1 files changed, 45 insertions, 17 deletions

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 198a6985bf3..203555822d9 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -32,6 +32,7 @@
 #endif
 
 #include "miscadmin.h"
+#include "port/pg_bitutils.h"
 #include "portability/mem.h"
 #include "storage/dsm.h"
 #include "storage/fd.h"
@@ -448,7 +449,7 @@ PGSharedMemoryAttach(IpcMemoryId shmId,
 #ifdef MAP_HUGETLB
 
 /*
- * Identify the huge page size to use.
+ * Identify the huge page size to use, and compute the related mmap flags.
  *
  * Some Linux kernel versions have a bug causing mmap() to fail on requests
  * that are not a multiple of the hugepage size.  Versions without that bug
@@ -464,25 +465,13 @@ PGSharedMemoryAttach(IpcMemoryId shmId,
  * hugepage sizes, we might want to think about more invasive strategies,
  * such as increasing shared_buffers to absorb the extra space.
  *
- * Returns the (real or assumed) page size into *hugepagesize,
+ * Returns the (real, assumed or config provided) page size into *hugepagesize,
  * and the hugepage-related mmap flags to use into *mmap_flags.
- *
- * Currently *mmap_flags is always just MAP_HUGETLB.  Someday, on systems
- * that support it, we might OR in additional bits to specify a particular
- * non-default huge page size.
  */
 static void
 GetHugePageSize(Size *hugepagesize, int *mmap_flags)
 {
-	/*
-	 * If we fail to find out the system's default huge page size, assume it
-	 * is 2MB.  This will work fine when the actual size is less.  If it's
-	 * more, we might get mmap() or munmap() failures due to unaligned
-	 * requests; but at this writing, there are no reports of any non-Linux
-	 * systems being picky about that.
-	 */
-	*hugepagesize = 2 * 1024 * 1024;
-	*mmap_flags = MAP_HUGETLB;
+	Size		default_hugepagesize = 0;
 
 	/*
 	 * System-dependent code to find out the default huge page size.
@@ -491,6 +480,7 @@ GetHugePageSize(Size *hugepagesize, int *mmap_flags)
 	 * nnnn kB".  Ignore any failures, falling back to the preset default.
 	 */
 #ifdef __linux__
+
 	{
 		FILE	   *fp = AllocateFile("/proc/meminfo", "r");
 		char		buf[128];
@@ -505,7 +495,7 @@ GetHugePageSize(Size *hugepagesize, int *mmap_flags)
 				{
 					if (ch == 'k')
 					{
-						*hugepagesize = sz * (Size) 1024;
+						default_hugepagesize = sz * (Size) 1024;
 						break;
 					}
 					/* We could accept other units besides kB, if needed */
@@ -515,6 +505,44 @@ GetHugePageSize(Size *hugepagesize, int *mmap_flags)
 		}
 	}
 #endif							/* __linux__ */
+
+	if (huge_page_size != 0)
+	{
+		/* If huge page size is requested explicitly, use that. */
+		*hugepagesize = (Size) huge_page_size * 1024;
+	}
+	else if (default_hugepagesize != 0)
+	{
+		/* Otherwise use the system default, if we have it. */
+		*hugepagesize = default_hugepagesize;
+	}
+	else
+	{
+		/*
+		 * If we fail to find out the system's default huge page size, or no
+		 * huge page size is requested explicitly, assume it is 2MB. This will
+		 * work fine when the actual size is less.  If it's more, we might get
+		 * mmap() or munmap() failures due to unaligned requests; but at this
+		 * writing, there are no reports of any non-Linux systems being picky
+		 * about that.
+		 */
+		*hugepagesize = 2 * 1024 * 1024;
+	}
+
+	*mmap_flags = MAP_HUGETLB;
+
+	/*
+	 * On recent enough Linux, also include the explicit page size, if
+	 * necessary.
+	 */
+#if defined(MAP_HUGE_MASK) && defined(MAP_HUGE_SHIFT)
+	if (*hugepagesize != default_hugepagesize)
+	{
+		int			shift = pg_ceil_log2_64(*hugepagesize);
+
+		*mmap_flags |= (shift & MAP_HUGE_MASK) << MAP_HUGE_SHIFT;
+	}
+#endif
 }
 
 #endif							/* MAP_HUGETLB */
@@ -583,7 +611,7 @@ CreateAnonymousSegment(Size *size)
 						 "(currently %zu bytes), reduce PostgreSQL's shared "
 						 "memory usage, perhaps by reducing shared_buffers or "
 						 "max_connections.",
-						 *size) : 0));
+						 allocsize) : 0));
 	}
 
 	*size = allocsize;