From 4557d9f70bf051beb8622de086756505bce684b8 Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Tue, 4 Mar 2025 10:44:56 -0500
Subject: [PATCH v2.5 01/30] aio: Basic subsystem initialization

This is just separate to make it easier to review the tendrils into various
places.  It will likely be merged with the subsequent commit before being
merged.
---
 src/include/storage/aio.h                     | 38 +++++++++++
 src/include/storage/aio_subsys.h              | 28 ++++++++
 src/include/utils/guc.h                       |  1 +
 src/include/utils/guc_hooks.h                 |  2 +
 src/include/utils/resowner.h                  |  5 ++
 src/backend/storage/aio/Makefile              |  2 +
 src/backend/storage/aio/aio.c                 | 67 +++++++++++++++++++
 src/backend/storage/aio/aio_init.c            | 37 ++++++++++
 src/backend/storage/aio/meson.build           |  2 +
 src/backend/storage/ipc/ipci.c                |  3 +
 src/backend/utils/init/postinit.c             |  7 ++
 src/backend/utils/misc/guc_tables.c           | 23 +++++++
 src/backend/utils/misc/postgresql.conf.sample |  6 ++
 src/backend/utils/resowner/resowner.c         | 29 ++++++++
 doc/src/sgml/config.sgml                      | 51 ++++++++++++++
 src/tools/pgindent/typedefs.list              |  1 +
 16 files changed, 302 insertions(+)
 create mode 100644 src/include/storage/aio.h
 create mode 100644 src/include/storage/aio_subsys.h
 create mode 100644 src/backend/storage/aio/aio.c
 create mode 100644 src/backend/storage/aio/aio_init.c

diff --git a/src/include/storage/aio.h b/src/include/storage/aio.h
new file mode 100644
index 00000000000..e79d5343038
--- /dev/null
+++ b/src/include/storage/aio.h
@@ -0,0 +1,38 @@
+/*-------------------------------------------------------------------------
+ *
+ * aio.h
+ *    Main AIO interface
+ *
+ *
+ * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/aio.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef AIO_H
+#define AIO_H
+
+
+
+/* Enum for io_method GUC. */
+typedef enum IoMethod
+{
+	IOMETHOD_SYNC = 0,
+} IoMethod;
+
+/* We'll default to synchronous execution. */
+#define DEFAULT_IO_METHOD IOMETHOD_SYNC
+
+
+struct dlist_node;
+extern void pgaio_io_release_resowner(struct dlist_node *ioh_node, bool on_error);
+
+
+/* GUCs */
+extern PGDLLIMPORT int io_method;
+extern PGDLLIMPORT int io_max_concurrency;
+
+
+#endif							/* AIO_H */
diff --git a/src/include/storage/aio_subsys.h b/src/include/storage/aio_subsys.h
new file mode 100644
index 00000000000..0b8aaaf00d3
--- /dev/null
+++ b/src/include/storage/aio_subsys.h
@@ -0,0 +1,28 @@
+/*-------------------------------------------------------------------------
+ *
+ * aio_subsys.h
+ *    Interaction with AIO as a subsystem, rather than actually issuing AIO
+ *
+ * This header is for AIO related functionality that's being called by files
+ * that don't perform AIO but interact with it in some form. E.g. postmaster.c
+ * and shared memory initialization need to initialize AIO but don't perform
+ * AIO.
+ *
+ * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/aio_subsys.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef AIO_SUBSYS_H
+#define AIO_SUBSYS_H
+
+
+/* aio_init.c */
+extern Size AioShmemSize(void);
+extern void AioShmemInit(void);
+
+extern void pgaio_init_backend(void);
+
+#endif							/* AIO_SUBSYS_H */
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index 1233e07d7da..de3bc37264f 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -318,6 +318,7 @@ extern PGDLLIMPORT bool optimize_bounded_sort;
  */
 extern PGDLLIMPORT const struct config_enum_entry archive_mode_options[];
 extern PGDLLIMPORT const struct config_enum_entry dynamic_shared_memory_options[];
+extern PGDLLIMPORT const struct config_enum_entry io_method_options[];
 extern PGDLLIMPORT const struct config_enum_entry recovery_target_action_options[];
 extern PGDLLIMPORT const struct config_enum_entry wal_level_options[];
 extern PGDLLIMPORT const struct config_enum_entry wal_sync_method_options[];
diff --git a/src/include/utils/guc_hooks.h b/src/include/utils/guc_hooks.h
index 951451a9765..d1b49adc547 100644
--- a/src/include/utils/guc_hooks.h
+++ b/src/include/utils/guc_hooks.h
@@ -62,6 +62,8 @@ extern bool check_default_with_oids(bool *newval, void **extra,
 extern bool check_effective_io_concurrency(int *newval, void **extra,
 										   GucSource source);
 extern bool check_huge_page_size(int *newval, void **extra, GucSource source);
+extern void assign_io_method(int newval, void *extra);
+extern bool check_io_max_concurrency(int *newval, void **extra, GucSource source);
 extern const char *show_in_hot_standby(void);
 extern bool check_locale_messages(char **newval, void **extra, GucSource source);
 extern void assign_locale_messages(const char *newval, void *extra);
diff --git a/src/include/utils/resowner.h b/src/include/utils/resowner.h
index e8d452ca7ee..aede4bfc820 100644
--- a/src/include/utils/resowner.h
+++ b/src/include/utils/resowner.h
@@ -164,4 +164,9 @@ struct LOCALLOCK;
 extern void ResourceOwnerRememberLock(ResourceOwner owner, struct LOCALLOCK *locallock);
 extern void ResourceOwnerForgetLock(ResourceOwner owner, struct LOCALLOCK *locallock);
 
+/* special support for AIO */
+struct dlist_node;
+extern void ResourceOwnerRememberAioHandle(ResourceOwner owner, struct dlist_node *ioh_node);
+extern void ResourceOwnerForgetAioHandle(ResourceOwner owner, struct dlist_node *ioh_node);
+
 #endif							/* RESOWNER_H */
diff --git a/src/backend/storage/aio/Makefile b/src/backend/storage/aio/Makefile
index 2f29a9ec4d1..eaeaeeee8e3 100644
--- a/src/backend/storage/aio/Makefile
+++ b/src/backend/storage/aio/Makefile
@@ -9,6 +9,8 @@ top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
 OBJS = \
+	aio.o \
+	aio_init.o \
 	read_stream.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/storage/aio/aio.c b/src/backend/storage/aio/aio.c
new file mode 100644
index 00000000000..8eb6a5f1292
--- /dev/null
+++ b/src/backend/storage/aio/aio.c
@@ -0,0 +1,67 @@
+/*-------------------------------------------------------------------------
+ *
+ * aio.c
+ *    AIO - Core Logic
+ *
+ * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *    src/backend/storage/aio/aio.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "lib/ilist.h"
+#include "storage/aio.h"
+#include "utils/guc.h"
+#include "utils/guc_hooks.h"
+
+
+/* Options for io_method. */
+const struct config_enum_entry io_method_options[] = {
+	{"sync", IOMETHOD_SYNC, false},
+	{NULL, 0, false}
+};
+
+/* GUCs */
+int			io_method = DEFAULT_IO_METHOD;
+int			io_max_concurrency = -1;
+
+
+
+void
+assign_io_method(int newval, void *extra)
+{
+}
+
+bool
+check_io_max_concurrency(int *newval, void **extra, GucSource source)
+{
+	if (*newval == -1)
+	{
+		/*
+		 * Auto-tuning will be applied later during startup, as auto-tuning
+		 * depends on the value of various GUCs.
+		 */
+		return true;
+	}
+	else if (*newval == 0)
+	{
+		GUC_check_errdetail("Only -1 or values bigger than 0 are valid.");
+		return false;
+	}
+
+	return true;
+}
+
+/*
+ * Release IO handle during resource owner cleanup.
+ */
+void
+pgaio_io_release_resowner(dlist_node *ioh_node, bool on_error)
+{
+	/* placeholder for later */
+}
diff --git a/src/backend/storage/aio/aio_init.c b/src/backend/storage/aio/aio_init.c
new file mode 100644
index 00000000000..aeacc144149
--- /dev/null
+++ b/src/backend/storage/aio/aio_init.c
@@ -0,0 +1,37 @@
+/*-------------------------------------------------------------------------
+ *
+ * aio_init.c
+ *    AIO - Subsystem Initialization
+ *
+ * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *    src/backend/storage/aio/aio_init.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "storage/aio_subsys.h"
+
+
+
+Size
+AioShmemSize(void)
+{
+	Size		sz = 0;
+
+	return sz;
+}
+
+void
+AioShmemInit(void)
+{
+}
+
+void
+pgaio_init_backend(void)
+{
+}
diff --git a/src/backend/storage/aio/meson.build b/src/backend/storage/aio/meson.build
index 8abe0eb4863..c822fd4ddf7 100644
--- a/src/backend/storage/aio/meson.build
+++ b/src/backend/storage/aio/meson.build
@@ -1,5 +1,7 @@
 # Copyright (c) 2024-2025, PostgreSQL Global Development Group
 
 backend_sources += files(
+  'aio.c',
+  'aio_init.c',
   'read_stream.c',
 )
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 174eed70367..2fa045e6b0f 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -37,6 +37,7 @@
 #include "replication/slotsync.h"
 #include "replication/walreceiver.h"
 #include "replication/walsender.h"
+#include "storage/aio_subsys.h"
 #include "storage/bufmgr.h"
 #include "storage/dsm.h"
 #include "storage/dsm_registry.h"
@@ -148,6 +149,7 @@ CalculateShmemSize(int *num_semaphores)
 	size = add_size(size, WaitEventCustomShmemSize());
 	size = add_size(size, InjectionPointShmemSize());
 	size = add_size(size, SlotSyncShmemSize());
+	size = add_size(size, AioShmemSize());
 
 	/* include additional requested shmem from preload libraries */
 	size = add_size(size, total_addin_request);
@@ -340,6 +342,7 @@ CreateOrAttachShmemStructs(void)
 	StatsShmemInit();
 	WaitEventCustomShmemInit();
 	InjectionPointShmemInit();
+	AioShmemInit();
 }
 
 /*
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index b428a59bdd2..ad1fb624e3c 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -43,6 +43,7 @@
 #include "replication/slot.h"
 #include "replication/slotsync.h"
 #include "replication/walsender.h"
+#include "storage/aio_subsys.h"
 #include "storage/bufmgr.h"
 #include "storage/fd.h"
 #include "storage/ipc.h"
@@ -628,6 +629,12 @@ BaseInit(void)
 	 */
 	pgstat_initialize();
 
+	/*
+	 * Initialize AIO before infrastructure that might need to actually
+	 * execute AIO.
+	 */
+	pgaio_init_backend();
+
 	/* Do local initialization of storage and buffer managers */
 	InitSync();
 	smgrinit();
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index ad25cbb39c5..28dcc465762 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -72,6 +72,7 @@
 #include "replication/slot.h"
 #include "replication/slotsync.h"
 #include "replication/syncrep.h"
+#include "storage/aio.h"
 #include "storage/bufmgr.h"
 #include "storage/bufpage.h"
 #include "storage/large_object.h"
@@ -3254,6 +3255,18 @@ struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"io_max_concurrency",
+			PGC_POSTMASTER,
+			RESOURCES_IO,
+			gettext_noop("Max number of IOs that one process can execute simultaneously."),
+			NULL,
+		},
+		&io_max_concurrency,
+		-1, -1, 1024,
+		check_io_max_concurrency, NULL, NULL
+	},
+
 	{
 		{"backend_flush_after", PGC_USERSET, RESOURCES_IO,
 			gettext_noop("Number of pages after which previously performed writes are flushed to disk."),
@@ -5299,6 +5312,16 @@ struct config_enum ConfigureNamesEnum[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"io_method", PGC_POSTMASTER, RESOURCES_IO,
+			gettext_noop("Selects the method for executing asynchronous I/O."),
+			NULL
+		},
+		&io_method,
+		DEFAULT_IO_METHOD, io_method_options,
+		NULL, assign_io_method, NULL
+	},
+
 	/* End-of-list marker */
 	{
 		{NULL, 0, 0, NULL, NULL}, NULL, 0, NULL, NULL, NULL, NULL
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 2d1de9c37bd..a31c9963ce4 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -202,6 +202,12 @@
 #maintenance_io_concurrency = 10	# 1-1000; 0 disables prefetching
 #io_combine_limit = 128kB		# usually 1-32 blocks (depends on OS)
 
+#io_method = sync			# sync (change requires restart)
+#io_max_concurrency = -1		# Max number of IOs that one process
+					# can execute simultaneously
+					# -1 sets based on shared_buffers
+					# (change requires restart)
+
 # - Worker Processes -
 
 #max_worker_processes = 8		# (change requires restart)
diff --git a/src/backend/utils/resowner/resowner.c b/src/backend/utils/resowner/resowner.c
index ac5ca4a765e..76b9cec1e26 100644
--- a/src/backend/utils/resowner/resowner.c
+++ b/src/backend/utils/resowner/resowner.c
@@ -47,6 +47,8 @@
 
 #include "common/hashfn.h"
 #include "common/int.h"
+#include "lib/ilist.h"
+#include "storage/aio.h"
 #include "storage/ipc.h"
 #include "storage/predicate.h"
 #include "storage/proc.h"
@@ -155,6 +157,12 @@ struct ResourceOwnerData
 
 	/* The local locks cache. */
 	LOCALLOCK  *locks[MAX_RESOWNER_LOCKS];	/* list of owned locks */
+
+	/*
+	 * AIO handles need be registered in critical sections and therefore
+	 * cannot use the normal ResoureElem mechanism.
+	 */
+	dlist_head	aio_handles;
 };
 
 
@@ -425,6 +433,8 @@ ResourceOwnerCreate(ResourceOwner parent, const char *name)
 		parent->firstchild = owner;
 	}
 
+	dlist_init(&owner->aio_handles);
+
 	return owner;
 }
 
@@ -725,6 +735,13 @@ ResourceOwnerReleaseInternal(ResourceOwner owner,
 		 * so issue warnings.  In the abort case, just clean up quietly.
 		 */
 		ResourceOwnerReleaseAll(owner, phase, isCommit);
+
+		while (!dlist_is_empty(&owner->aio_handles))
+		{
+			dlist_node *node = dlist_head_node(&owner->aio_handles);
+
+			pgaio_io_release_resowner(node, !isCommit);
+		}
 	}
 	else if (phase == RESOURCE_RELEASE_LOCKS)
 	{
@@ -1082,3 +1099,15 @@ ResourceOwnerForgetLock(ResourceOwner owner, LOCALLOCK *locallock)
 	elog(ERROR, "lock reference %p is not owned by resource owner %s",
 		 locallock, owner->name);
 }
+
+void
+ResourceOwnerRememberAioHandle(ResourceOwner owner, struct dlist_node *ioh_node)
+{
+	dlist_push_tail(&owner->aio_handles, ioh_node);
+}
+
+void
+ResourceOwnerForgetAioHandle(ResourceOwner owner, struct dlist_node *ioh_node)
+{
+	dlist_delete_from(&owner->aio_handles, ioh_node);
+}
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d2fa5f7d1a9..7d5482f31cd 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -2644,6 +2644,57 @@ include_dir 'conf.d'
         </para>
        </listitem>
       </varlistentry>
+
+      <varlistentry id="guc-io-max-concurrency" xreflabel="io_max_concurrency">
+       <term><varname>io_max_concurrency</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>io_max_concurrency</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Controls the maximum number of I/O operations that one process can
+         execute simultaneously.
+        </para>
+        <para>
+         The default setting of <literal>-1</literal> selects a number based
+         on <xref linkend="guc-shared-buffers"/> and the maximum number of
+         processes (<xref linkend="guc-max-connections"/>, <xref
+         linkend="guc-autovacuum-worker-slots"/>, <xref
+         linkend="guc-max-worker-processes"/> and <xref
+         linkend="guc-max-wal-senders"/>), but not more than
+         <literal>64</literal>.
+        </para>
+        <para>
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry id="guc-io-method" xreflabel="io_method">
+       <term><varname>io_method</varname> (<type>enum</type>)
+       <indexterm>
+        <primary><varname>io_method</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Selects the method for executing asynchronous I/O.
+         Possible values are:
+         <itemizedlist>
+          <listitem>
+           <para>
+            <literal>sync</literal> (execute asynchronous I/O synchronously)
+           </para>
+          </listitem>
+         </itemizedlist>
+        </para>
+        <para>
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
      </variablelist>
     </sect2>
 
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 19ff271ba50..c80365974e4 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -1276,6 +1276,7 @@ IntoClause
 InvalMessageArray
 InvalidationInfo
 InvalidationMsgsGroup
+IoMethod
 IpcMemoryId
 IpcMemoryKey
 IpcMemoryState
-- 
2.48.1.76.g4e746b1a31.dirty

