diff mbox series

[og12] Attempt to register OpenMP pinned memory using a device instead of 'mlock' (was: [PATCH] libgomp, openmp: pinned memory)

Message ID 87lekxxo23.fsf@euler.schwinge.homeip.net
State New
Headers show
Series [og12] Attempt to register OpenMP pinned memory using a device instead of 'mlock' (was: [PATCH] libgomp, openmp: pinned memory) | expand

Commit Message

Thomas Schwinge Feb. 16, 2023, 10:06 p.m. UTC
Hi!

On 2023-02-16T16:17:32+0000, "Stubbs, Andrew via Gcc-patches" <gcc-patches@gcc.gnu.org> wrote:
>> On 2022-06-09T11:38:22+0200, I wrote:
>> > [...]
>> > *register* your standard 'malloc'ed etc. memory via 'cuMemHostRegister',
>> > <https://docs.nvidia.com/cuda/cuda-driver-api/group__CUDA__MEM.html#group__CUDA__MEM_1gf0a9fe11544326dabd743b7aa6b54223>:
>> > "Page-locks the memory range specified [...] and maps it for the
>> > device(s) [...].  This memory range also is added to the same tracking
>> > mechanism as cuMemHostAlloc to automatically accelerate [...]"?  (No
>> > manual 'mlock'ing involved in that case, too; presumably again using this
>> > interface likely circumvents any "annoying" 'ulimit' limitations?)
>> >
>> > Such a *register* abstraction can then be implemented by all the libgomp
>> > offloading plugins: they just call the respective
>> > CUDA/HSA/etc. functions to register such (existing, 'malloc'ed, etc.)
>> > memory.
>> >
>> > ..., but maybe I'm missing some crucial "detail" here?
>>
>> Indeed this does appear to work; see attached
>> "[WIP] Attempt to register OpenMP pinned memory using a device instead of
>> 'mlock'".
>> Any comments (aside from the TODOs that I'm still working on)?

With those TODOs resolved, I've now pushed to devel/omp/gcc-12
commit a5a4800e92773da7126c00a9c79b172494d58ab5
"Attempt to register OpenMP pinned memory using a device instead of 'mlock'",
see attached.


> The mmap implementation was not optimized for a lot of small allocations, and I can't see that issue changing here

That's correct, 'mmap' remains.  Under the hood, 'cuMemHostRegister' must
surely also be doing some 'mlock'-like thing, so I figured it's best to
feed page-boundary memory regions to it, which 'mmap' gets us.

> so I don't know if this can be used for mlockall replacement.
>
> I had assumed that using the Cuda allocator would fix that limitation.

From what I've read (but no first-hand experiments), there's non-trivial
overhead with 'cuMemHostRegister' (just like with 'mlock'), so routing
all small allocations individually through it probably isn't a good idea
either.  Therefore, I suppose, we'll indeed want to use some local
allocator if we wish this "optimized for a lot of small allocations".

And, getting rid of 'mlockall' is yet another topic.


Grüße
 Thomas


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Comments

Thomas Schwinge Feb. 17, 2023, 8:12 a.m. UTC | #1
Hi Andrew!

On 2023-02-16T23:06:44+0100, I wrote:
> On 2023-02-16T16:17:32+0000, "Stubbs, Andrew via Gcc-patches" <gcc-patches@gcc.gnu.org> wrote:
>> The mmap implementation was not optimized for a lot of small allocations, and I can't see that issue changing here
>
> That's correct, 'mmap' remains.  Under the hood, 'cuMemHostRegister' must
> surely also be doing some 'mlock'-like thing, so I figured it's best to
> feed page-boundary memory regions to it, which 'mmap' gets us.
>
>> so I don't know if this can be used for mlockall replacement.
>>
>> I had assumed that using the Cuda allocator would fix that limitation.
>
> From what I've read (but no first-hand experiments), there's non-trivial
> overhead with 'cuMemHostRegister' (just like with 'mlock'), so routing
> all small allocations individually through it probably isn't a good idea
> either.  Therefore, I suppose, we'll indeed want to use some local
> allocator if we wish this "optimized for a lot of small allocations".

Eh, I suppose your point indirectly was that instead of 'mmap' plus
'cuMemHostRegister' we ought to use 'cuMemAllocHost'/'cuMemHostAlloc', as
we assume those already do implement such a local allocator.  Let me
quickly change that indeed -- we don't currently have a need to use
'cuMemHostRegister' instead of 'cuMemAllocHost'/'cuMemHostAlloc'.

> And, getting rid of 'mlockall' is yet another topic.

Here, the need to use 'cuMemHostRegister' may then again come up, as
begun to discuss as my "different idea" re "-foffload-memory=pinned",
<https://inbox.sourceware.org/gcc-patches/87sff9zl3u.fsf@euler.schwinge.homeip.net>.
(Let's continue that discussion there.)


Grüße
 Thomas
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Andrew Stubbs Feb. 20, 2023, 9:48 a.m. UTC | #2
On 17/02/2023 08:12, Thomas Schwinge wrote:
> Hi Andrew!
> 
> On 2023-02-16T23:06:44+0100, I wrote:
>> On 2023-02-16T16:17:32+0000, "Stubbs, Andrew via Gcc-patches" <gcc-patches@gcc.gnu.org> wrote:
>>> The mmap implementation was not optimized for a lot of small allocations, and I can't see that issue changing here
>>
>> That's correct, 'mmap' remains.  Under the hood, 'cuMemHostRegister' must
>> surely also be doing some 'mlock'-like thing, so I figured it's best to
>> feed page-boundary memory regions to it, which 'mmap' gets us.
>>
>>> so I don't know if this can be used for mlockall replacement.
>>>
>>> I had assumed that using the Cuda allocator would fix that limitation.
>>
>>  From what I've read (but no first-hand experiments), there's non-trivial
>> overhead with 'cuMemHostRegister' (just like with 'mlock'), so routing
>> all small allocations individually through it probably isn't a good idea
>> either.  Therefore, I suppose, we'll indeed want to use some local
>> allocator if we wish this "optimized for a lot of small allocations".
> 
> Eh, I suppose your point indirectly was that instead of 'mmap' plus
> 'cuMemHostRegister' we ought to use 'cuMemAllocHost'/'cuMemHostAlloc', as
> we assume those already do implement such a local allocator.  Let me
> quickly change that indeed -- we don't currently have a need to use
> 'cuMemHostRegister' instead of 'cuMemAllocHost'/'cuMemHostAlloc'.


Yes, that's right. I suppose it makes sense to register memory we 
already have, but if we want new memory then trying to reinvent what 
happens inside cuMemAllocHost is pointless.

Andrew
diff mbox series

Patch

From a5a4800e92773da7126c00a9c79b172494d58ab5 Mon Sep 17 00:00:00 2001
From: Thomas Schwinge <thomas@codesourcery.com>
Date: Thu, 16 Feb 2023 15:57:37 +0100
Subject: [PATCH] Attempt to register OpenMP pinned memory using a device
 instead of 'mlock'

Implemented for nvptx offloading via 'cuMemHostRegister'.  This means: (a) not
running into 'mlock' limitations, and (b) the device is aware of this and may
optimize host <-> device memory transfers.

This re-works og12 commit ab7520b3b4cd9fdabfd63652badde478955bd3b5
"libgomp: pinned memory".

	include/
	* cuda/cuda.h (cuMemHostRegister, cuMemHostUnregister): New.
	libgomp/
	* config/linux/allocator.c (linux_memspace_alloc)
	(linux_memspace_free, linux_memspace_realloc): Attempt to register
	OpenMP pinned memory using a device instead of 'mlock'.
	* libgomp-plugin.h (GOMP_OFFLOAD_register_page_locked)
	(GOMP_OFFLOAD_unregister_page_locked): New.
	* libgomp.h (gomp_register_page_locked)
	(gomp_unregister_page_locked): New
	(struct gomp_device_descr): Add 'register_page_locked_func',
	'unregister_page_locked_func'.
	* plugin/cuda-lib.def (cuMemHostRegister_v2, cuMemHostRegister)
	(cuMemHostUnregister): New.
	* plugin/plugin-nvptx.c (GOMP_OFFLOAD_register_page_locked)
	(GOMP_OFFLOAD_unregister_page_locked): New.
	* target.c (gomp_register_page_locked)
	(gomp_unregister_page_locked): New.
	(gomp_load_plugin_for_device): Handle 'register_page_locked',
	'unregister_page_locked'.
	* testsuite/libgomp.c/alloc-pinned-1.c: Adjust.
	* 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.
---
 include/ChangeLog.omp                        |   4 +
 include/cuda/cuda.h                          |   3 +
 libgomp/ChangeLog.omp                        |  24 ++++
 libgomp/config/linux/allocator.c             |  74 +++++++++-
 libgomp/libgomp-plugin.h                     |   2 +
 libgomp/libgomp.h                            |   4 +
 libgomp/plugin/cuda-lib.def                  |   3 +
 libgomp/plugin/plugin-nvptx.c                |  33 +++++
 libgomp/target.c                             | 137 +++++++++++++++++++
 libgomp/testsuite/libgomp.c/alloc-pinned-1.c |  25 ++++
 libgomp/testsuite/libgomp.c/alloc-pinned-2.c |  25 ++++
 libgomp/testsuite/libgomp.c/alloc-pinned-3.c |  43 +++++-
 libgomp/testsuite/libgomp.c/alloc-pinned-4.c |  43 +++++-
 libgomp/testsuite/libgomp.c/alloc-pinned-5.c |  25 ++++
 libgomp/testsuite/libgomp.c/alloc-pinned-6.c |  34 ++++-
 15 files changed, 460 insertions(+), 19 deletions(-)

diff --git a/include/ChangeLog.omp b/include/ChangeLog.omp
index 190ae67a321..c8ef7a83c58 100644
--- a/include/ChangeLog.omp
+++ b/include/ChangeLog.omp
@@ -1,3 +1,7 @@ 
+2023-02-16  Thomas Schwinge  <thomas@codesourcery.com>
+
+	* cuda/cuda.h (cuMemHostRegister, cuMemHostUnregister): New.
+
 2023-02-09  Kwok Cheung Yeung  <kcy@codesourcery.com>
 
 	* gomp-constants.h (GOMP_MAP_FLAG_SPECIAL_5): New.
diff --git a/include/cuda/cuda.h b/include/cuda/cuda.h
index 062d394b95f..b0c7636d318 100644
--- a/include/cuda/cuda.h
+++ b/include/cuda/cuda.h
@@ -183,6 +183,9 @@  CUresult cuMemAlloc (CUdeviceptr *, size_t);
 CUresult cuMemAllocHost (void **, size_t);
 CUresult cuMemAllocManaged(CUdeviceptr *, size_t, unsigned int);
 CUresult cuMemHostAlloc (void **, size_t, unsigned int);
+#define cuMemHostRegister cuMemHostRegister_v2
+CUresult cuMemHostRegister(void *, size_t, unsigned int);
+CUresult cuMemHostUnregister(void *);
 CUresult cuMemcpy (CUdeviceptr, CUdeviceptr, size_t);
 #define cuMemcpyDtoDAsync cuMemcpyDtoDAsync_v2
 CUresult cuMemcpyDtoDAsync (CUdeviceptr, CUdeviceptr, size_t, CUstream);
diff --git a/libgomp/ChangeLog.omp b/libgomp/ChangeLog.omp
index 819a5333907..7e464566a21 100644
--- a/libgomp/ChangeLog.omp
+++ b/libgomp/ChangeLog.omp
@@ -1,5 +1,29 @@ 
 2023-02-16  Thomas Schwinge  <thomas@codesourcery.com>
 
+	* config/linux/allocator.c (linux_memspace_alloc)
+	(linux_memspace_free, linux_memspace_realloc): Attempt to register
+	OpenMP pinned memory using a device instead of 'mlock'.
+	* libgomp-plugin.h (GOMP_OFFLOAD_register_page_locked)
+	(GOMP_OFFLOAD_unregister_page_locked): New.
+	* libgomp.h (gomp_register_page_locked)
+	(gomp_unregister_page_locked): New
+	(struct gomp_device_descr): Add 'register_page_locked_func',
+	'unregister_page_locked_func'.
+	* plugin/cuda-lib.def (cuMemHostRegister_v2, cuMemHostRegister)
+	(cuMemHostUnregister): New.
+	* plugin/plugin-nvptx.c (GOMP_OFFLOAD_register_page_locked)
+	(GOMP_OFFLOAD_unregister_page_locked): New.
+	* target.c (gomp_register_page_locked)
+	(gomp_unregister_page_locked): New.
+	(gomp_load_plugin_for_device): Handle 'register_page_locked',
+	'unregister_page_locked'.
+	* testsuite/libgomp.c/alloc-pinned-1.c: Adjust.
+	* 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.
+
 	* allocator.c (omp_realloc): Route 'free' through 'MEMSPACE_FREE'.
 
 	* config/linux/allocator.c (linux_memspace_alloc)
diff --git a/libgomp/config/linux/allocator.c b/libgomp/config/linux/allocator.c
index f278e5cdf14..81e64b268e9 100644
--- a/libgomp/config/linux/allocator.c
+++ b/libgomp/config/linux/allocator.c
@@ -24,6 +24,10 @@ 
 
 /* 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 register such using a device (really: libgomp
+   plugin), but fall back to 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
@@ -37,6 +41,7 @@ 
 #define _GNU_SOURCE
 #include <sys/mman.h>
 #include <string.h>
+#include <assert.h>
 #include "libgomp.h"
 
 static bool always_pinned_mode = false;
@@ -53,9 +58,15 @@  GOMP_enable_pinned_mode ()
     always_pinned_mode = true;
 }
 
+static int using_device_for_register_page_locked
+  = /* uninitialized */ -1;
+
 static void *
 linux_memspace_alloc (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;
 
@@ -71,11 +82,32 @@  linux_memspace_alloc (omp_memspace_handle_t memspace, size_t size, int pin)
       if (addr == MAP_FAILED)
 	return NULL;
 
-      if (mlock (addr, size))
+      int using_device
+	= __atomic_load_n (&using_device_for_register_page_locked,
+			   MEMMODEL_RELAXED);
+      gomp_debug (0, "  using_device=%d\n",
+		  using_device);
+      if (using_device != 0)
+	{
+	  using_device = gomp_register_page_locked (addr, size);
+	  int using_device_old
+	    = __atomic_exchange_n (&using_device_for_register_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, "libgomp: failed to pin memory (ulimit too low?)\n");
-	  munmap (addr, size);
-	  return NULL;
+	  gomp_debug (0, "  mlock\n");
+	  if (mlock (addr, size))
+	    {
+	      gomp_debug (0, "libgomp: failed to pin memory (ulimit too low?)\n");
+	      munmap (addr, size);
+	      return NULL;
+	    }
 	}
 
       return addr;
@@ -87,6 +119,9 @@  linux_memspace_alloc (omp_memspace_handle_t memspace, size_t size, int pin)
 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;
 
@@ -107,13 +142,28 @@  static void
 linux_memspace_free (omp_memspace_handle_t memspace, void *addr, size_t size,
 		     int pin)
 {
+  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 (memspace == ompx_unified_shared_mem_space)
     gomp_usm_free (addr, GOMP_DEVICE_ICV);
   else if (pin)
-    munmap (addr, size);
+    {
+      int using_device
+	= __atomic_load_n (&using_device_for_register_page_locked,
+			   MEMMODEL_RELAXED);
+      gomp_debug (0, "  using_device=%d\n",
+		  using_device);
+      if (using_device == 1)
+	gomp_unregister_page_locked (addr, size);
+      else
+	/* 'munlock'ing is implicit with following 'munmap'.  */
+	;
+      munmap (addr, size);
+    }
   else
     free (addr);
 }
@@ -122,6 +172,9 @@  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;
 
@@ -129,6 +182,17 @@  linux_memspace_realloc (omp_memspace_handle_t memspace, void *addr,
     goto manual_realloc;
   else if (oldpin && pin)
     {
+      /* We can only expect to be able to just 'mremap' if not using a device
+	 for registering page-locked memory.  */
+      int using_device
+	= __atomic_load_n (&using_device_for_register_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;
diff --git a/libgomp/libgomp-plugin.h b/libgomp/libgomp-plugin.h
index bb79ef8d9d7..345fc62d4f5 100644
--- a/libgomp/libgomp-plugin.h
+++ b/libgomp/libgomp-plugin.h
@@ -144,6 +144,8 @@  extern bool GOMP_OFFLOAD_free (int, void *);
 extern void *GOMP_OFFLOAD_usm_alloc (int, size_t);
 extern bool GOMP_OFFLOAD_usm_free (int, void *);
 extern bool GOMP_OFFLOAD_is_usm_ptr (void *);
+extern bool GOMP_OFFLOAD_register_page_locked (void *, size_t);
+extern bool GOMP_OFFLOAD_unregister_page_locked (void *, size_t);
 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 c001b468252..a5fa3f9daab 100644
--- a/libgomp/libgomp.h
+++ b/libgomp/libgomp.h
@@ -1133,6 +1133,8 @@  extern void gomp_target_rev (uint64_t, uint64_t, uint64_t, uint64_t, uint64_t,
 			     void *);
 extern void * gomp_usm_alloc (size_t size, int device_num);
 extern void gomp_usm_free (void *device_ptr, int device_num);
+extern bool gomp_register_page_locked (void *, size_t);
+extern void gomp_unregister_page_locked (void *, size_t);
 
 /* Splay tree definitions.  */
 typedef struct splay_tree_node_s *splay_tree_node;
@@ -1392,6 +1394,8 @@  struct gomp_device_descr
   __typeof (GOMP_OFFLOAD_usm_alloc) *usm_alloc_func;
   __typeof (GOMP_OFFLOAD_usm_free) *usm_free_func;
   __typeof (GOMP_OFFLOAD_is_usm_ptr) *is_usm_ptr_func;
+  __typeof (GOMP_OFFLOAD_register_page_locked) *register_page_locked_func;
+  __typeof (GOMP_OFFLOAD_unregister_page_locked) *unregister_page_locked_func;
   __typeof (GOMP_OFFLOAD_dev2host) *dev2host_func;
   __typeof (GOMP_OFFLOAD_host2dev) *host2dev_func;
   __typeof (GOMP_OFFLOAD_dev2dev) *dev2dev_func;
diff --git a/libgomp/plugin/cuda-lib.def b/libgomp/plugin/cuda-lib.def
index 9b786c9f2f6..8dbaadf848e 100644
--- a/libgomp/plugin/cuda-lib.def
+++ b/libgomp/plugin/cuda-lib.def
@@ -31,6 +31,9 @@  CUDA_ONE_CALL (cuMemAlloc)
 CUDA_ONE_CALL (cuMemAllocHost)
 CUDA_ONE_CALL (cuMemAllocManaged)
 CUDA_ONE_CALL (cuMemHostAlloc)
+CUDA_ONE_CALL_MAYBE_NULL (cuMemHostRegister_v2)
+CUDA_ONE_CALL (cuMemHostRegister)
+CUDA_ONE_CALL (cuMemHostUnregister)
 CUDA_ONE_CALL (cuMemcpy)
 CUDA_ONE_CALL (cuMemcpyDtoDAsync)
 CUDA_ONE_CALL (cuMemcpyDtoH)
diff --git a/libgomp/plugin/plugin-nvptx.c b/libgomp/plugin/plugin-nvptx.c
index 8e7b63bd637..698317f37ac 100644
--- a/libgomp/plugin/plugin-nvptx.c
+++ b/libgomp/plugin/plugin-nvptx.c
@@ -77,11 +77,14 @@  extern CUresult cuGetErrorString (CUresult, const char **);
 CUresult cuLinkAddData (CUlinkState, CUjitInputType, void *, size_t,
 			const char *, unsigned, CUjit_option *, void **);
 CUresult cuLinkCreate (unsigned, CUjit_option *, void **, CUlinkState *);
+#undef cuMemHostRegister
+CUresult cuMemHostRegister (void *, size_t, unsigned int);
 #else
 typedef size_t (*CUoccupancyB2DSize)(int);
 CUresult cuLinkAddData_v2 (CUlinkState, CUjitInputType, void *, size_t,
 			   const char *, unsigned, CUjit_option *, void **);
 CUresult cuLinkCreate_v2 (unsigned, CUjit_option *, void **, CUlinkState *);
+CUresult cuMemHostRegister_v2 (void *, size_t, unsigned int);
 CUresult cuOccupancyMaxPotentialBlockSize(int *, int *, CUfunction,
 					  CUoccupancyB2DSize, size_t, int);
 #endif
@@ -1704,6 +1707,36 @@  GOMP_OFFLOAD_is_usm_ptr (void *ptr)
   return managed;
 }
 
+
+bool
+GOMP_OFFLOAD_register_page_locked (void *ptr, size_t size)
+{
+  GOMP_PLUGIN_debug (0, "nvptx %s: ptr=%p, size=%llu\n",
+		     __FUNCTION__, ptr, (unsigned long long) size);
+
+  unsigned int flags = 0;
+  /* Given 'CU_DEVICE_ATTRIBUTE_UNIFIED_ADDRESSING', we don't need
+     'flags |= CU_MEMHOSTREGISTER_PORTABLE;' here.  */
+  if (CUDA_CALL_EXISTS (cuMemHostRegister_v2))
+    CUDA_CALL (cuMemHostRegister_v2, ptr, size, flags);
+  else
+    CUDA_CALL (cuMemHostRegister, ptr, size, flags);
+
+  return true;
+}
+
+bool
+GOMP_OFFLOAD_unregister_page_locked (void *ptr, size_t size)
+{
+  GOMP_PLUGIN_debug (0, "nvptx %s: ptr=%p, size=%llu\n",
+		     __FUNCTION__, ptr, (unsigned long long) size);
+
+  CUDA_CALL (cuMemHostUnregister, ptr);
+
+  return true;
+}
+
+
 void
 GOMP_OFFLOAD_openacc_exec (void (*fn) (void *), size_t mapnum,
 			   void **hostaddrs, void **devaddrs,
diff --git a/libgomp/target.c b/libgomp/target.c
index 1b911c9bdb9..e7285188d1e 100644
--- a/libgomp/target.c
+++ b/libgomp/target.c
@@ -4584,6 +4584,141 @@  gomp_usm_free (void *device_ptr, int device_num)
   gomp_mutex_unlock (&devicep->lock);
 }
 
+
+/* Device (really: libgomp plugin) for registering 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_register_page_locked
+  = /* uninitialized */ (void *) -1;
+
+static struct gomp_device_descr *
+get_device_for_register_page_locked (void)
+{
+  gomp_debug (0, "%s\n",
+	      __FUNCTION__);
+
+  struct gomp_device_descr *device;
+#ifdef HAVE_SYNC_BUILTINS
+  device
+    = __atomic_load_n (&device_for_register_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].register_page_locked_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"
+			" to register page-locked memory",
+			device->name, devices[i].name);
+	  else
+	    device = &devices[i];
+	}
+
+      struct gomp_device_descr *device_old
+	= __atomic_exchange_n (&device_for_register_page_locked, device,
+			       MEMMODEL_RELAXED);
+      gomp_debug (0, "  old device_for_register_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_register_page_locked;
+  device = NULL;
+#endif /* HAVE_SYNC_BUILTINS */
+
+  gomp_debug (0, "  -> device=%p (%s)\n",
+	      device, device ? device->name : "[none]");
+  return device;
+}
+
+/* Register page-locked memory region.
+   Returns whether we have a device capable of that.  */
+
+attribute_hidden bool
+gomp_register_page_locked (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_register_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 for registering page-locked memory"
+		      " is finalized", device->name);
+	}
+      gomp_mutex_unlock (&device->lock);
+
+      if (!device->register_page_locked_func (ptr, size))
+	gomp_fatal ("Failed to register page-locked memory"
+		    " via %s libgomp plugin",
+		    device->name);
+    }
+  return device != NULL;
+}
+
+/* Unregister page-locked memory region.
+   This must only be called if 'gomp_register_page_locked' returned 'true'.  */
+
+attribute_hidden void
+gomp_unregister_page_locked (void *ptr, size_t size)
+{
+  gomp_debug (0, "%s: ptr=%p\n",
+	      __FUNCTION__, ptr);
+
+  struct gomp_device_descr *device = get_device_for_register_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->unregister_page_locked_func (ptr, size))
+    gomp_fatal ("Failed to unregister page-locked memory"
+		" via %s libgomp plugin",
+		device->name);
+}
+
+
 int
 omp_target_is_present (const void *ptr, int device_num)
 {
@@ -5268,6 +5403,8 @@  gomp_load_plugin_for_device (struct gomp_device_descr *device,
   DLSYM_OPT (usm_alloc, usm_alloc);
   DLSYM_OPT (usm_free, usm_free);
   DLSYM_OPT (is_usm_ptr, is_usm_ptr);
+  DLSYM_OPT (register_page_locked, register_page_locked);
+  DLSYM_OPT (unregister_page_locked, unregister_page_locked);
   DLSYM (dev2host);
   DLSYM (host2dev);
   DLSYM (evaluate_device);
diff --git a/libgomp/testsuite/libgomp.c/alloc-pinned-1.c b/libgomp/testsuite/libgomp.c/alloc-pinned-1.c
index fb7ac8b0080..bd71e22b003 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>
@@ -67,9 +69,14 @@  verify0 (char *p, size_t s)
 int
 main ()
 {
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* Go big or go home.  */
+  const int SIZE = 40 * 1024 * 1024;
+#else
   /* Allocate at least a page each time, but stay within the ulimit.  */
   const int SIZE = PAGE_SIZE;
   CHECK_SIZE (SIZE*3);
+#endif
 
   const omp_alloctrait_t traits[] = {
       { omp_atk_pinned, 1 }
@@ -85,19 +92,37 @@  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
 
   p = omp_calloc (1, SIZE, 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);
 
diff --git a/libgomp/testsuite/libgomp.c/alloc-pinned-2.c b/libgomp/testsuite/libgomp.c/alloc-pinned-2.c
index 651b89fb42f..c71248b046d 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>
@@ -67,9 +69,14 @@  verify0 (char *p, size_t s)
 int
 main ()
 {
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* Go big or go home.  */
+  const int SIZE = 40 * 1024 * 1024;
+#else
   /* Allocate at least a page each time, but stay within the ulimit.  */
   const int SIZE = PAGE_SIZE;
   CHECK_SIZE (SIZE*3);
+#endif
 
   const omp_alloctrait_t traits[] = {
       { omp_atk_pinned, 1 },
@@ -87,23 +94,41 @@  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
 
   p = omp_calloc (1, SIZE, allocator);
   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);
 
diff --git a/libgomp/testsuite/libgomp.c/alloc-pinned-3.c b/libgomp/testsuite/libgomp.c/alloc-pinned-3.c
index f41797881ef..26b0c352d85 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>
@@ -74,8 +76,14 @@  verify0 (char *p, size_t s)
 int
 main ()
 {
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* Go big or go home.  */
+  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[] = {
@@ -92,21 +100,33 @@  main ()
   omp_allocator_handle_t allocator2 = omp_init_allocator (omp_default_mem_space, 2, traits2);
 
   /* 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);
@@ -119,16 +139,29 @@  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-4.c b/libgomp/testsuite/libgomp.c/alloc-pinned-4.c
index a878da8c558..0bd6a552d94 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>
@@ -74,8 +76,14 @@  verify0 (char *p, size_t s)
 int
 main ()
 {
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* Go big or go home.  */
+  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[] = {
@@ -94,21 +102,33 @@  main ()
   omp_allocator_handle_t allocator2 = omp_init_allocator (omp_default_mem_space, 3, traits2);
 
   /* 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);
@@ -121,16 +141,29 @@  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 65983b3d03d..623c96a78e3 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>
@@ -67,9 +69,14 @@  verify0 (char *p, size_t s)
 int
 main ()
 {
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* Go big or go home.  */
+  const int SIZE = 40 * 1024 * 1024;
+#else
   /* Allocate at least a page each time, but stay within the ulimit.  */
   const int SIZE = PAGE_SIZE;
   CHECK_SIZE (SIZE*3);
+#endif
 
   // Sanity check
   if (get_pinned_mem () != 0)
@@ -80,19 +87,37 @@  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
 
   p = omp_calloc (1, SIZE, 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);
 
diff --git a/libgomp/testsuite/libgomp.c/alloc-pinned-6.c b/libgomp/testsuite/libgomp.c/alloc-pinned-6.c
index bbe20c04875..c0f8b260e37 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 +68,55 @@  set_pin_limit ()
 int
 main ()
 {
+#ifdef OFFLOAD_DEVICE_NVPTX
+  /* Go big or go home.  */
+  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 ();
-- 
2.25.1