diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c
index 3623352b9c..a3ba8cddba 100644
--- a/src/backend/access/transam/slru.c
+++ b/src/backend/access/transam/slru.c
@@ -120,6 +120,13 @@ typedef enum
 	SLRU_CLOSE_FAILED
 } SlruErrorCause;
 
+/*
+ * Static area used as placeholder for O_DIRECT operations.  Make sure
+ * to keep its size at twice the block size so as it would be aligned
+ * with the OS pages.
+ */
+static char direct_buf[BLCKSZ + BLCKSZ];
+
 static SlruErrorCause slru_errcause;
 static int	slru_errno;
 
@@ -644,6 +651,12 @@ SlruPhysicalReadPage(SlruCtl ctl, int pageno, int slotno)
 	int			offset = rpageno * BLCKSZ;
 	char		path[MAXPGPATH];
 	int			fd;
+	int			direct_flag = 0;
+	char	   *aligned_buf = (char *) TYPEALIGN(BLCKSZ, direct_buf);
+
+	/* Use direct I/O if configured as such */
+	if (direct_io)
+		direct_flag |= O_DIRECT | O_SYNC;
 
 	SlruFileName(ctl, path, segno);
 
@@ -654,7 +667,7 @@ SlruPhysicalReadPage(SlruCtl ctl, int pageno, int slotno)
 	 * SlruPhysicalWritePage).  Hence, if we are InRecovery, allow the case
 	 * where the file doesn't exist, and return zeroes instead.
 	 */
-	fd = OpenTransientFile(path, O_RDWR | PG_BINARY);
+	fd = OpenTransientFile(path, O_RDWR | PG_BINARY | direct_flag);
 	if (fd < 0)
 	{
 		if (errno != ENOENT || !InRecovery)
@@ -681,7 +694,7 @@ SlruPhysicalReadPage(SlruCtl ctl, int pageno, int slotno)
 
 	errno = 0;
 	pgstat_report_wait_start(WAIT_EVENT_SLRU_READ);
-	if (read(fd, shared->page_buffer[slotno], BLCKSZ) != BLCKSZ)
+	if (read(fd, aligned_buf, BLCKSZ) != BLCKSZ)
 	{
 		pgstat_report_wait_end();
 		slru_errcause = SLRU_READ_FAILED;
@@ -698,6 +711,9 @@ SlruPhysicalReadPage(SlruCtl ctl, int pageno, int slotno)
 		return false;
 	}
 
+	/* copy contents back to the slot */
+	memcpy(shared->page_buffer[slotno], aligned_buf, BLCKSZ);
+
 	return true;
 }
 
@@ -724,6 +740,12 @@ SlruPhysicalWritePage(SlruCtl ctl, int pageno, int slotno, SlruFlush fdata)
 	int			offset = rpageno * BLCKSZ;
 	char		path[MAXPGPATH];
 	int			fd = -1;
+	int			direct_flag = 0;
+	char	   *aligned_buf = (char *) TYPEALIGN(BLCKSZ, direct_buf);
+
+	/* Use direct I/O if configured as such */
+	if (direct_io)
+		direct_flag |= O_DIRECT | O_SYNC;
 
 	/*
 	 * Honor the write-WAL-before-data rule, if appropriate, so that we do not
@@ -804,7 +826,7 @@ SlruPhysicalWritePage(SlruCtl ctl, int pageno, int slotno, SlruFlush fdata)
 		 * don't use O_EXCL or O_TRUNC or anything like that.
 		 */
 		SlruFileName(ctl, path, segno);
-		fd = OpenTransientFile(path, O_RDWR | O_CREAT | PG_BINARY);
+		fd = OpenTransientFile(path, O_RDWR | O_CREAT | PG_BINARY | direct_flag);
 		if (fd < 0)
 		{
 			slru_errcause = SLRU_OPEN_FAILED;
@@ -840,9 +862,12 @@ SlruPhysicalWritePage(SlruCtl ctl, int pageno, int slotno, SlruFlush fdata)
 		return false;
 	}
 
+	/* use aligned buffer for O_DIRECT */
+	memcpy(aligned_buf, shared->page_buffer[slotno], BLCKSZ);
+
 	errno = 0;
 	pgstat_report_wait_start(WAIT_EVENT_SLRU_WRITE);
-	if (write(fd, shared->page_buffer[slotno], BLCKSZ) != BLCKSZ)
+	if (write(fd, aligned_buf, BLCKSZ) != BLCKSZ)
 	{
 		pgstat_report_wait_end();
 		/* if write didn't set errno, assume problem is no disk space */
@@ -858,12 +883,13 @@ SlruPhysicalWritePage(SlruCtl ctl, int pageno, int slotno, SlruFlush fdata)
 
 	/*
 	 * If not part of Flush, need to fsync now.  We assume this happens
-	 * infrequently enough that it's not a performance issue.
+	 * infrequently enough that it's not a performance issue.  O_DIRECT
+	 * has already made sure that this happens.
 	 */
 	if (!fdata)
 	{
 		pgstat_report_wait_start(WAIT_EVENT_SLRU_SYNC);
-		if (ctl->do_fsync && pg_fsync(fd))
+		if (!direct_io && ctl->do_fsync && pg_fsync(fd))
 		{
 			pgstat_report_wait_end();
 			slru_errcause = SLRU_FSYNC_FAILED;
diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index 213de7698a..92bcb57934 100644
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -148,6 +148,9 @@ int			max_safe_fds = 32;	/* default if not changed */
 /* Whether it is safe to continue running after fsync() fails. */
 bool		data_sync_retry = false;
 
+/* Use O_DIRECT for operations involving relation files and SLRUs */
+bool		direct_io = true;
+
 /* Debugging.... */
 
 #ifdef FDDEBUG
diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
index c37dd1290b..a927c8bd5a 100644
--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -159,6 +159,12 @@ static MemoryContext pendingOpsCxt; /* context for the above  */
 static CycleCtr mdsync_cycle_ctr = 0;
 static CycleCtr mdckpt_cycle_ctr = 0;
 
+/*
+ * Static area used as placeholder for O_DIRECT operations.  Make sure
+ * to keep its size at twice the block size so as it would be aligned
+ * with the OS pages.
+ */
+static char direct_buf[BLCKSZ + BLCKSZ];
 
 /*** behavior for mdopen & _mdfd_getseg ***/
 /* ereport if segment not present */
@@ -296,6 +302,7 @@ mdcreate(SMgrRelation reln, ForkNumber forkNum, bool isRedo)
 	MdfdVec    *mdfd;
 	char	   *path;
 	File		fd;
+	int			direct_flag = 0;
 
 	if (isRedo && reln->md_num_open_segs[forkNum] > 0)
 		return;					/* created and opened already... */
@@ -304,7 +311,11 @@ mdcreate(SMgrRelation reln, ForkNumber forkNum, bool isRedo)
 
 	path = relpath(reln->smgr_rnode, forkNum);
 
-	fd = PathNameOpenFile(path, O_RDWR | O_CREAT | O_EXCL | PG_BINARY);
+	/* Use direct I/O if configured as such */
+	if (direct_io)
+		direct_flag |= O_DIRECT | O_SYNC;
+
+	fd = PathNameOpenFile(path, O_RDWR | O_CREAT | O_EXCL | PG_BINARY | direct_flag);
 
 	if (fd < 0)
 	{
@@ -317,7 +328,7 @@ mdcreate(SMgrRelation reln, ForkNumber forkNum, bool isRedo)
 		 * already, even if isRedo is not set.  (See also mdopen)
 		 */
 		if (isRedo || IsBootstrapProcessingMode())
-			fd = PathNameOpenFile(path, O_RDWR | PG_BINARY);
+			fd = PathNameOpenFile(path, O_RDWR | PG_BINARY | direct_flag);
 		if (fd < 0)
 		{
 			/* be sure to report the error reported by create, not open */
@@ -498,12 +509,18 @@ mdextend(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 	off_t		seekpos;
 	int			nbytes;
 	MdfdVec    *v;
+	char	   *aligned_buf = (char *) TYPEALIGN(BLCKSZ, direct_buf);
 
 	/* This assert is too expensive to have on normally ... */
 #ifdef CHECK_WRITE_VS_EXTEND
 	Assert(blocknum >= mdnblocks(reln, forknum));
 #endif
 
+	/*
+	 * Copy contents into an aligned buffer for direct I/O.
+	 */
+	memcpy(aligned_buf, buffer, BLCKSZ);
+
 	/*
 	 * If a relation manages to grow to 2^32-1 blocks, refuse to extend it any
 	 * more --- we mustn't create a block whose number actually is
@@ -522,7 +539,8 @@ mdextend(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 
 	Assert(seekpos < (off_t) BLCKSZ * RELSEG_SIZE);
 
-	if ((nbytes = FileWrite(v->mdfd_vfd, buffer, BLCKSZ, seekpos, WAIT_EVENT_DATA_FILE_EXTEND)) != BLCKSZ)
+	if ((nbytes = FileWrite(v->mdfd_vfd, aligned_buf, BLCKSZ, seekpos,
+							WAIT_EVENT_DATA_FILE_EXTEND)) != BLCKSZ)
 	{
 		if (nbytes < 0)
 			ereport(ERROR,
@@ -561,6 +579,7 @@ mdopen(SMgrRelation reln, ForkNumber forknum, int behavior)
 	MdfdVec    *mdfd;
 	char	   *path;
 	File		fd;
+	int			direct_flag = 0;
 
 	/* No work if already open */
 	if (reln->md_num_open_segs[forknum] > 0)
@@ -568,7 +587,11 @@ mdopen(SMgrRelation reln, ForkNumber forknum, int behavior)
 
 	path = relpath(reln->smgr_rnode, forknum);
 
-	fd = PathNameOpenFile(path, O_RDWR | PG_BINARY);
+	/* Use direct I/O if configured as such */
+	if (direct_io)
+		direct_flag |= O_DIRECT | O_SYNC;
+
+	fd = PathNameOpenFile(path, O_RDWR | PG_BINARY | direct_flag);
 
 	if (fd < 0)
 	{
@@ -579,7 +602,8 @@ mdopen(SMgrRelation reln, ForkNumber forknum, int behavior)
 		 * substitute for mdcreate() in bootstrap mode only. (See mdcreate)
 		 */
 		if (IsBootstrapProcessingMode())
-			fd = PathNameOpenFile(path, O_RDWR | O_CREAT | O_EXCL | PG_BINARY);
+			fd = PathNameOpenFile(path,
+					O_RDWR | O_CREAT | O_EXCL | PG_BINARY | direct_flag);
 		if (fd < 0)
 		{
 			if ((behavior & EXTENSION_RETURN_NULL) &&
@@ -719,6 +743,7 @@ mdread(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 	off_t		seekpos;
 	int			nbytes;
 	MdfdVec    *v;
+	char	   *aligned_buf = (char *) TYPEALIGN(BLCKSZ, direct_buf);
 
 	TRACE_POSTGRESQL_SMGR_MD_READ_START(forknum, blocknum,
 										reln->smgr_rnode.node.spcNode,
@@ -733,7 +758,8 @@ mdread(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 
 	Assert(seekpos < (off_t) BLCKSZ * RELSEG_SIZE);
 
-	nbytes = FileRead(v->mdfd_vfd, buffer, BLCKSZ, seekpos, WAIT_EVENT_DATA_FILE_READ);
+	nbytes = FileRead(v->mdfd_vfd, aligned_buf, BLCKSZ, seekpos,
+					  WAIT_EVENT_DATA_FILE_READ);
 
 	TRACE_POSTGRESQL_SMGR_MD_READ_DONE(forknum, blocknum,
 									   reln->smgr_rnode.node.spcNode,
@@ -760,7 +786,7 @@ mdread(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 		 * update a block that was later truncated away.
 		 */
 		if (zero_damaged_pages || InRecovery)
-			MemSet(buffer, 0, BLCKSZ);
+			MemSet(aligned_buf, 0, BLCKSZ);
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_DATA_CORRUPTED),
@@ -768,6 +794,11 @@ mdread(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 							blocknum, FilePathName(v->mdfd_vfd),
 							nbytes, BLCKSZ)));
 	}
+
+	/*
+	 * Copy the result from the aligned buffer to the real one.
+	 */
+	memcpy(buffer, aligned_buf, BLCKSZ);
 }
 
 /*
@@ -784,12 +815,18 @@ mdwrite(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 	off_t		seekpos;
 	int			nbytes;
 	MdfdVec    *v;
+	char	   *aligned_buf = (char *) TYPEALIGN(BLCKSZ, direct_buf);
 
 	/* This assert is too expensive to have on normally ... */
 #ifdef CHECK_WRITE_VS_EXTEND
 	Assert(blocknum < mdnblocks(reln, forknum));
 #endif
 
+	/*
+	 * Copy contents into an aligned buffer for direct I/O.
+	 */
+	memcpy(aligned_buf, buffer, BLCKSZ);
+
 	TRACE_POSTGRESQL_SMGR_MD_WRITE_START(forknum, blocknum,
 										 reln->smgr_rnode.node.spcNode,
 										 reln->smgr_rnode.node.dbNode,
@@ -803,7 +840,8 @@ mdwrite(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 
 	Assert(seekpos < (off_t) BLCKSZ * RELSEG_SIZE);
 
-	nbytes = FileWrite(v->mdfd_vfd, buffer, BLCKSZ, seekpos, WAIT_EVENT_DATA_FILE_WRITE);
+	nbytes = FileWrite(v->mdfd_vfd, aligned_buf, BLCKSZ, seekpos,
+					   WAIT_EVENT_DATA_FILE_WRITE);
 
 	TRACE_POSTGRESQL_SMGR_MD_WRITE_DONE(forknum, blocknum,
 										reln->smgr_rnode.node.spcNode,
@@ -1011,11 +1049,14 @@ mdimmedsync(SMgrRelation reln, ForkNumber forknum)
 	{
 		MdfdVec    *v = &reln->md_seg_fds[forknum][segno - 1];
 
-		if (FileSync(v->mdfd_vfd, WAIT_EVENT_DATA_FILE_IMMEDIATE_SYNC) < 0)
+		/* nothing to do with direct I/O */
+		if (!direct_io &&
+			FileSync(v->mdfd_vfd, WAIT_EVENT_DATA_FILE_IMMEDIATE_SYNC) < 0)
 			ereport(data_sync_elevel(ERROR),
 					(errcode_for_file_access(),
 					 errmsg("could not fsync file \"%s\": %m",
 							FilePathName(v->mdfd_vfd))));
+
 		segno--;
 	}
 }
@@ -1414,9 +1455,15 @@ mdpostckpt(void)
 static void
 register_dirty_segment(SMgrRelation reln, ForkNumber forknum, MdfdVec *seg)
 {
+	return;
+
 	/* Temp relations should never be fsync'd */
 	Assert(!SmgrIsTemp(reln));
 
+	/* Not actually needed with direct I/O */
+	if (direct_io)
+		return;
+
 	if (pendingOpsTable)
 	{
 		/* push it into local pending-ops table */
@@ -1799,11 +1846,16 @@ _mdfd_openseg(SMgrRelation reln, ForkNumber forknum, BlockNumber segno,
 	MdfdVec    *v;
 	int			fd;
 	char	   *fullpath;
+	int			direct_flag = 0;
 
 	fullpath = _mdfd_segpath(reln, forknum, segno);
 
+	/* Use direct I/O if configured as such */
+	if (direct_io)
+		direct_flag |= O_DIRECT | O_SYNC;
+
 	/* open the file */
-	fd = PathNameOpenFile(fullpath, O_RDWR | PG_BINARY | oflags);
+	fd = PathNameOpenFile(fullpath, O_RDWR | PG_BINARY | direct_flag | oflags);
 
 	pfree(fullpath);
 
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index f81e0424e7..a0809ad628 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -631,6 +631,8 @@ const char *const config_group_names[] =
 	gettext_noop("Resource Usage / Background Writer"),
 	/* RESOURCES_ASYNCHRONOUS */
 	gettext_noop("Resource Usage / Asynchronous Behavior"),
+	/* RESOURCES_IO */
+	gettext_noop("Resource Usage / I/O"),
 	/* WAL */
 	gettext_noop("Write-Ahead Log"),
 	/* WAL_SETTINGS */
@@ -1875,6 +1877,15 @@ static struct config_bool ConfigureNamesBool[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"direct_io", PGC_POSTMASTER, RESOURCES_IO,
+			gettext_noop("Use direct I/O when flushing relations and SLRUs."),
+		},
+		&direct_io,
+		true,
+		NULL, NULL, NULL
+	},
+
 	/* End-of-list marker */
 	{
 		{NULL, 0, 0, NULL, NULL}, NULL, false, NULL, NULL, NULL
diff --git a/src/include/storage/fd.h b/src/include/storage/fd.h
index 74c34757fb..ecaa347657 100644
--- a/src/include/storage/fd.h
+++ b/src/include/storage/fd.h
@@ -48,6 +48,7 @@ typedef int File;
 /* GUC parameter */
 extern PGDLLIMPORT int max_files_per_process;
 extern PGDLLIMPORT bool data_sync_retry;
+extern PGDLLIMPORT bool direct_io;
 
 /*
  * This is private to fd.c, but exported for save/restore_backend_variables()
diff --git a/src/include/utils/guc_tables.h b/src/include/utils/guc_tables.h
index a0970b2e1c..17178862a7 100644
--- a/src/include/utils/guc_tables.h
+++ b/src/include/utils/guc_tables.h
@@ -65,6 +65,7 @@ enum config_group
 	RESOURCES_VACUUM_DELAY,
 	RESOURCES_BGWRITER,
 	RESOURCES_ASYNCHRONOUS,
+	RESOURCES_IO,
 	WAL,
 	WAL_SETTINGS,
 	WAL_CHECKPOINTS,