add environment option to reserve huge pages upfront

include/mimalloc.h

@@ -228,6 +228,7 @@ typedef enum mi_option_e {
   mi_option_eager_commit,
   mi_option_eager_region_commit,
   mi_option_large_os_pages,         // implies eager commit
+  mi_option_reserve_huge_os_pages,
   mi_option_page_reset,
   mi_option_cache_reset,
   mi_option_reset_decommits,

src/init.c

@@ -422,6 +422,12 @@ static void mi_process_load(void) {
   const char* msg = NULL;
   mi_allocator_init(&msg);
   if (msg != NULL) _mi_verbose_message(msg);
+
+  if (mi_option_is_enabled(mi_option_reserve_huge_os_pages)) {
+    size_t pages     = mi_option_get(mi_option_reserve_huge_os_pages);
+    double max_secs = (double)pages / 10.0; // 0.1s per page
+    mi_reserve_huge_os_pages(pages, max_secs);
+  }
 }
 
 // Initialize the process; called by thread_init or the process loader

src/options.c

@@ -58,6 +58,7 @@ static mi_option_desc_t options[_mi_option_last] =
   { 1, UNINIT, "eager_region_commit" },
   #endif
   { 0, UNINIT, "large_os_pages" },      // use large OS pages, use only with eager commit to prevent fragmentation of VMA's
+  { 0, UNINIT, "reserve_huge_os_pages" },
   { 0, UNINIT, "page_reset" },
   { 0, UNINIT, "cache_reset" },
   { 0, UNINIT, "reset_decommits" },     // note: cannot enable this if secure is on

src/os.c

@@ -108,7 +108,7 @@ void _mi_os_init(void) {
   }
   // Try to see if large OS pages are supported
   unsigned long err = 0;
-  bool ok = mi_option_is_enabled(mi_option_large_os_pages);
+  bool ok = mi_option_is_enabled(mi_option_large_os_pages) || mi_option_is_enabled(mi_option_reserve_huge_os_pages);
   if (ok) {
     // To use large pages on Windows, we first need access permission
     // Set "Lock pages in memory" permission in the group policy editor
@@ -788,6 +788,7 @@ int mi_reserve_huge_os_pages( size_t pages, double max_secs ) mi_attr_noexcept
       if (estimate > 1.5*max_secs) return (-1); // seems like we are going to timeout
     }
   }  
+  _mi_verbose_message("reserved %zu huge pages\n", pages);
   return 0;
 }
 #endif