/backend/postmaster/bgworker.c b/src/backend/postmaster/bgworker.c
index 31350d6401..cc66c61dee 100644
--- a/src/backend/postmaster/bgworker.c
+++ b/src/backend/postmaster/bgworker.c
@@ -33,6 +33,7 @@
 #include "storage/shmem.h"
 #include "tcop/tcopprot.h"
 #include "utils/ascii.h"
+#include "utils/memutils.h"
 #include "utils/ps_status.h"
 #include "utils/timeout.h"
 
@@ -347,7 +348,9 @@ BackgroundWorkerStateChange(bool allow_new_workers)
 		/*
 		 * Copy the registration data into the registered workers list.
 		 */
-		rw = malloc(sizeof(RegisteredBgWorker));
+		rw = MemoryContextAllocExtended(PostmasterContext,
+										sizeof(RegisteredBgWorker),
+										MCXT_ALLOC_NO_OOM);
 		if (rw == NULL)
 		{
 			ereport(LOG,
@@ -455,7 +458,7 @@ ForgetBackgroundWorker(slist_mutable_iter *cur)
 							 rw->rw_worker.bgw_name)));
 
 	slist_delete_current(cur);
-	free(rw);
+	pfree(rw);
 }
 
 /*
@@ -951,7 +954,9 @@ RegisterBackgroundWorker(BackgroundWorker *worker)
 	/*
 	 * Copy the registration data into the registered workers list.
 	 */
-	rw = malloc(sizeof(RegisteredBgWorker));
+	rw = MemoryContextAllocExtended(PostmasterContext,
+									sizeof(RegisteredBgWorker),
+									MCXT_ALLOC_NO_OOM);
 	if (rw == NULL)
 	{
 		ereport(LOG,
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index bc3c992a3a..583c9b0324 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -3321,7 +3321,7 @@ CleanupBackgroundWorker(int pid,
 		 */
 		if (rw->rw_backend->bgworker_notify)
 			BackgroundWorkerStopNotifications(rw->rw_pid);
-		free(rw->rw_backend);
+		pfree(rw->rw_backend);
 		rw->rw_backend = NULL;
 		rw->rw_pid = 0;
 		rw->rw_child_slot = 0;
@@ -3414,7 +3414,7 @@ CleanupBackend(int pid,
 				BackgroundWorkerStopNotifications(bp->pid);
 			}
 			dlist_delete(iter.cur);
-			free(bp);
+			pfree(bp);
 			break;
 		}
 	}
@@ -3470,7 +3470,7 @@ HandleChildCrash(int pid, int exitstatus, const char *procname)
 #ifdef EXEC_BACKEND
 			ShmemBackendArrayRemove(rw->rw_backend);
 #endif
-			free(rw->rw_backend);
+			pfree(rw->rw_backend);
 			rw->rw_backend = NULL;
 			rw->rw_pid = 0;
 			rw->rw_child_slot = 0;
@@ -3507,7 +3507,7 @@ HandleChildCrash(int pid, int exitstatus, const char *procname)
 #endif
 			}
 			dlist_delete(iter.cur);
-			free(bp);
+			pfree(bp);
 			/* Keep looping so we can signal remaining backends */
 		}
 		else
@@ -4083,7 +4083,7 @@ BackendStartup(Port *port)
 	 * Create backend data structure.  Better before the fork() so we can
 	 * handle failure cleanly.
 	 */
-	bn = (Backend *) malloc(sizeof(Backend));
+	bn = (Backend *) palloc_extended(sizeof(Backend), MCXT_ALLOC_NO_OOM);
 	if (!bn)
 	{
 		ereport(LOG,
@@ -4099,7 +4099,7 @@ BackendStartup(Port *port)
 	 */
 	if (!RandomCancelKey(&MyCancelKey))
 	{
-		free(bn);
+		pfree(bn);
 		ereport(LOG,
 				(errcode(ERRCODE_INTERNAL_ERROR),
 				 errmsg("could not generate random cancel key")));
@@ -4129,8 +4129,6 @@ BackendStartup(Port *port)
 	pid = fork_process();
 	if (pid == 0)				/* child */
 	{
-		free(bn);
-
 		/* Detangle from postmaster */
 		InitPostmasterChild();
 
@@ -4161,7 +4159,7 @@ BackendStartup(Port *port)
 
 		if (!bn->dead_end)
 			(void) ReleasePostmasterChildSlot(bn->child_slot);
-		free(bn);
+		pfree(bn);
 		errno = save_errno;
 		ereport(LOG,
 				(errmsg("could not fork new process for connection: %m")));
@@ -5424,7 +5422,7 @@ StartAutovacuumWorker(void)
 			return;
 		}
 
-		bn = (Backend *) malloc(sizeof(Backend));
+		bn = (Backend *) palloc_extended(sizeof(Backend), MCXT_ALLOC_NO_OOM);
 		if (bn)
 		{
 			bn->cancel_key = MyCancelKey;
@@ -5451,7 +5449,7 @@ StartAutovacuumWorker(void)
 			 * logged by StartAutoVacWorker
 			 */
 			(void) ReleasePostmasterChildSlot(bn->child_slot);
-			free(bn);
+			pfree(bn);
 		}
 		else
 			ereport(LOG,
@@ -5696,7 +5694,7 @@ do_start_bgworker(RegisteredBgWorker *rw)
 			/* undo what assign_backendlist_entry did */
 			ReleasePostmasterChildSlot(rw->rw_child_slot);
 			rw->rw_child_slot = 0;
-			free(rw->rw_backend);
+			pfree(rw->rw_backend);
 			rw->rw_backend = NULL;
 			/* mark entry as crashed, so we'll try again later */
 			rw->rw_crashed_at = GetCurrentTimestamp();
@@ -5822,7 +5820,7 @@ assign_backendlist_entry(RegisteredBgWorker *rw)
 		return false;
 	}
 
-	bn = malloc(sizeof(Backend));
+	bn = palloc_extended(sizeof(Backend), MCXT_ALLOC_NO_OOM);
 	if (bn == NULL)
 	{
 		ereport(LOG,