v3-0002-Replace-ShmemAlloc-calls-by-ShmemInitStruct.patch

From 598287c0d366bc32def8e39a747f8f4418376706 Mon Sep 17 00:00:00 2001
From: Rahila Syed <rahilasyed.90@gmail.com>
Date: Thu, 6 Mar 2025 20:32:27 +0530
Subject: [PATCH 2/2] Replace ShmemAlloc calls by ShmemInitStruct

The shared memory allocated by ShmemAlloc is not tracked
by pg_shmem_allocations. This commit replaces most of the
calls to ShmemAlloc by ShmemInitStruct to associate a name
with the allocations and ensure that they get tracked by
pg_shmem_allocations. It also merges several smaller
ShmemAlloc calls into larger ShmemInitStruct to allocate
and track all the related memory allocations under single
---
 src/backend/storage/lmgr/predicate.c | 17 +++++++-------
 src/backend/storage/lmgr/proc.c      | 33 +++++++++++++++++++++++-----
 2 files changed, 36 insertions(+), 14 deletions(-)

diff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.c
index 5b21a05398..dd66990335 100644
--- a/src/backend/storage/lmgr/predicate.c
+++ b/src/backend/storage/lmgr/predicate.c
@@ -1226,8 +1226,11 @@ PredicateLockShmemInit(void)
 	 */
 	max_table_size *= 10;
 
+	requestSize = add_size(PredXactListDataSize,
+						   (mul_size((Size) max_table_size,
+									 sizeof(SERIALIZABLEXACT))));
 	PredXact = ShmemInitStruct("PredXactList",
-							   PredXactListDataSize,
+							   requestSize,
 							   &found);
 	Assert(found == IsUnderPostmaster);
 	if (!found)
@@ -1242,9 +1245,7 @@ PredicateLockShmemInit(void)
 		PredXact->LastSxactCommitSeqNo = FirstNormalSerCommitSeqNo - 1;
 		PredXact->CanPartialClearThrough = 0;
 		PredXact->HavePartialClearedThrough = 0;
-		requestSize = mul_size((Size) max_table_size,
-							   sizeof(SERIALIZABLEXACT));
-		PredXact->element = ShmemAlloc(requestSize);
+		PredXact->element = (SERIALIZABLEXACT *) ((char *) PredXact + PredXactListDataSize);
 		/* Add all elements to available list, clean. */
 		memset(PredXact->element, 0, requestSize);
 		for (i = 0; i < max_table_size; i++)
@@ -1299,9 +1300,11 @@ PredicateLockShmemInit(void)
 	 * probably OK.
 	 */
 	max_table_size *= 5;
+	requestSize = mul_size((Size) max_table_size,
+						   RWConflictDataSize);
 
 	RWConflictPool = ShmemInitStruct("RWConflictPool",
-									 RWConflictPoolHeaderDataSize,
+									 RWConflictPoolHeaderDataSize + requestSize,
 									 &found);
 	Assert(found == IsUnderPostmaster);
 	if (!found)
@@ -1309,9 +1312,7 @@ PredicateLockShmemInit(void)
 		int			i;
 
 		dlist_init(&RWConflictPool->availableList);
-		requestSize = mul_size((Size) max_table_size,
-							   RWConflictDataSize);
-		RWConflictPool->element = ShmemAlloc(requestSize);
+		RWConflictPool->element = (RWConflict) ((char *) RWConflictPool + RWConflictPoolHeaderDataSize);
 		/* Add all elements to available list, clean. */
 		memset(RWConflictPool->element, 0, requestSize);
 		for (i = 0; i < max_table_size; i++)
diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index 749a79d48e..3ae817dedc 100644
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -88,6 +88,7 @@ static void RemoveProcFromArray(int code, Datum arg);
 static void ProcKill(int code, Datum arg);
 static void AuxiliaryProcKill(int code, Datum arg);
 static void CheckDeadLock(void);
+static Size PGProcShmemSize(void);
 
 
 /*
@@ -175,6 +176,7 @@ InitProcGlobal(void)
 			   *fpEndPtr PG_USED_FOR_ASSERTS_ONLY;
 	Size		fpLockBitsSize,
 				fpRelIdSize;
+	Size		requestSize;
 
 	/* Create the ProcGlobal shared structure */
 	ProcGlobal = (PROC_HDR *)
@@ -204,7 +206,10 @@ InitProcGlobal(void)
 	 * with a single freelist.)  Each PGPROC structure is dedicated to exactly
 	 * one of these purposes, and they do not move between groups.
 	 */
-	procs = (PGPROC *) ShmemAlloc(TotalProcs * sizeof(PGPROC));
+	requestSize = PGProcShmemSize();
+
+	procs = (PGPROC *) ShmemInitStruct("PGPROC structures", requestSize, &found);
+
 	MemSet(procs, 0, TotalProcs * sizeof(PGPROC));
 	ProcGlobal->allProcs = procs;
 	/* XXX allProcCount isn't really all of them; it excludes prepared xacts */
@@ -218,11 +223,11 @@ InitProcGlobal(void)
 	 * how hotly they are accessed.
 	 */
 	ProcGlobal->xids =
-		(TransactionId *) ShmemAlloc(TotalProcs * sizeof(*ProcGlobal->xids));
+		(TransactionId *) ((char *) procs + TotalProcs * sizeof(PGPROC));
 	MemSet(ProcGlobal->xids, 0, TotalProcs * sizeof(*ProcGlobal->xids));
-	ProcGlobal->subxidStates = (XidCacheStatus *) ShmemAlloc(TotalProcs * sizeof(*ProcGlobal->subxidStates));
+	ProcGlobal->subxidStates = (XidCacheStatus *) ((char *) ProcGlobal->xids + TotalProcs * sizeof(*ProcGlobal->xids) + PG_CACHE_LINE_SIZE);
 	MemSet(ProcGlobal->subxidStates, 0, TotalProcs * sizeof(*ProcGlobal->subxidStates));
-	ProcGlobal->statusFlags = (uint8 *) ShmemAlloc(TotalProcs * sizeof(*ProcGlobal->statusFlags));
+	ProcGlobal->statusFlags = (uint8 *) ((char *) ProcGlobal->subxidStates + TotalProcs * sizeof(*ProcGlobal->subxidStates) + PG_CACHE_LINE_SIZE);
 	MemSet(ProcGlobal->statusFlags, 0, TotalProcs * sizeof(*ProcGlobal->statusFlags));
 
 	/*
@@ -233,7 +238,7 @@ InitProcGlobal(void)
 	fpLockBitsSize = MAXALIGN(FastPathLockGroupsPerBackend * sizeof(uint64));
 	fpRelIdSize = MAXALIGN(FastPathLockSlotsPerBackend() * sizeof(Oid));
 
-	fpPtr = ShmemAlloc(TotalProcs * (fpLockBitsSize + fpRelIdSize));
+	fpPtr = ShmemInitStruct("Fast path lock arrays", TotalProcs * (fpLockBitsSize + fpRelIdSize), &found);
 	MemSet(fpPtr, 0, TotalProcs * (fpLockBitsSize + fpRelIdSize));
 
 	/* For asserts checking we did not overflow. */
@@ -330,10 +335,26 @@ InitProcGlobal(void)
 	PreparedXactProcs = &procs[MaxBackends + NUM_AUXILIARY_PROCS];
 
 	/* Create ProcStructLock spinlock, too */
-	ProcStructLock = (slock_t *) ShmemAlloc(sizeof(slock_t));
+	ProcStructLock = (slock_t *) ShmemInitStruct("ProcStructLock spinlock", sizeof(slock_t), &found);
 	SpinLockInit(ProcStructLock);
 }
 
+static Size
+PGProcShmemSize(void)
+{
+	Size		size;
+	uint32		TotalProcs = MaxBackends + NUM_AUXILIARY_PROCS + max_prepared_xacts;
+
+	size = TotalProcs * sizeof(PGPROC);
+	size = add_size(size, TotalProcs * sizeof(*ProcGlobal->xids));
+	size = add_size(size, PG_CACHE_LINE_SIZE);
+	size = add_size(size, TotalProcs * sizeof(*ProcGlobal->subxidStates));
+	size = add_size(size, PG_CACHE_LINE_SIZE);
+	size = add_size(size, TotalProcs * sizeof(*ProcGlobal->statusFlags));
+	size = add_size(size, PG_CACHE_LINE_SIZE);
+	return size;
+}
+
 /*
  * InitProcess -- initialize a per-process PGPROC entry for this backend
  */
-- 
2.34.1