per thread region search index

include/mimalloc-types.h

@@ -384,6 +384,7 @@ typedef struct mi_segments_tld_s {
 
 // OS thread local data
 typedef struct mi_os_tld_s {
+  size_t              region_idx;   // start point for next allocation
   mi_stats_t*         stats;        // points to tld stats
 } mi_os_tld_t;