libgomp, nvptx: Cuda pinned memory

libgomp, nvptx: Cuda pinned memory

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.
	* 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>
(cherry picked from commit 3b8d9d579c2931f1d8d2c89ff67735bc77df55ad)