From 49c7d6050f24676ef39b62f4e2076fc5b20f313c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Branimir=20Karad=C5=BEi=C4=87?= <branimirkaradzic@gmail.com>
Date: Wed, 21 Oct 2026 17:37:35 -0700
Subject: [PATCH] Implemented Memory::DontNeed on Windows, pages are reset and
 removed from working set. (#471)

---
 src/os.cpp        |  7 ++++++-
 tests/os_test.cpp | 24 ++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/src/os.cpp b/src/os.cpp
index 9b06ea2..fe834a0 100644
--- a/src/os.cpp
+++ b/src/os.cpp
@@ -719,7 +719,12 @@ namespace bx
 			}
 		}
 
-		BX_UNUSED(advise);
+		if (Memory::DontNeed == advise)
+		{
+			VirtualAlloc(_address, _size, MEM_RESET, PAGE_NOACCESS);
+			VirtualUnlock(_address, _size);
+		}
+
 		return _address;
 #else
 		BX_UNUSED(_address, _size, _alignment, _flags, state, protect, advise, page, granularity);
diff --git a/tests/os_test.cpp b/tests/os_test.cpp
index 238ea1a..8b4c70e 100644
--- a/tests/os_test.cpp
+++ b/tests/os_test.cpp
@@ -132,6 +132,30 @@ TEST_CASE("memoryMap-protection-change", "[os]")
 	REQUIRE(err.isOk() );
 }
 
+TEST_CASE("memoryMap-dont-need", "[os]")
+{
+	const size_t size = 16*bx::memoryPageSize();
+
+	bx::Error err;
+	void* addr = bx::memoryMap(NULL, size, 0, bx::Memory::ReadWrite, &err);
+	REQUIRE(err.isOk() );
+	REQUIRE(nullptr != addr);
+
+	uint8_t* bytes = (uint8_t*)addr;
+	bx::memSet(bytes, 0xab, size);
+
+	// Pages stay accessible after their contents are dropped.
+	bx::memoryMap(addr, size, 0, bx::Memory::DontNeed, &err);
+	REQUIRE(err.isOk() );
+
+	bx::memSet(bytes, 0xcd, size);
+	REQUIRE(0xcd == bytes[0]);
+	REQUIRE(0xcd == bytes[size-1]);
+
+	bx::memoryUnmap(addr, size, &err);
+	REQUIRE(err.isOk() );
+}
+
 TEST_CASE("memoryAllocationGranularity", "[os]")
 {
 	const size_t pageSize    = bx::memoryPageSize();