bufmgr: Add Pin/UnpinLocalBuffer()

So far these were open-coded in quite a few places, without a good reason.

Reviewed-by: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: David Rowley <dgrowleyml@gmail.com>
Discussion: https://postgr.es/m/20221029025420.eplyow6k7tgu6he3@awork3.anarazel.de

src/backend/storage/buffer/bufmgr.c

@@ -636,20 +636,7 @@ ReadRecentBuffer(RelFileLocator rlocator, ForkNumber forkNum, BlockNumber blockN
 		/* Is it still valid and holding the right tag? */
 		if ((buf_state & BM_VALID) && BufferTagsEqual(&tag, &bufHdr->tag))
 		{
-			/*
-			 * Bump buffer's ref and usage counts. This is equivalent of
-			 * PinBuffer for a shared buffer.
-			 */
-			if (LocalRefCount[b] == 0)
-			{
-				if (BUF_STATE_GET_USAGECOUNT(buf_state) < BM_MAX_USAGE_COUNT)
-				{
-					buf_state += BUF_USAGECOUNT_ONE;
-					pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);
-				}
-			}
-			LocalRefCount[b]++;
-			ResourceOwnerRememberBuffer(CurrentResourceOwner, recent_buffer);
+			PinLocalBuffer(bufHdr, true);
 
 			pgBufferUsage.local_blks_hit++;
 
@@ -1688,8 +1675,7 @@ ReleaseAndReadBuffer(Buffer buffer,
 				BufTagMatchesRelFileLocator(&bufHdr->tag, &relation->rd_locator) &&
 				BufTagGetForkNum(&bufHdr->tag) == forkNum)
 				return buffer;
-			ResourceOwnerForgetBuffer(CurrentResourceOwner, buffer);
-			LocalRefCount[-buffer - 1]--;
+			UnpinLocalBuffer(buffer);
 		}
 		else
 		{
@@ -3982,15 +3968,9 @@ ReleaseBuffer(Buffer buffer)
 		elog(ERROR, "bad buffer ID: %d", buffer);
 
 	if (BufferIsLocal(buffer))
-	{
-		ResourceOwnerForgetBuffer(CurrentResourceOwner, buffer);
-
-		Assert(LocalRefCount[-buffer - 1] > 0);
-		LocalRefCount[-buffer - 1]--;
-		return;
-	}
-
-	UnpinBuffer(GetBufferDescriptor(buffer - 1));
+		UnpinLocalBuffer(buffer);
+	else
+		UnpinBuffer(GetBufferDescriptor(buffer - 1));
 }
 
 /*

src/backend/storage/buffer/localbuf.c

@@ -137,27 +137,8 @@ LocalBufferAlloc(SMgrRelation smgr, ForkNumber forkNum, BlockNumber blockNum,
 		fprintf(stderr, "LB ALLOC (%u,%d,%d) %d\n",
 				smgr->smgr_rlocator.locator.relNumber, forkNum, blockNum, -b - 1);
 #endif
-		buf_state = pg_atomic_read_u32(&bufHdr->state);
 
-		/* this part is equivalent to PinBuffer for a shared buffer */
-		if (LocalRefCount[b] == 0)
-		{
-			if (BUF_STATE_GET_USAGECOUNT(buf_state) < BM_MAX_USAGE_COUNT)
-			{
-				buf_state += BUF_USAGECOUNT_ONE;
-				pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);
-			}
-		}
-		LocalRefCount[b]++;
-		ResourceOwnerRememberBuffer(CurrentResourceOwner,
-									BufferDescriptorGetBuffer(bufHdr));
-		if (buf_state & BM_VALID)
-			*foundPtr = true;
-		else
-		{
-			/* Previous read attempt must have failed; try again */
-			*foundPtr = false;
-		}
+		*foundPtr = PinLocalBuffer(bufHdr, true);
 		return bufHdr;
 	}
 
@@ -194,9 +175,7 @@ LocalBufferAlloc(SMgrRelation smgr, ForkNumber forkNum, BlockNumber blockNum,
 			else
 			{
 				/* Found a usable buffer */
-				LocalRefCount[b]++;
-				ResourceOwnerRememberBuffer(CurrentResourceOwner,
-											BufferDescriptorGetBuffer(bufHdr));
+				PinLocalBuffer(bufHdr, false);
 				break;
 			}
 		}
@@ -484,6 +463,48 @@ InitLocalBuffers(void)
 	NLocBuffer = nbufs;
 }
 
+/*
+ * XXX: We could have a slightly more efficient version of PinLocalBuffer()
+ * that does not support adjusting the usagecount - but so far it does not
+ * seem worth the trouble.
+ */
+bool
+PinLocalBuffer(BufferDesc *buf_hdr, bool adjust_usagecount)
+{
+	uint32		buf_state;
+	Buffer		buffer = BufferDescriptorGetBuffer(buf_hdr);
+	int			bufid = -buffer - 1;
+
+	buf_state = pg_atomic_read_u32(&buf_hdr->state);
+
+	if (LocalRefCount[bufid] == 0)
+	{
+		if (adjust_usagecount &&
+			BUF_STATE_GET_USAGECOUNT(buf_state) < BM_MAX_USAGE_COUNT)
+		{
+			buf_state += BUF_USAGECOUNT_ONE;
+			pg_atomic_unlocked_write_u32(&buf_hdr->state, buf_state);
+		}
+	}
+	LocalRefCount[bufid]++;
+	ResourceOwnerRememberBuffer(CurrentResourceOwner,
+								BufferDescriptorGetBuffer(buf_hdr));
+
+	return buf_state & BM_VALID;
+}
+
+void
+UnpinLocalBuffer(Buffer buffer)
+{
+	int			buffid = -buffer - 1;
+
+	Assert(BufferIsLocal(buffer));
+	Assert(LocalRefCount[buffid] > 0);
+
+	ResourceOwnerForgetBuffer(CurrentResourceOwner, buffer);
+	LocalRefCount[buffid]--;
+}
+
 /*
  * GUC check_hook for temp_buffers
  */

src/include/storage/buf_internals.h

@@ -415,6 +415,8 @@ extern int	BufTableInsert(BufferTag *tagPtr, uint32 hashcode, int buf_id);
 extern void BufTableDelete(BufferTag *tagPtr, uint32 hashcode);
 
 /* localbuf.c */
+extern bool PinLocalBuffer(BufferDesc *buf_hdr, bool adjust_usagecount);
+extern void UnpinLocalBuffer(Buffer buffer);
 extern PrefetchBufferResult PrefetchLocalBuffer(SMgrRelation smgr,
 												ForkNumber forkNum,
 												BlockNumber blockNum);