CacheLocality: reserve less space on mobile

Summary: Mobile phones have more like 16 CPUs and less like 128 CPUs.

Reviewed By: yfeldblum

Differential Revision: D16151292

fbshipit-source-id: 87caed64d9a874f71e85ee2842194405e43568a3

folly/concurrency/CacheLocality.h

@@ -278,7 +278,10 @@ struct AccessSpreader {
  private:
   /// If there are more cpus than this nothing will crash, but there
   /// might be unnecessary sharing
-  enum { kMaxCpus = 128 };
+  enum {
+    // Android phones with 8 cores exist today; 16 for future-proofing.
+    kMaxCpus = kIsMobile ? 16 : 128,
+  };
 
   typedef uint8_t CompactStripe;