Isolate macOS from Linux mmap optimizations.

include/bitcoin/database/impl/memory/mmap_staging.ipp

@@ -938,10 +938,15 @@ void CLASS::settler_run_() NOEXCEPT
         }
 #endif
 
+#if !defined(HAVE_APPLE)
         // Scarcity is read directly: clean cache is reclaimable, so the
         // kernel pressure level does not raise while free memory exhausts.
+        // Apple is excluded: the sweep corrects linux victim selection, and
+        // ubc/compressor reclaim measured competent without it (its free
+        // signal is also perpetually low on darwin, running the sweep hot).
         if (system_free() < scarce)
             evict_next_(sweep);
+#endif
 
         auto bytes = backlog();
         if (is_zero(bytes))
@@ -998,6 +1003,7 @@ void CLASS::head_run_() NOEXCEPT
         still = (top == mark) ? std::min(add1(still), idle_seconds) : zero;
         mark = top;
 
+#if !defined(HAVE_APPLE)
         // Touch pass: assert working-set residency at a bounded rate.
         // Hash-uniform probing is per-page sparse in every phase, so the
         // kernel ages head pages cold and swaps them under cache pressure,
@@ -1041,6 +1047,7 @@ void CLASS::head_run_() NOEXCEPT
                 }
             }
         }
+#endif // !HAVE_APPLE
 
         if ((still < idle_seconds) || (transferred == top))
             continue;

include/bitcoin/database/memory/settings.hpp

@@ -60,8 +60,14 @@ struct storage_settings
     /// scattered: they are far too large to reside, and validation reads
     /// prevouts from arbitrary earlier blocks, so read-ahead manufactures
     /// cache that is never used and displaces the resident head set. Heads
-    /// override to random (preloaded) at construction.
+    /// override to random (preloaded) at construction. Apple retains normal
+    /// (its measured known-good): darwin fault clustering serves scattered
+    /// prevout reads that MADV_RANDOM would reduce to single-page faults.
+#if defined(HAVE_APPLE)
+    advice access{ advice::normal };
+#else
     advice access{ advice::scattered };
+#endif
 };
 
 } // namespace database