Assorted minor doc/comment fixes.

Identify pg_replication_origin as a shared catalog in catalogs.sgml,
using the same boilerplate wording used for most other shared catalogs
(and tweak another place where someone had randomly deviated from
that boilerplate).

Make an example in mmgr/README more consistent with surrounding text.

Update an obsolete cross-reference in a comment in storage/block.h.

Zhuo Ql

Discussion: https://postgr.es/m/44296255.1819230.1524889719001@mail.yahoo.com

doc/src/sgml/catalogs.sgml

@@ -5690,6 +5690,13 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
    see <xref linkend="replication-origins"/>.
   </para>
 
+  <para>
+   Unlike most system catalogs, <structname>pg_replication_origin</structname>
+   is shared across all databases of a cluster: there is only one copy
+   of <structname>pg_replication_origin</structname> per cluster, not one per
+   database.
+  </para>
+
   <table>
 
    <title><structname>pg_replication_origin</structname> Columns</title>
@@ -6608,7 +6615,7 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
 
   <para>
    Unlike most system catalogs, <structname>pg_subscription</structname> is
-   shared across all databases of a cluster: There is only one copy
+   shared across all databases of a cluster: there is only one copy
    of <structname>pg_subscription</structname> per cluster, not one per
    database.
   </para>

src/backend/utils/mmgr/README

@@ -401,7 +401,7 @@ GetMemoryChunkContext())
 
 and then invoke the corresponding method for the context
 
-    context->methods->free_p(p);
+    context->methods->free_p(pointer);
 
 
 More Control Over aset.c Behavior

src/include/storage/block.h

@@ -22,7 +22,7 @@
  * contains exactly one disk block).  the blocks are numbered
  * sequentially, 0 to 0xFFFFFFFE.
  *
- * InvalidBlockNumber is the same thing as P_NEW in buf.h.
+ * InvalidBlockNumber is the same thing as P_NEW in bufmgr.h.
  *
  * the access methods, the buffer manager and the storage manager are
  * more or less the only pieces of code that should be accessing disk