fix(memory): reserve only large regions (#608)

* fix(memory): reserve only large regions

* Potential fix for pull request finding

src/SharpEmu.Core/Memory/PhysicalVirtualMemory.cs

@@ -238,7 +238,15 @@ public sealed unsafe class PhysicalVirtualMemory : IVirtualMemory, IGuestMemoryA
         var alignedSize = (size + 0xFFF) & ~0xFFFUL;
         var protection = executable ? PAGE_EXECUTE_READWRITE : PAGE_READWRITE;
         var hostProtection = executable ? HostPageProtection.ReadWriteExecute : HostPageProtection.ReadWrite;
-        var result = _hostMemory.Allocate(desiredAddress, alignedSize, hostProtection);
+
+        // Reserve address space only for very large non-executable regions; commit is done lazily later.
+        var reservedOnly = !executable &&
+            alignedSize >= LargeDataReserveThreshold &&
+            alignedSize > FullCommitRegionLimit;
+
+        var result = reservedOnly
+            ? _hostMemory.Reserve(desiredAddress, alignedSize, HostPageProtection.ReadWrite)
+            : _hostMemory.Allocate(desiredAddress, alignedSize, hostProtection);
         if (result == 0)
         {
             return false;
@@ -252,6 +260,8 @@ public sealed unsafe class PhysicalVirtualMemory : IVirtualMemory, IGuestMemoryA
             return false;
         }
 
+        var state = reservedOnly ? ReserveRegion(actualAddress, alignedSize) : "n/a";
+
         _gate.EnterWriteLock();
         try
         {
@@ -260,7 +270,7 @@ public sealed unsafe class PhysicalVirtualMemory : IVirtualMemory, IGuestMemoryA
                 VirtualAddress = actualAddress,
                 Size = alignedSize,
                 IsExecutable = executable,
-                IsReservedOnly = false,
+                IsReservedOnly = reservedOnly,
                 Protection = protection
             });
         }
@@ -269,6 +279,7 @@ public sealed unsafe class PhysicalVirtualMemory : IVirtualMemory, IGuestMemoryA
             _gate.ExitWriteLock();
         }
 
+
         var allocationKind = executable ? "executable memory" : "data memory";
         TraceVmem($"Allocated exact {allocationKind}: 0x{actualAddress:X16} - 0x{actualAddress + alignedSize:X16} ({alignedSize} bytes)");
         return true;
@@ -361,44 +372,7 @@ public sealed unsafe class PhysicalVirtualMemory : IVirtualMemory, IGuestMemoryA
 
         var actualAddress = result;
 
-        var lazyPrimeState = "n/a";
+        var lazyPrimeState = reservedOnly ? ReserveRegion(actualAddress, alignedSize) : "n/a";
-        if (reservedOnly)
-        {
-            var primeBytes = Math.Min(alignedSize, LazyReservePrimeBytes);
-            if (primeBytes != 0)
-            {
-                ulong committedBytes = 0;
-                while (committedBytes < primeBytes)
-                {
-                    var remaining = primeBytes - committedBytes;
-                    var chunkBytes = Math.Min(remaining, LazyReservePrimeChunkBytes);
-                    var commitAddress = actualAddress + committedBytes;
-                    if (!_hostMemory.Commit(commitAddress, chunkBytes, HostPageProtection.ReadWrite))
-                    {
-                        break;
-                    }
-
-                    committedBytes += chunkBytes;
-                }
-
-                if (committedBytes != 0)
-                {
-                    lazyPrimeState = committedBytes == primeBytes
-                        ? $"ok:{committedBytes:X}"
-                        : $"partial:{committedBytes:X}/{primeBytes:X}";
-                    TraceVmem($"Primed lazy region: 0x{actualAddress:X16} - 0x{actualAddress + committedBytes:X16} ({committedBytes} bytes)");
-                }
-                else
-                {
-                    lazyPrimeState = $"fail:{primeBytes:X}";
-                    TraceVmem($"Failed to prime lazy region at 0x{actualAddress:X16} ({primeBytes} bytes), continuing with on-demand commit");
-                }
-            }
-            else
-            {
-                lazyPrimeState = "skip:0";
-            }
-        }
 
         _gate.EnterWriteLock();
         try
@@ -425,6 +399,41 @@ public sealed unsafe class PhysicalVirtualMemory : IVirtualMemory, IGuestMemoryA
         return actualAddress;
     }
 
+    private string ReserveRegion(ulong actualAddress, ulong alignedSize)
+    {
+        var primeBytes = Math.Min(alignedSize, LazyReservePrimeBytes);
+        if (primeBytes == 0)
+        {
+            return "skip:0";
+        }
+
+        ulong committedBytes = 0;
+        while (committedBytes < primeBytes)
+        {
+            var remaining = primeBytes - committedBytes;
+            var chunkBytes = Math.Min(remaining, LazyReservePrimeChunkBytes);
+            var commitAddress = actualAddress + committedBytes;
+            if (!_hostMemory.Commit(commitAddress, chunkBytes, HostPageProtection.ReadWrite))
+            {
+                break;
+            }
+
+            committedBytes += chunkBytes;
+        }
+
+        if (committedBytes != 0)
+        {
+            var state = committedBytes == primeBytes
+                ? $"ok:{committedBytes:X}"
+                : $"partial:{committedBytes:X}/{primeBytes:X}";
+            TraceVmem($"region: 0x{actualAddress:X16} - 0x{actualAddress + committedBytes:X16} ({committedBytes} bytes)");
+            return state;
+        }
+
+        TraceVmem($"Failed to reserve region at 0x{actualAddress:X16} ({primeBytes} bytes)!");
+        return $"fail:{primeBytes:X}";
+    }
+
     public bool TryBackFixedRange(ulong address, ulong size, bool executable)
     {
         if (size == 0)