[v3,5/6] libgomp, nvptx: Cuda pinned memory

Message ID 20231211170405.2538247-6-ams@codesourcery.com
State New
Headers
Series libgomp: OpenMP pinned memory omp_alloc |

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Commit Message

Andrew Stubbs Dec. 11, 2023, 5:04 p.m. UTC
  Use Cuda to pin memory, instead of Linux mlock, when available.

There are two advantages: firstly, this gives a significant speed boost for
NVPTX offloading, and secondly, it side-steps the usual OS ulimit/rlimit
setting.

The design adds a device independent plugin API for allocating pinned memory,
and then implements it for NVPTX.  At present, the other supported devices do
not have equivalent capabilities (or requirements).

libgomp/ChangeLog:

	* config/linux/allocator.c: Include assert.h.
	(using_device_for_page_locked): New variable.
	(linux_memspace_alloc): Add init0 parameter. Support device pinning.
	(linux_memspace_calloc): Set init0 to true.
	(linux_memspace_free): Support device pinning.
	(linux_memspace_realloc): Support device pinning.
	(MEMSPACE_ALLOC): Set init0 to false.
	* libgomp-plugin.h
	(GOMP_OFFLOAD_page_locked_host_alloc): New prototype.
	(GOMP_OFFLOAD_page_locked_host_free): Likewise.
	* libgomp.h (gomp_page_locked_host_alloc): Likewise.
	(gomp_page_locked_host_free): Likewise.
	(struct gomp_device_descr): Add page_locked_host_alloc_func and
	page_locked_host_free_func.
	* libgomp.texi: Adjust the docs for the pinned trait.
	* libgomp_g.h (GOMP_enable_pinned_mode): New prototype.
	* plugin/plugin-nvptx.c
	(GOMP_OFFLOAD_page_locked_host_alloc): New function.
	(GOMP_OFFLOAD_page_locked_host_free): Likewise.
	* target.c (device_for_page_locked): New variable.
	(get_device_for_page_locked): New function.
	(gomp_page_locked_host_alloc): Likewise.
	(gomp_page_locked_host_free): Likewise.
	(gomp_load_plugin_for_device): Add page_locked_host_alloc and
	page_locked_host_free.
	* testsuite/libgomp.c/alloc-pinned-1.c: Change expectations for NVPTX
	devices.
	* testsuite/libgomp.c/alloc-pinned-2.c: Likewise.
	* testsuite/libgomp.c/alloc-pinned-3.c: Likewise.
	* testsuite/libgomp.c/alloc-pinned-4.c: Likewise.
	* testsuite/libgomp.c/alloc-pinned-5.c: Likewise.
	* testsuite/libgomp.c/alloc-pinned-6.c: Likewise.

Co-Authored-By: Thomas Schwinge <thomas@codesourcery.com>
---
 libgomp/config/linux/allocator.c             | 137 ++++++++++++++-----
 libgomp/libgomp-plugin.h                     |   2 +
 libgomp/libgomp.h                            |   4 +
 libgomp/libgomp.texi                         |  11 +-
 libgomp/libgomp_g.h                          |   1 +
 libgomp/plugin/plugin-nvptx.c                |  42 ++++++
 libgomp/target.c                             | 136 ++++++++++++++++++
 libgomp/testsuite/libgomp.c/alloc-pinned-1.c |  26 ++++
 libgomp/testsuite/libgomp.c/alloc-pinned-2.c |  26 ++++
 libgomp/testsuite/libgomp.c/alloc-pinned-3.c |  45 +++++-
 libgomp/testsuite/libgomp.c/alloc-pinned-4.c |  44 +++++-
 libgomp/testsuite/libgomp.c/alloc-pinned-5.c |  26 ++++
 libgomp/testsuite/libgomp.c/alloc-pinned-6.c |  35 ++++-
 13 files changed, 487 insertions(+), 48 deletions(-)
  

Comments

Tobias Burnus Dec. 12, 2023, 9:10 a.m. UTC | #1
On 11.12.23 18:04, Andrew Stubbs wrote:
> Use Cuda to pin memory, instead of Linux mlock, when available.
>
> There are two advantages: firstly, this gives a significant speed boost for
> NVPTX offloading, and secondly, it side-steps the usual OS ulimit/rlimit
> setting.
>
> The design adds a device independent plugin API for allocating pinned memory,
> and then implements it for NVPTX.  At present, the other supported devices do
> not have equivalent capabilities (or requirements).

LGTM. If you temporarily back out .texi's "@code{ompx_pinned_mem_alloc} 
allocator or" it can go in immediately after 1/6, i.e. before the 
ompx_pinned_mem_alloc patch.

As discussed in previous thread for the previous patch, I think the init 
should be done in the worker function of gomp_init_targets_once().

As discussed elsewhere, the patch can go in as is and I will provide a 
follow-up patch.

Thanks,

Tobias

> libgomp/ChangeLog:
>
> 	* config/linux/allocator.c: Include assert.h.
> 	(using_device_for_page_locked): New variable.
> 	(linux_memspace_alloc): Add init0 parameter. Support device pinning.
> 	(linux_memspace_calloc): Set init0 to true.
> 	(linux_memspace_free): Support device pinning.
> 	(linux_memspace_realloc): Support device pinning.
> 	(MEMSPACE_ALLOC): Set init0 to false.
> 	* libgomp-plugin.h
> 	(GOMP_OFFLOAD_page_locked_host_alloc): New prototype.
> 	(GOMP_OFFLOAD_page_locked_host_free): Likewise.
> 	* libgomp.h (gomp_page_locked_host_alloc): Likewise.
> 	(gomp_page_locked_host_free): Likewise.
> 	(struct gomp_device_descr): Add page_locked_host_alloc_func and
> 	page_locked_host_free_func.
> 	* libgomp.texi: Adjust the docs for the pinned trait.
> 	* libgomp_g.h (GOMP_enable_pinned_mode): New prototype.
> 	* plugin/plugin-nvptx.c
> 	(GOMP_OFFLOAD_page_locked_host_alloc): New function.
> 	(GOMP_OFFLOAD_page_locked_host_free): Likewise.
> 	* target.c (device_for_page_locked): New variable.
> 	(get_device_for_page_locked): New function.
> 	(gomp_page_locked_host_alloc): Likewise.
> 	(gomp_page_locked_host_free): Likewise.
> 	(gomp_load_plugin_for_device): Add page_locked_host_alloc and
> 	page_locked_host_free.
> 	* testsuite/libgomp.c/alloc-pinned-1.c: Change expectations for NVPTX
> 	devices.
> 	* testsuite/libgomp.c/alloc-pinned-2.c: Likewise.
> 	* testsuite/libgomp.c/alloc-pinned-3.c: Likewise.
> 	* testsuite/libgomp.c/alloc-pinned-4.c: Likewise.
> 	* testsuite/libgomp.c/alloc-pinned-5.c: Likewise.
> 	* testsuite/libgomp.c/alloc-pinned-6.c: Likewise.
>
> Co-Authored-By: Thomas Schwinge <thomas@codesourcery.com>
> ---
>   libgomp/config/linux/allocator.c             | 137 ++++++++++++++-----
>   libgomp/libgomp-plugin.h                     |   2 +
>   libgomp/libgomp.h                            |   4 +
>   libgomp/libgomp.texi                         |  11 +-
>   libgomp/libgomp_g.h                          |   1 +
>   libgomp/plugin/plugin-nvptx.c                |  42 ++++++
>   libgomp/target.c                             | 136 ++++++++++++++++++
>   libgomp/testsuite/libgomp.c/alloc-pinned-1.c |  26 ++++
>   libgomp/testsuite/libgomp.c/alloc-pinned-2.c |  26 ++++
>   libgomp/testsuite/libgomp.c/alloc-pinned-3.c |  45 +++++-
>   libgomp/testsuite/libgomp.c/alloc-pinned-4.c |  44 +++++-
>   libgomp/testsuite/libgomp.c/alloc-pinned-5.c |  26 ++++
>   libgomp/testsuite/libgomp.c/alloc-pinned-6.c |  35 ++++-
>   13 files changed, 487 insertions(+), 48 deletions(-)
>
  

Patch

diff --git a/libgomp/config/linux/allocator.c b/libgomp/config/linux/allocator.c
index 57278b1af91..8d681b5ec50 100644
--- a/libgomp/config/linux/allocator.c
+++ b/libgomp/config/linux/allocator.c
@@ -36,6 +36,11 @@ 
 
 /* Implement malloc routines that can handle pinned memory on Linux.
    
+   Given that pinned memory is typically used to help host <-> device memory
+   transfers, we attempt to allocate such memory using a device (really:
+   libgomp plugin), but fall back to mmap plus mlock if no suitable device is
+   available.
+
    It's possible to use mlock on any heap memory, but using munlock is
    problematic if there are multiple pinned allocations on the same page.
    Tracking all that manually would be possible, but adds overhead. This may
@@ -49,6 +54,7 @@ 
 #define _GNU_SOURCE
 #include <sys/mman.h>
 #include <string.h>
+#include <assert.h>
 #include "libgomp.h"
 
 static bool always_pinned_mode = false;
@@ -65,45 +71,87 @@  GOMP_enable_pinned_mode ()
     always_pinned_mode = true;
 }
 
+static int using_device_for_page_locked
+  = /* uninitialized */ -1;
+
 static void *
-linux_memspace_alloc (omp_memspace_handle_t memspace, size_t size, int pin)
+linux_memspace_alloc (omp_memspace_handle_t memspace, size_t size, int pin,
+		      bool init0)
 {
-  (void)memspace;
+  gomp_debug (0, "%s: memspace=%llu, size=%llu, pin=%d, init0=%d\n",
+	      __FUNCTION__, (unsigned long long) memspace,
+	      (unsigned long long) size, pin, init0);
+
+  void *addr;
 
   /* Explicit pinning may not be required.  */
   pin = pin && !always_pinned_mode;
 
   if (pin)
     {
-      /* Note that mmap always returns zeroed memory and is therefore also a
-	 suitable implementation of calloc.  */
-      void *addr = mmap (NULL, size, PROT_READ | PROT_WRITE,
-			 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
-      if (addr == MAP_FAILED)
-	return NULL;
-
-      if (mlock (addr, size))
+      int using_device
+	= __atomic_load_n (&using_device_for_page_locked,
+			   MEMMODEL_RELAXED);
+      gomp_debug (0, "  using_device=%d\n",
+		  using_device);
+      if (using_device != 0)
 	{
-	  gomp_debug (0, "libgomp: failed to pin %ld bytes of"
-		      " memory (ulimit too low?)\n", size);
-	  munmap (addr, size);
-	  return NULL;
+	  using_device = gomp_page_locked_host_alloc (&addr, size);
+	  int using_device_old
+	    = __atomic_exchange_n (&using_device_for_page_locked,
+				   using_device, MEMMODEL_RELAXED);
+	  gomp_debug (0, "  using_device=%d, using_device_old=%d\n",
+		      using_device, using_device_old);
+	  assert (using_device_old == -1
+		  /* We shouldn't have concurrently changed our mind.  */
+		  || using_device_old == using_device);
+	}
+      if (using_device == 0)
+	{
+	  gomp_debug (0, "  mmap\n");
+	  addr = mmap (NULL, size, PROT_READ | PROT_WRITE,
+		       MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	  if (addr == MAP_FAILED)
+	    addr = NULL;
+	  else
+	    {
+	      /* 'mmap' zero-initializes.  */
+	      init0 = false;
+
+	      gomp_debug (0, "  mlock\n");
+	      if (mlock (addr, size))
+		{
+		  gomp_debug (0, "libgomp: failed to pin %ld bytes of"
+			      " memory (ulimit too low?)\n", size);
+		  munmap (addr, size);
+		  addr = NULL;
+		}
+	    }
 	}
-
-      return addr;
     }
   else
-    return malloc (size);
+    addr = malloc (size);
+
+  if (addr && init0)
+    {
+      gomp_debug (0, "  init0\n");
+      memset (addr, 0, size);
+    }
+
+  return addr;
 }
 
 static void *
 linux_memspace_calloc (omp_memspace_handle_t memspace, size_t size, int pin)
 {
+  gomp_debug (0, "%s: memspace=%llu, size=%llu, pin=%d\n",
+	      __FUNCTION__, (unsigned long long) memspace, (unsigned long long) size, pin);
+
   /* Explicit pinning may not be required.  */
   pin = pin && !always_pinned_mode;
 
   if (pin)
-    return linux_memspace_alloc (memspace, size, pin);
+    return linux_memspace_alloc (memspace, size, pin, true);
   else
     return calloc (1, size);
 }
@@ -112,13 +160,25 @@  static void
 linux_memspace_free (omp_memspace_handle_t memspace, void *addr, size_t size,
 		     int pin)
 {
-  (void)memspace;
+  gomp_debug (0, "%s: memspace=%llu, addr=%p, size=%llu, pin=%d\n",
+	      __FUNCTION__, (unsigned long long) memspace, addr, (unsigned long long) size, pin);
 
   /* Explicit pinning may not be required.  */
   pin = pin && !always_pinned_mode;
 
   if (pin)
-    munmap (addr, size);
+    {
+      int using_device
+	= __atomic_load_n (&using_device_for_page_locked,
+			   MEMMODEL_RELAXED);
+      gomp_debug (0, "  using_device=%d\n",
+		  using_device);
+      if (using_device == 1)
+	gomp_page_locked_host_free (addr);
+      else
+	/* 'munlock'ing is implicit with following 'munmap'.  */
+	munmap (addr, size);
+    }
   else
     free (addr);
 }
@@ -127,11 +187,25 @@  static void *
 linux_memspace_realloc (omp_memspace_handle_t memspace, void *addr,
 			size_t oldsize, size_t size, int oldpin, int pin)
 {
+  gomp_debug (0, "%s: memspace=%llu, addr=%p, oldsize=%llu, size=%llu, oldpin=%d, pin=%d\n",
+	      __FUNCTION__, (unsigned long long) memspace, addr, (unsigned long long) oldsize, (unsigned long long) size, oldpin, pin);
+
   /* Explicit pinning may not be required.  */
   pin = pin && !always_pinned_mode;
 
   if (oldpin && pin)
     {
+      /* We can only expect to be able to just 'mremap' if not using a device
+	 for page-locked memory.  */
+      int using_device
+	= __atomic_load_n (&using_device_for_page_locked,
+		       MEMMODEL_RELAXED);
+      gomp_debug (0, "  using_device=%d\n",
+		  using_device);
+      if (using_device != 0)
+	goto manual_realloc;
+
+      gomp_debug (0, "  mremap\n");
       void *newaddr = mremap (addr, oldsize, size, MREMAP_MAYMOVE);
       if (newaddr == MAP_FAILED)
 	return NULL;
@@ -139,18 +213,19 @@  linux_memspace_realloc (omp_memspace_handle_t memspace, void *addr,
       return newaddr;
     }
   else if (oldpin || pin)
-    {
-      void *newaddr = linux_memspace_alloc (memspace, size, pin);
-      if (newaddr)
-	{
-	  memcpy (newaddr, addr, oldsize < size ? oldsize : size);
-	  linux_memspace_free (memspace, addr, oldsize, oldpin);
-	}
-
-      return newaddr;
-    }
+    goto manual_realloc;
   else
     return realloc (addr, size);
+
+manual_realloc:;
+  void *newaddr = linux_memspace_alloc (memspace, size, pin, false);
+  if (newaddr)
+    {
+      memcpy (newaddr, addr, oldsize < size ? oldsize : size);
+      linux_memspace_free (memspace, addr, oldsize, oldpin);
+    }
+
+  return newaddr;
 }
 
 static int
@@ -161,7 +236,7 @@  linux_memspace_validate (omp_memspace_handle_t, unsigned, int)
 }
 
 #define MEMSPACE_ALLOC(MEMSPACE, SIZE, PIN) \
-  linux_memspace_alloc (MEMSPACE, SIZE, PIN)
+  linux_memspace_alloc (MEMSPACE, SIZE, PIN, false)
 #define MEMSPACE_CALLOC(MEMSPACE, SIZE, PIN) \
   linux_memspace_calloc (MEMSPACE, SIZE, PIN)
 #define MEMSPACE_REALLOC(MEMSPACE, ADDR, OLDSIZE, SIZE, OLDPIN, PIN) \
diff --git a/libgomp/libgomp-plugin.h b/libgomp/libgomp-plugin.h
index 3ce032c5cc0..319818de121 100644
--- a/libgomp/libgomp-plugin.h
+++ b/libgomp/libgomp-plugin.h
@@ -139,6 +139,8 @@  extern int GOMP_OFFLOAD_load_image (int, unsigned, const void *,
 extern bool GOMP_OFFLOAD_unload_image (int, unsigned, const void *);
 extern void *GOMP_OFFLOAD_alloc (int, size_t);
 extern bool GOMP_OFFLOAD_free (int, void *);
+extern bool GOMP_OFFLOAD_page_locked_host_alloc (void **, size_t);
+extern bool GOMP_OFFLOAD_page_locked_host_free (void *);
 extern bool GOMP_OFFLOAD_dev2host (int, void *, const void *, size_t);
 extern bool GOMP_OFFLOAD_host2dev (int, void *, const void *, size_t);
 extern bool GOMP_OFFLOAD_dev2dev (int, void *, const void *, size_t);
diff --git a/libgomp/libgomp.h b/libgomp/libgomp.h
index fa29f428976..8c9e50d88fd 100644
--- a/libgomp/libgomp.h
+++ b/libgomp/libgomp.h
@@ -1128,6 +1128,8 @@  extern int gomp_get_num_devices (void);
 extern bool gomp_target_task_fn (void *);
 extern void gomp_target_rev (uint64_t, uint64_t, uint64_t, uint64_t, uint64_t,
 			     int, struct goacc_asyncqueue *);
+extern bool gomp_page_locked_host_alloc (void **, size_t);
+extern void gomp_page_locked_host_free (void *);
 
 /* Splay tree definitions.  */
 typedef struct splay_tree_node_s *splay_tree_node;
@@ -1406,6 +1408,8 @@  struct gomp_device_descr
   __typeof (GOMP_OFFLOAD_unload_image) *unload_image_func;
   __typeof (GOMP_OFFLOAD_alloc) *alloc_func;
   __typeof (GOMP_OFFLOAD_free) *free_func;
+  __typeof (GOMP_OFFLOAD_page_locked_host_alloc) *page_locked_host_alloc_func;
+  __typeof (GOMP_OFFLOAD_page_locked_host_free) *page_locked_host_free_func;
   __typeof (GOMP_OFFLOAD_dev2host) *dev2host_func;
   __typeof (GOMP_OFFLOAD_host2dev) *host2dev_func;
   __typeof (GOMP_OFFLOAD_memcpy2d) *memcpy2d_func;
diff --git a/libgomp/libgomp.texi b/libgomp/libgomp.texi
index 1f73c49c9b8..a3a49d59409 100644
--- a/libgomp/libgomp.texi
+++ b/libgomp/libgomp.texi
@@ -5756,8 +5756,9 @@  a @code{nearest} allocation.
 
 Additional notes regarding the traits:
 @itemize
-@item The @code{pinned} trait is supported on Linux hosts, but is subject to
-      the OS @code{ulimit}/@code{rlimit} locked memory settings.
+@item The @code{pinned} trait is supported on Linux hosts, but is usually
+      subject to the OS @code{ulimit}/@code{rlimit} locked memory settings (see
+      @ref{Offload-Target Specifics} for exceptions).
 @item The default for the @code{pool_size} trait is no pool and for every
       (re)allocation the associated library routine is called, which might
       internally use a memory pool.
@@ -5937,6 +5938,12 @@  The implementation remark:
       @code{omp_thread_mem_alloc}, all use low-latency memory as first
       preference, and fall back to main graphics memory when the low-latency
       pool is exhausted.
+@item Pinned memory allocated using @code{omp_alloc} with the
+      @code{ompx_pinned_mem_alloc} allocator or the @code{pinned} trait is
+      obtained via the CUDA API when an NVPTX device is present.  This provides
+      a performance boost for NVPTX offload code and also allows unlimited use
+      of pinned memory regardless of the OS @code{ulimit}/@code{rlimit}
+      settings.
 @end itemize
 
 
diff --git a/libgomp/libgomp_g.h b/libgomp/libgomp_g.h
index 95046312ae9..1773f500c94 100644
--- a/libgomp/libgomp_g.h
+++ b/libgomp/libgomp_g.h
@@ -368,6 +368,7 @@  extern void GOMP_teams_reg (void (*) (void *), void *, unsigned, unsigned,
 
 extern void *GOMP_alloc (size_t, size_t, uintptr_t);
 extern void GOMP_free (void *, uintptr_t);
+extern void GOMP_enable_pinned_mode (void);
 
 /* error.c */
 
diff --git a/libgomp/plugin/plugin-nvptx.c b/libgomp/plugin/plugin-nvptx.c
index d4a254ed4f0..3fb6650a393 100644
--- a/libgomp/plugin/plugin-nvptx.c
+++ b/libgomp/plugin/plugin-nvptx.c
@@ -1608,6 +1608,48 @@  GOMP_OFFLOAD_free (int ord, void *ptr)
 	  && nvptx_free (ptr, ptx_devices[ord]));
 }
 
+bool
+GOMP_OFFLOAD_page_locked_host_alloc (void **ptr, size_t size)
+{
+  GOMP_PLUGIN_debug (0, "nvptx %s: ptr=%p, size=%llu\n",
+		     __FUNCTION__, ptr, (unsigned long long) size);
+
+  if (size == 0)
+    {
+      /* Special case to ensure omp_alloc specification compliance.  */
+      *ptr = NULL;
+      GOMP_PLUGIN_debug (0, "  -> *ptr=null\n");
+      return true;
+    }
+
+  CUresult r;
+
+  unsigned int flags = 0;
+  /* Given 'CU_DEVICE_ATTRIBUTE_UNIFIED_ADDRESSING', we don't need
+     'flags |= CU_MEMHOSTALLOC_PORTABLE;' here.  */
+  r = CUDA_CALL_NOCHECK (cuMemHostAlloc, ptr, size, flags);
+  if (r == CUDA_ERROR_OUT_OF_MEMORY)
+    *ptr = NULL;
+  else if (r != CUDA_SUCCESS)
+    {
+      GOMP_PLUGIN_error ("cuMemHostAlloc error: %s", cuda_error (r));
+      return false;
+    }
+  GOMP_PLUGIN_debug (0, "  -> *ptr=%p\n",
+		     *ptr);
+  return true;
+}
+
+bool
+GOMP_OFFLOAD_page_locked_host_free (void *ptr)
+{
+  GOMP_PLUGIN_debug (0, "nvptx %s: ptr=%p\n",
+		     __FUNCTION__, ptr);
+
+  CUDA_CALL (cuMemFreeHost, ptr);
+  return true;
+}
+
 void
 GOMP_OFFLOAD_openacc_exec (void (*fn) (void *),
 			   size_t mapnum  __attribute__((unused)),
diff --git a/libgomp/target.c b/libgomp/target.c
index f30c20255d3..d7c9ab780aa 100644
--- a/libgomp/target.c
+++ b/libgomp/target.c
@@ -4345,6 +4345,140 @@  omp_target_free (void *device_ptr, int device_num)
   gomp_mutex_unlock (&devicep->lock);
 }
 
+/* Device (really: libgomp plugin) to use for paged-locked memory.  We
+   assume there is either none or exactly one such device for the lifetime of
+   the process.  */
+
+static struct gomp_device_descr *device_for_page_locked
+  = /* uninitialized */ (void *) -1;
+
+static struct gomp_device_descr *
+get_device_for_page_locked (void)
+{
+  gomp_debug (0, "%s\n",
+	      __FUNCTION__);
+
+  struct gomp_device_descr *device;
+#ifdef HAVE_SYNC_BUILTINS
+  device
+    = __atomic_load_n (&device_for_page_locked, MEMMODEL_RELAXED);
+  if (device == (void *) -1)
+    {
+      gomp_debug (0, "  init\n");
+
+      gomp_init_targets_once ();
+
+      device = NULL;
+      for (int i = 0; i < num_devices; ++i)
+	{
+	  gomp_debug (0, "  i=%d, target_id=%d\n",
+		      i, devices[i].target_id);
+
+	  /* We consider only the first device of potentially several of the
+	     same type as this functionality is not specific to an individual
+	     offloading device, but instead relates to the host-side
+	     implementation of the respective offloading implementation.  */
+	  if (devices[i].target_id != 0)
+	    continue;
+
+	  if (!devices[i].page_locked_host_alloc_func)
+	    continue;
+
+	  gomp_debug (0, "  found device: %p (%s)\n",
+		      &devices[i], devices[i].name);
+	  if (device)
+	    gomp_fatal ("Unclear how %s and %s libgomp plugins may"
+			" simultaneously provide functionality"
+			" for page-locked memory",
+			device->name, devices[i].name);
+	  else
+	    device = &devices[i];
+	}
+
+      struct gomp_device_descr *device_old
+	= __atomic_exchange_n (&device_for_page_locked, device,
+			       MEMMODEL_RELAXED);
+      gomp_debug (0, "  old device_for_page_locked: %p\n",
+		  device_old);
+      assert (device_old == (void *) -1
+	      /* We shouldn't have concurrently found a different or no
+		 device.  */
+	      || device_old == device);
+    }
+#else /* !HAVE_SYNC_BUILTINS */
+  gomp_debug (0, "  not implemented for '!HAVE_SYNC_BUILTINS'\n");
+  (void) &device_for_page_locked;
+  device = NULL;
+#endif /* HAVE_SYNC_BUILTINS */
+
+  gomp_debug (0, "  -> device=%p (%s)\n",
+	      device, device ? device->name : "[none]");
+  return device;
+}
+
+/* Allocate page-locked host memory.
+   Returns whether we have a device capable of that.  */
+
+attribute_hidden bool
+gomp_page_locked_host_alloc (void **ptr, size_t size)
+{
+  gomp_debug (0, "%s: ptr=%p, size=%llu\n",
+	      __FUNCTION__, ptr, (unsigned long long) size);
+
+  struct gomp_device_descr *device = get_device_for_page_locked ();
+  gomp_debug (0, "  device=%p (%s)\n",
+	      device, device ? device->name : "[none]");
+  if (device)
+    {
+      gomp_mutex_lock (&device->lock);
+      if (device->state == GOMP_DEVICE_UNINITIALIZED)
+	gomp_init_device (device);
+      else if (device->state == GOMP_DEVICE_FINALIZED)
+	{
+	  gomp_mutex_unlock (&device->lock);
+	  gomp_fatal ("Device %s used for for page-locked memory is finalized",
+		      device->name);
+	}
+      gomp_mutex_unlock (&device->lock);
+
+      if (!device->page_locked_host_alloc_func (ptr, size))
+	gomp_fatal ("Failed to allocate page-locked host memory"
+		    " via %s libgomp plugin",
+		    device->name);
+    }
+  return device != NULL;
+}
+
+/* Free page-locked host memory.
+   This must only be called if 'gomp_page_locked_host_alloc' returned
+   'true'.  */
+
+attribute_hidden void
+gomp_page_locked_host_free (void *ptr)
+{
+  gomp_debug (0, "%s: ptr=%p\n",
+	      __FUNCTION__, ptr);
+
+  struct gomp_device_descr *device = get_device_for_page_locked ();
+  gomp_debug (0, "  device=%p (%s)\n",
+	      device, device ? device->name : "[none]");
+  assert (device);
+
+  gomp_mutex_lock (&device->lock);
+  assert (device->state != GOMP_DEVICE_UNINITIALIZED);
+  if (device->state == GOMP_DEVICE_FINALIZED)
+    {
+      gomp_mutex_unlock (&device->lock);
+      return;
+    }
+  gomp_mutex_unlock (&device->lock);
+
+  if (!device->page_locked_host_free_func (ptr))
+    gomp_fatal ("Failed to free page-locked host memory"
+		" via %s libgomp plugin",
+		device->name);
+}
+
 int
 omp_target_is_present (const void *ptr, int device_num)
 {
@@ -5067,6 +5201,8 @@  gomp_load_plugin_for_device (struct gomp_device_descr *device,
   DLSYM (unload_image);
   DLSYM (alloc);
   DLSYM (free);
+  DLSYM_OPT (page_locked_host_alloc, page_locked_host_alloc);
+  DLSYM_OPT (page_locked_host_free, page_locked_host_free);
   DLSYM (dev2host);
   DLSYM (host2dev);
   DLSYM_OPT (memcpy2d, memcpy2d);
diff --git a/libgomp/testsuite/libgomp.c/alloc-pinned-1.c b/libgomp/testsuite/libgomp.c/alloc-pinned-1.c
index e17a21f0a6c..2da660b17ec 100644
--- a/libgomp/testsuite/libgomp.c/alloc-pinned-1.c
+++ b/libgomp/testsuite/libgomp.c/alloc-pinned-1.c
@@ -2,6 +2,8 @@ 
 
 /* { dg-xfail-run-if "Pinning not implemented on this host" { ! *-*-linux-gnu } } */
 
+/* { dg-additional-options -DOFFLOAD_DEVICE_NVPTX { target offload_device_nvptx } } */
+
 /* Test that pinned memory works.  */
 
 #include <stdio.h>
@@ -68,10 +70,16 @@  verify0 (char *p, size_t s)
 int
 main ()
 {
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* Go big or go home.
+     The OS ulimit does not affect memory locked via CUDA for NVPTX devices. */
+  const int SIZE = 40 * 1024 * 1024;
+#else
   /* Allocate at least a page each time, allowing space for overhead,
      but stay within the ulimit.  */
   const int SIZE = PAGE_SIZE - 128;
   CHECK_SIZE (SIZE * 5);  // This is intended to help diagnose failures
+#endif
 
   const omp_alloctrait_t traits[] = {
       { omp_atk_pinned, 1 }
@@ -93,21 +101,39 @@  main ()
     abort ();
 
   int amount = get_pinned_mem ();
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* This doesn't show up as process 'VmLck'ed memory.  */
+  if (amount != 0)
+    abort ();
+#else
   if (amount == 0)
     abort ();
+#endif
 
   p = omp_realloc (p, SIZE * 2, allocator, allocator);
 
   int amount2 = get_pinned_mem ();
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* This doesn't show up as process 'VmLck'ed memory.  */
+  if (amount2 != 0)
+    abort ();
+#else
   if (amount2 <= amount)
     abort ();
+#endif
 
   /* SIZE*2 ensures that it doesn't slot into the space possibly
      vacated by realloc.  */
   p = omp_calloc (1, SIZE * 2, allocator);
 
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* This doesn't show up as process 'VmLck'ed memory.  */
+  if (get_pinned_mem () != 0)
+    abort ();
+#else
   if (get_pinned_mem () <= amount2)
     abort ();
+#endif
 
   verify0 (p, SIZE * 2);
 
diff --git a/libgomp/testsuite/libgomp.c/alloc-pinned-2.c b/libgomp/testsuite/libgomp.c/alloc-pinned-2.c
index 3cf322cfbc8..5dd765d24c5 100644
--- a/libgomp/testsuite/libgomp.c/alloc-pinned-2.c
+++ b/libgomp/testsuite/libgomp.c/alloc-pinned-2.c
@@ -2,6 +2,8 @@ 
 
 /* { dg-xfail-run-if "Pinning not implemented on this host" { ! *-*-linux-gnu } } */
 
+/* { dg-additional-options -DOFFLOAD_DEVICE_NVPTX { target offload_device_nvptx } } */
+
 /* Test that pinned memory works (pool_size code path).  */
 
 #include <stdio.h>
@@ -68,10 +70,16 @@  verify0 (char *p, size_t s)
 int
 main ()
 {
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* Go big or go home.
+     The OS ulimit does not affect memory locked via CUDA for NVPTX devices. */
+  const int SIZE = 40 * 1024 * 1024;
+#else
   /* Allocate at least a page each time, allowing space for overhead,
      but stay within the ulimit.  */
   const int SIZE = PAGE_SIZE - 128;
   CHECK_SIZE (SIZE * 5);  // This is intended to help diagnose failures
+#endif
 
   const omp_alloctrait_t traits[] = {
       { omp_atk_pinned, 1 },
@@ -94,16 +102,28 @@  main ()
     abort ();
 
   int amount = get_pinned_mem ();
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* This doesn't show up as process 'VmLck'ed memory.  */
+  if (amount != 0)
+    abort ();
+#else
   if (amount == 0)
     abort ();
+#endif
 
   p = omp_realloc (p, SIZE * 2, allocator, allocator);
   if (!p)
     abort ();
 
   int amount2 = get_pinned_mem ();
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* This doesn't show up as process 'VmLck'ed memory.  */
+  if (amount2 != 0)
+    abort ();
+#else
   if (amount2 <= amount)
     abort ();
+#endif
 
   /* SIZE*2 ensures that it doesn't slot into the space possibly
      vacated by realloc.  */
@@ -111,8 +131,14 @@  main ()
   if (!p)
     abort ();
 
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* This doesn't show up as process 'VmLck'ed memory.  */
+  if (get_pinned_mem () != 0)
+    abort ();
+#else
   if (get_pinned_mem () <= amount2)
     abort ();
+#endif
 
   verify0 (p, SIZE * 2);
 
diff --git a/libgomp/testsuite/libgomp.c/alloc-pinned-3.c b/libgomp/testsuite/libgomp.c/alloc-pinned-3.c
index 53e4720cc9c..b17daf7e222 100644
--- a/libgomp/testsuite/libgomp.c/alloc-pinned-3.c
+++ b/libgomp/testsuite/libgomp.c/alloc-pinned-3.c
@@ -1,5 +1,7 @@ 
 /* { dg-do run } */
 
+/* { dg-additional-options -DOFFLOAD_DEVICE_NVPTX { target offload_device_nvptx } } */
+
 /* Test that pinned memory fails correctly.  */
 
 #include <stdio.h>
@@ -75,8 +77,15 @@  verify0 (char *p, size_t s)
 int
 main ()
 {
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* Go big or go home.
+     The OS ulimit does not affect memory locked via CUDA for NVPTX devices. */
+  const int SIZE = 40 * 1024 * 1024;
+#else
   /* This needs to be large enough to cover multiple pages.  */
   const int SIZE = PAGE_SIZE * 4;
+#endif
+  const int PIN_LIMIT = PAGE_SIZE * 2;
 
   /* Pinned memory, no fallback.  */
   const omp_alloctrait_t traits1[] = {
@@ -101,23 +110,34 @@  main ()
 #endif
 
   /* Ensure that the limit is smaller than the allocation.  */
-  set_pin_limit (SIZE / 2);
+  set_pin_limit (PIN_LIMIT);
 
   // Sanity check
   if (get_pinned_mem () != 0)
     abort ();
 
-  // Should fail
   void *p1 = omp_alloc (SIZE, allocator1);
+#ifdef OFFLOAD_DEVICE_NVPTX
+  // Doesn't care about 'set_pin_limit'.
+  if (!p1)
+    abort ();
+#else
+  // Should fail
   if (p1)
     abort ();
+#endif
 
-  // Should fail
   void *p2 = omp_calloc (1, SIZE, allocator1);
+#ifdef OFFLOAD_DEVICE_NVPTX
+  // Doesn't care about 'set_pin_limit'.
+  if (!p2)
+    abort ();
+#else
+  // Should fail
   if (p2)
     abort ();
+#endif
 
-  // Should fall back
   void *p3 = omp_alloc (SIZE, allocator2);
   if (!p3)
     abort ();
@@ -128,16 +148,29 @@  main ()
     abort ();
   verify0 (p4, SIZE);
 
-  // Should fail to realloc
   void *notpinned = omp_alloc (SIZE, omp_default_mem_alloc);
   void *p5 = omp_realloc (notpinned, SIZE, allocator1, omp_default_mem_alloc);
+#ifdef OFFLOAD_DEVICE_NVPTX
+  // Doesn't care about 'set_pin_limit'; does reallocate.
+  if (!notpinned || !p5 || p5 == notpinned)
+    abort ();
+#else
+  // Should fail to realloc
   if (!notpinned || p5)
     abort ();
+#endif
 
-  // Should fall back to no realloc needed
+#ifdef OFFLOAD_DEVICE_NVPTX
+  void *p6 = omp_realloc (p5, SIZE, allocator2, allocator1);
+  // Does reallocate.
+  if (p5 == p6)
+    abort ();
+#else
   void *p6 = omp_realloc (notpinned, SIZE, allocator2, omp_default_mem_alloc);
+  // Should fall back to no realloc needed
   if (p6 != notpinned)
     abort ();
+#endif
 
   // No memory should have been pinned
   int amount = get_pinned_mem ();
diff --git a/libgomp/testsuite/libgomp.c/alloc-pinned-4.c b/libgomp/testsuite/libgomp.c/alloc-pinned-4.c
index 9d850c23e4b..aadd9249ba9 100644
--- a/libgomp/testsuite/libgomp.c/alloc-pinned-4.c
+++ b/libgomp/testsuite/libgomp.c/alloc-pinned-4.c
@@ -1,5 +1,7 @@ 
 /* { dg-do run } */
 
+/* { dg-additional-options -DOFFLOAD_DEVICE_NVPTX { target offload_device_nvptx } } */
+
 /* Test that pinned memory fails correctly, pool_size code path.  */
 
 #include <stdio.h>
@@ -75,8 +77,15 @@  verify0 (char *p, size_t s)
 int
 main ()
 {
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* Go big or go home.
+     The OS ulimit does not affect memory locked via CUDA for NVPTX devices. */
+  const int SIZE = 40 * 1024 * 1024;
+#else
   /* This needs to be large enough to cover multiple pages.  */
   const int SIZE = PAGE_SIZE * 4;
+#endif
+  const int PIN_LIMIT = PAGE_SIZE * 2;
 
   /* Pinned memory, no fallback.  */
   const omp_alloctrait_t traits1[] = {
@@ -103,21 +112,33 @@  main ()
 #endif
 
   /* Ensure that the limit is smaller than the allocation.  */
-  set_pin_limit (SIZE / 2);
+  set_pin_limit (PIN_LIMIT);
 
   // Sanity check
   if (get_pinned_mem () != 0)
     abort ();
 
-  // Should fail
   void *p = omp_alloc (SIZE, allocator1);
+#ifdef OFFLOAD_DEVICE_NVPTX
+  // Doesn't care about 'set_pin_limit'.
+  if (!p)
+    abort ();
+#else
+  // Should fail
   if (p)
     abort ();
+#endif
 
-  // Should fail
   p = omp_calloc (1, SIZE, allocator1);
+#ifdef OFFLOAD_DEVICE_NVPTX
+  // Doesn't care about 'set_pin_limit'.
+  if (!p)
+    abort ();
+#else
+  // Should fail
   if (p)
     abort ();
+#endif
 
   // Should fall back
   p = omp_alloc (SIZE, allocator2);
@@ -130,16 +151,29 @@  main ()
     abort ();
   verify0 (p, SIZE);
 
-  // Should fail to realloc
   void *notpinned = omp_alloc (SIZE, omp_default_mem_alloc);
   p = omp_realloc (notpinned, SIZE, allocator1, omp_default_mem_alloc);
+#ifdef OFFLOAD_DEVICE_NVPTX
+  // Doesn't care about 'set_pin_limit'; does reallocate.
+  if (!notpinned || !p || p == notpinned)
+    abort ();
+#else
+  // Should fail to realloc
   if (!notpinned || p)
     abort ();
+#endif
 
-  // Should fall back to no realloc needed
+#ifdef OFFLOAD_DEVICE_NVPTX
+  void *p_ = omp_realloc (p, SIZE, allocator2, allocator1);
+  // Does reallocate.
+  if (p_ == p)
+    abort ();
+#else
   p = omp_realloc (notpinned, SIZE, allocator2, omp_default_mem_alloc);
+  // Should fall back to no realloc needed
   if (p != notpinned)
     abort ();
+#endif
 
   // No memory should have been pinned
   int amount = get_pinned_mem ();
diff --git a/libgomp/testsuite/libgomp.c/alloc-pinned-5.c b/libgomp/testsuite/libgomp.c/alloc-pinned-5.c
index 18e6d20ca5b..95e4562537c 100644
--- a/libgomp/testsuite/libgomp.c/alloc-pinned-5.c
+++ b/libgomp/testsuite/libgomp.c/alloc-pinned-5.c
@@ -2,6 +2,8 @@ 
 
 /* { dg-xfail-run-if "Pinning not implemented on this host" { ! *-*-linux-gnu } } */
 
+/* { dg-additional-options -DOFFLOAD_DEVICE_NVPTX { target offload_device_nvptx } } */
+
 /* Test that ompx_pinned_mem_alloc works.  */
 
 #include <stdio.h>
@@ -67,10 +69,16 @@  verify0 (char *p, size_t s)
 int
 main ()
 {
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* Go big or go home.
+     The OS ulimit does not affect memory locked via CUDA for NVPTX devices. */
+  const int SIZE = 40 * 1024 * 1024;
+#else
   /* Allocate at least a page each time, allowing space for overhead,
      but stay within the ulimit.  */
   const int SIZE = PAGE_SIZE - 128;
   CHECK_SIZE (SIZE * 5);
+#endif
 
   // Sanity check
   if (get_pinned_mem () != 0)
@@ -81,21 +89,39 @@  main ()
     abort ();
 
   int amount = get_pinned_mem ();
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* This doesn't show up as process 'VmLck'ed memory.  */
+  if (amount != 0)
+    abort ();
+#else
   if (amount == 0)
     abort ();
+#endif
 
   p = omp_realloc (p, SIZE * 2, ompx_pinned_mem_alloc, ompx_pinned_mem_alloc);
 
   int amount2 = get_pinned_mem ();
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* This doesn't show up as process 'VmLck'ed memory.  */
+  if (amount2 != 0)
+    abort ();
+#else
   if (amount2 <= amount)
     abort ();
+#endif
 
   /* SIZE*2 ensures that it doesn't slot into the space possibly
      vacated by realloc.  */
   p = omp_calloc (1, SIZE * 2, ompx_pinned_mem_alloc);
 
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* This doesn't show up as process 'VmLck'ed memory.  */
+  if (get_pinned_mem () != 0)
+    abort ();
+#else
   if (get_pinned_mem () <= amount2)
     abort ();
+#endif
 
   verify0 (p, SIZE * 2);
 
diff --git a/libgomp/testsuite/libgomp.c/alloc-pinned-6.c b/libgomp/testsuite/libgomp.c/alloc-pinned-6.c
index f80a0264f97..aefb69a1d60 100644
--- a/libgomp/testsuite/libgomp.c/alloc-pinned-6.c
+++ b/libgomp/testsuite/libgomp.c/alloc-pinned-6.c
@@ -1,5 +1,7 @@ 
 /* { dg-do run } */
 
+/* { dg-additional-options -DOFFLOAD_DEVICE_NVPTX { target offload_device_nvptx } } */
+
 /* Test that ompx_pinned_mem_alloc fails correctly.  */
 
 #include <stdio.h>
@@ -66,31 +68,56 @@  set_pin_limit ()
 int
 main ()
 {
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* Go big or go home.
+     The OS ulimit does not affect memory locked via CUDA for NVPTX devices. */
+  const int SIZE = 40 * 1024 * 1024;
+#else
   /* Allocate at least a page each time, but stay within the ulimit.  */
   const int SIZE = PAGE_SIZE * 4;
+#endif
+  const int PIN_LIMIT = PAGE_SIZE*2;
 
   /* Ensure that the limit is smaller than the allocation.  */
-  set_pin_limit (SIZE / 2);
+  set_pin_limit (PIN_LIMIT);
 
   // Sanity check
   if (get_pinned_mem () != 0)
     abort ();
 
-  // Should fail
   void *p = omp_alloc (SIZE, ompx_pinned_mem_alloc);
+#ifdef OFFLOAD_DEVICE_NVPTX
+  // Doesn't care about 'set_pin_limit'.
+  if (!p)
+    abort ();
+#else
+  // Should fail
   if (p)
     abort ();
+#endif
 
-  // Should fail
   p = omp_calloc (1, SIZE, ompx_pinned_mem_alloc);
+#ifdef OFFLOAD_DEVICE_NVPTX
+  // Doesn't care about 'set_pin_limit'.
+  if (!p)
+    abort ();
+#else
+  // Should fail
   if (p)
     abort ();
+#endif
 
-  // Should fail to realloc
   void *notpinned = omp_alloc (SIZE, omp_default_mem_alloc);
   p = omp_realloc (notpinned, SIZE, ompx_pinned_mem_alloc, omp_default_mem_alloc);
+#ifdef OFFLOAD_DEVICE_NVPTX
+  // Doesn't care about 'set_pin_limit'; does reallocate.
+  if (!notpinned || !p || p == notpinned)
+    abort ();
+#else
+  // Should fail to realloc
   if (!notpinned || p)
     abort ();
+#endif
 
   // No memory should have been pinned
   int amount = get_pinned_mem ();