Revert no-op changes to BufferGetPage()

The reverted changes were intended to force a choice of whether any
newly-added BufferGetPage() calls needed to be accompanied by a
test of the snapshot age, to support the "snapshot too old"
feature.  Such an accompanying test is needed in about 7% of the
cases, where the page is being used as part of a scan rather than
positioning for other purposes (such as DML or vacuuming).  The
additional effort required for back-patching, and the doubt whether
the intended benefit would really be there, have indicated it is
best just to rely on developers to do the right thing based on
comments and existing usage, as we do with many other conventions.

This change should have little or no effect on generated executable
code.

Motivated by the back-patching pain of Tom Lane and Robert Haas

src/backend/storage/buffer/bufmgr.c

@@ -2815,7 +2815,7 @@ XLogRecPtr
 BufferGetLSNAtomic(Buffer buffer)
 {
 	BufferDesc *bufHdr = GetBufferDescriptor(buffer - 1);
-	char	   *page = BufferGetPage(buffer, NULL, NULL, BGP_NO_SNAPSHOT_TEST);
+	char	   *page = BufferGetPage(buffer);
 	XLogRecPtr	lsn;
 	uint32		buf_state;
 
@@ -3362,7 +3362,7 @@ void
 MarkBufferDirtyHint(Buffer buffer, bool buffer_std)
 {
 	BufferDesc *bufHdr;
-	Page		page = BufferGetPage(buffer, NULL, NULL, BGP_NO_SNAPSHOT_TEST);
+	Page		page = BufferGetPage(buffer);
 
 	if (!BufferIsValid(buffer))
 		elog(ERROR, "bad buffer ID: %d", buffer);
@@ -4288,10 +4288,8 @@ IssuePendingWritebacks(WritebackContext *context)
  * This test generally needs to be performed after every BufferGetPage() call
  * that is executed as part of a scan.  It is not needed for calls made for
  * modifying the page (for example, to position to the right place to insert a
- * new index tuple or for vacuuming).  To minimize errors of omission, the
- * BufferGetPage() macro accepts parameters to specify whether the test should
- * be run, and supply the necessary snapshot and relation parameters.  See the
- * declaration of BufferGetPage() for more details.
+ * new index tuple or for vacuuming).  It may also be omitted where calls to
+ * lower-level functions will have already performed the test.
  *
  * Note that a NULL snapshot argument is allowed and causes a fast return
  * without error; this is to support call sites which can be called from

src/backend/storage/freespace/freespace.c

@@ -253,7 +253,7 @@ XLogRecordPageWithFreeSpace(RelFileNode rnode, BlockNumber heapBlk,
 	buf = XLogReadBufferExtended(rnode, FSM_FORKNUM, blkno, RBM_ZERO_ON_ERROR);
 	LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
 
-	page = BufferGetPage(buf, NULL, NULL, BGP_NO_SNAPSHOT_TEST);
+	page = BufferGetPage(buf);
 	if (PageIsNew(page))
 		PageInit(page, BLCKSZ, 0);
 
@@ -280,8 +280,7 @@ GetRecordedFreeSpace(Relation rel, BlockNumber heapBlk)
 	buf = fsm_readbuf(rel, addr, false);
 	if (!BufferIsValid(buf))
 		return 0;
-	cat = fsm_get_avail(BufferGetPage(buf, NULL, NULL, BGP_NO_SNAPSHOT_TEST),
-						slot);
+	cat = fsm_get_avail(BufferGetPage(buf), slot);
 	ReleaseBuffer(buf);
 
 	return fsm_space_cat_to_avail(cat);
@@ -328,9 +327,7 @@ FreeSpaceMapTruncateRel(Relation rel, BlockNumber nblocks)
 		if (!BufferIsValid(buf))
 			return;				/* nothing to do; the FSM was already smaller */
 		LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
-		fsm_truncate_avail(BufferGetPage(buf, NULL, NULL,
-										 BGP_NO_SNAPSHOT_TEST),
-						   first_removed_slot);
+		fsm_truncate_avail(BufferGetPage(buf), first_removed_slot);
 		MarkBufferDirtyHint(buf, false);
 		UnlockReleaseBuffer(buf);
 
@@ -580,9 +577,8 @@ fsm_readbuf(Relation rel, FSMAddress addr, bool extend)
 	 * headers, for example.
 	 */
 	buf = ReadBufferExtended(rel, FSM_FORKNUM, blkno, RBM_ZERO_ON_ERROR, NULL);
-	if (PageIsNew(BufferGetPage(buf, NULL, NULL, BGP_NO_SNAPSHOT_TEST)))
-		PageInit(BufferGetPage(buf, NULL, NULL, BGP_NO_SNAPSHOT_TEST),
-				 BLCKSZ, 0);
+	if (PageIsNew(BufferGetPage(buf)))
+		PageInit(BufferGetPage(buf), BLCKSZ, 0);
 	return buf;
 }
 
@@ -661,7 +657,7 @@ fsm_set_and_search(Relation rel, FSMAddress addr, uint16 slot,
 	buf = fsm_readbuf(rel, addr, true);
 	LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
 
-	page = BufferGetPage(buf, NULL, NULL, BGP_NO_SNAPSHOT_TEST);
+	page = BufferGetPage(buf);
 
 	if (fsm_set_avail(page, slot, newValue))
 		MarkBufferDirtyHint(buf, false);
@@ -705,9 +701,7 @@ fsm_search(Relation rel, uint8 min_cat)
 									(addr.level == FSM_BOTTOM_LEVEL),
 									false);
 			if (slot == -1)
-				max_avail =
-					fsm_get_max_avail(BufferGetPage(buf, NULL, NULL,
-													BGP_NO_SNAPSHOT_TEST));
+				max_avail = fsm_get_max_avail(BufferGetPage(buf));
 			UnlockReleaseBuffer(buf);
 		}
 		else
@@ -789,7 +783,7 @@ fsm_vacuum_page(Relation rel, FSMAddress addr, bool *eof_p)
 	else
 		*eof_p = false;
 
-	page = BufferGetPage(buf, NULL, NULL, BGP_NO_SNAPSHOT_TEST);
+	page = BufferGetPage(buf);
 
 	/*
 	 * Recurse into children, and fix the information stored about them at
@@ -816,17 +810,14 @@ fsm_vacuum_page(Relation rel, FSMAddress addr, bool *eof_p)
 			if (fsm_get_avail(page, slot) != child_avail)
 			{
 				LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
-				fsm_set_avail(BufferGetPage(buf, NULL, NULL,
-											BGP_NO_SNAPSHOT_TEST),
-							  slot, child_avail);
+				fsm_set_avail(BufferGetPage(buf), slot, child_avail);
 				MarkBufferDirtyHint(buf, false);
 				LockBuffer(buf, BUFFER_LOCK_UNLOCK);
 			}
 		}
 	}
 
-	max_avail = fsm_get_max_avail(BufferGetPage(buf, NULL, NULL,
-												BGP_NO_SNAPSHOT_TEST));
+	max_avail = fsm_get_max_avail(BufferGetPage(buf));
 
 	/*
 	 * Reset the next slot pointer. This encourages the use of low-numbered

src/backend/storage/freespace/fsmpage.c

@@ -158,7 +158,7 @@ int
 fsm_search_avail(Buffer buf, uint8 minvalue, bool advancenext,
 				 bool exclusive_lock_held)
 {
-	Page		page = BufferGetPage(buf, NULL, NULL, BGP_NO_SNAPSHOT_TEST);
+	Page		page = BufferGetPage(buf);
 	FSMPage		fsmpage = (FSMPage) PageGetContents(page);
 	int			nodeno;
 	int			target;