oshmem: sshmem sysv: auto huge page alloc can fallback to regular pages.

Fallback to the regular pages if huge page allocation is set to auto
and it was not possible to allocate requested amount of memory with
the hugepages.

Signed-off-by: Alex Mikheev <alexm@mellanox.com>

oshmem/mca/sshmem/sysv/sshmem_sysv_module.c

@@ -115,6 +115,7 @@ segment_create(map_segment_t *ds_buf,
     void *addr = NULL;
     int shmid = MAP_SEGMENT_SHM_INVALID;
     int flags;
+    int try_hp;
 
     assert(ds_buf);
 
@@ -129,14 +130,28 @@ segment_create(map_segment_t *ds_buf,
      * real_size here
      */
     flags = IPC_CREAT | IPC_EXCL | S_IRUSR | S_IWUSR;
+    try_hp = mca_sshmem_sysv_component.use_hp;
 #if defined (SHM_HUGETLB)
-    flags |= ((0 != mca_sshmem_sysv_component.use_hp) ? SHM_HUGETLB : 0);
+    flags |= ((0 != try_hp) ? SHM_HUGETLB : 0);
     size = ((size + sshmem_sysv_gethugepagesize() - 1) / sshmem_sysv_gethugepagesize()) * sshmem_sysv_gethugepagesize();
 #endif
 
     /* Create a new shared memory segment and save the shmid. */
+retry_alloc:
     shmid = shmget(IPC_PRIVATE, size, flags);
     if (shmid == MAP_SEGMENT_SHM_INVALID) {
+        /* hugepage alloc was set to auto. Hopefully it failed because there are no
+         * enough hugepages on the system. Turn it off and retry.
+         */
+        if (-1 == try_hp) {
+            OPAL_OUTPUT_VERBOSE(
+                    (10, oshmem_sshmem_base_framework.framework_output,
+                     "failed to allocate %llu bytes with huge pages. "
+                     "Using regular pages", (unsigned long long)size));
+            flags = IPC_CREAT | IPC_EXCL | S_IRUSR | S_IWUSR;
+            try_hp = 0;
+            goto retry_alloc;
+        }
         opal_show_help("help-oshmem-sshmem.txt",
                        "create segment failure",
                        true,