add option to limit OS allocation and only allow allocation from arenas

include/mimalloc.h

@@ -311,6 +311,7 @@ typedef enum mi_option_e {
   mi_option_eager_commit_delay,
   mi_option_reset_delay,
   mi_option_use_numa_nodes,
+  mi_option_limit_os_alloc,
   mi_option_os_tag,
   mi_option_max_errors,
   _mi_option_last

src/arena.c

@@ -197,6 +197,7 @@ void* _mi_arena_alloc_aligned(size_t size, size_t alignment, bool* commit, bool*
   }
 
   // finally, fall back to the OS
+  if (mi_option_is_enabled(mi_option_limit_os_alloc)) return NULL;
   *is_zero = true;
   *memid   = MI_MEMID_OS;  
   void* p = _mi_os_alloc_aligned(size, alignment, *commit, large, tld->stats);
@@ -326,7 +327,7 @@ int mi_reserve_os_memory(size_t size, bool commit, bool allow_large) mi_attr_noe
     _mi_verbose_message("failed to reserve %zu k memory\n", _mi_divide_up(size,1024));
     return ENOMEM;
   }
-  _mi_verbose_message("reserved %zu kb memory\n", _mi_divide_up(size,1024));
+  _mi_verbose_message("reserved %zu kb memory%s\n", _mi_divide_up(size,1024), large ? " (in large os pages)" : "");
   return 0;
 }
 

src/options.c

@@ -86,6 +86,7 @@ static mi_option_desc_t options[_mi_option_last] =
 #endif
   { 100, UNINIT, MI_OPTION(reset_delay) },       // reset delay in milli-seconds
   { 0,   UNINIT, MI_OPTION(use_numa_nodes) },    // 0 = use available numa nodes, otherwise use at most N nodes.
+  { 0,   UNINIT, MI_OPTION(limit_os_alloc) },    // 1 = do not use OS memory for allocation (but only reserved arenas)
   { 100, UNINIT, MI_OPTION(os_tag) },            // only apple specific for now but might serve more or less related purpose
   { 16,  UNINIT, MI_OPTION(max_errors) }         // maximum errors that are output
 };

test/test-stress.c

@@ -235,7 +235,7 @@ int main(int argc, char** argv) {
     if (n > 0) ITER = n;
   }
   printf("Using %d threads with a %d%% load-per-thread and %d iterations\n", THREADS, SCALE, ITER);
-  //mi_reserve_os_memory(512*1024*1024ULL, true, true);
+  //mi_reserve_os_memory(1024*1024*1024ULL, false, true);
   //int res = mi_reserve_huge_os_pages(4,1);
   //printf("(reserve huge: %i\n)", res);