bufmgr: fewer calls to BufferDescriptorGetContentLock

We're planning to merge buffer content locks into BufferDesc.state. To reduce
the size of that patch, centralize calls to BufferDescriptorGetContentLock().

The biggest part of the change is in assertions, by introducing
BufferIsLockedByMe[InMode]() (and removing BufferIsExclusiveLocked()). This
seems like an improvement even without aforementioned plans.

Additionally replace some direct calls to LWLockAcquire() with calls to
LockBuffer().

Reviewed-by: Matthias van de Meent <boekewurm+postgres@gmail.com>
Discussion: https://postgr.es/m/fvfmkr5kk4nyex56ejgxj3uzi63isfxovp2biecb4bspbjrze7@az2pljabhnff

1 files changed, 55 insertions, 15 deletions

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 8ee7d3b441b..da71fcf8d0e 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -1068,7 +1068,7 @@ ZeroAndLockBuffer(Buffer buffer, ReadBufferMode mode, bool already_valid)
 		 * already valid.)
 		 */
 		if (!isLocalBuf)
-			LWLockAcquire(BufferDescriptorGetContentLock(bufHdr), LW_EXCLUSIVE);
+			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
 
 		/* Set BM_VALID, terminate IO, and wake up any waiters */
 		if (isLocalBuf)
@@ -2825,7 +2825,7 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
 		}
 
 		if (lock)
-			LWLockAcquire(BufferDescriptorGetContentLock(buf_hdr), LW_EXCLUSIVE);
+			LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
 
 		TerminateBufferIO(buf_hdr, false, BM_VALID, true, false);
 	}
@@ -2838,14 +2838,40 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
 }
 
 /*
- * BufferIsExclusiveLocked
+ * BufferIsLockedByMe
+ *
+ *      Checks if this backend has the buffer locked in any mode.
+ *
+ * Buffer must be pinned.
+ */
+bool
+BufferIsLockedByMe(Buffer buffer)
+{
+	BufferDesc *bufHdr;
+
+	Assert(BufferIsPinned(buffer));
+
+	if (BufferIsLocal(buffer))
+	{
+		/* Content locks are not maintained for local buffers. */
+		return true;
+	}
+	else
+	{
+		bufHdr = GetBufferDescriptor(buffer - 1);
+		return LWLockHeldByMe(BufferDescriptorGetContentLock(bufHdr));
+	}
+}
+
+/*
+ * BufferIsLockedByMeInMode
  *
- *      Checks if buffer is exclusive-locked.
+ *      Checks if this backend has the buffer locked in the specified mode.
  *
  * Buffer must be pinned.
  */
 bool
-BufferIsExclusiveLocked(Buffer buffer)
+BufferIsLockedByMeInMode(Buffer buffer, int mode)
 {
 	BufferDesc *bufHdr;
 
@@ -2858,9 +2884,23 @@ BufferIsExclusiveLocked(Buffer buffer)
 	}
 	else
 	{
+		LWLockMode	lw_mode;
+
+		switch (mode)
+		{
+			case BUFFER_LOCK_EXCLUSIVE:
+				lw_mode = LW_EXCLUSIVE;
+				break;
+			case BUFFER_LOCK_SHARE:
+				lw_mode = LW_SHARED;
+				break;
+			default:
+				pg_unreachable();
+		}
+
 		bufHdr = GetBufferDescriptor(buffer - 1);
 		return LWLockHeldByMeInMode(BufferDescriptorGetContentLock(bufHdr),
-									LW_EXCLUSIVE);
+									lw_mode);
 	}
 }
 
@@ -2889,8 +2929,7 @@ BufferIsDirty(Buffer buffer)
 	else
 	{
 		bufHdr = GetBufferDescriptor(buffer - 1);
-		Assert(LWLockHeldByMeInMode(BufferDescriptorGetContentLock(bufHdr),
-									LW_EXCLUSIVE));
+		Assert(BufferIsLockedByMeInMode(buffer, BUFFER_LOCK_EXCLUSIVE));
 	}
 
 	return pg_atomic_read_u32(&bufHdr->state) & BM_DIRTY;
@@ -2924,8 +2963,7 @@ MarkBufferDirty(Buffer buffer)
 	bufHdr = GetBufferDescriptor(buffer - 1);
 
 	Assert(BufferIsPinned(buffer));
-	Assert(LWLockHeldByMeInMode(BufferDescriptorGetContentLock(bufHdr),
-								LW_EXCLUSIVE));
+	Assert(BufferIsLockedByMeInMode(buffer, BUFFER_LOCK_EXCLUSIVE));
 
 	old_buf_state = pg_atomic_read_u32(&bufHdr->state);
 	for (;;)
@@ -3259,7 +3297,10 @@ UnpinBufferNoOwner(BufferDesc *buf)
 		 */
 		VALGRIND_MAKE_MEM_NOACCESS(BufHdrGetBlock(buf), BLCKSZ);
 
-		/* I'd better not still hold the buffer content lock */
+		/*
+		 * I'd better not still hold the buffer content lock. Can't use
+		 * BufferIsLockedByMe(), as that asserts the buffer is pinned.
+		 */
 		Assert(!LWLockHeldByMe(BufferDescriptorGetContentLock(buf)));
 
 		/*
@@ -5324,7 +5365,7 @@ FlushOneBuffer(Buffer buffer)
 
 	bufHdr = GetBufferDescriptor(buffer - 1);
 
-	Assert(LWLockHeldByMe(BufferDescriptorGetContentLock(bufHdr)));
+	Assert(BufferIsLockedByMe(buffer));
 
 	FlushBuffer(bufHdr, NULL, IOOBJECT_RELATION, IOCONTEXT_NORMAL);
 }
@@ -5415,7 +5456,7 @@ MarkBufferDirtyHint(Buffer buffer, bool buffer_std)
 
 	Assert(GetPrivateRefCount(buffer) > 0);
 	/* here, either share or exclusive lock is OK */
-	Assert(LWLockHeldByMe(BufferDescriptorGetContentLock(bufHdr)));
+	Assert(BufferIsLockedByMe(buffer));
 
 	/*
 	 * This routine might get called many times on the same page, if we are
@@ -5898,8 +5939,7 @@ IsBufferCleanupOK(Buffer buffer)
 	bufHdr = GetBufferDescriptor(buffer - 1);
 
 	/* caller must hold exclusive lock on buffer */
-	Assert(LWLockHeldByMeInMode(BufferDescriptorGetContentLock(bufHdr),
-								LW_EXCLUSIVE));
+	Assert(BufferIsLockedByMeInMode(buffer, BUFFER_LOCK_EXCLUSIVE));
 
 	buf_state = LockBufHdr(bufHdr);