From 4143e12a29ae6aab5615add83d0406cdee7a3738 Mon Sep 17 00:00:00 2001
From: Max Wash <mbswash@gmail.com>
Date: Wed, 1 Apr 2026 18:32:32 +0100
Subject: [PATCH] vm: add a copy-on-write ref count to vm_page

---
 include/kernel/vm.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/kernel/vm.h b/include/kernel/vm.h
index 4fc2e78..ef62403 100644
--- a/include/kernel/vm.h
+++ b/include/kernel/vm.h
@@ -1,6 +1,7 @@
 #ifndef KERNEL_VM_H_
 #define KERNEL_VM_H_
 
+#include <kernel/atomic.h>
 #include <kernel/bitmap.h>
 #include <kernel/btree.h>
 #include <kernel/locks.h>
@@ -221,6 +222,9 @@ struct vm_page {
 	};
 
 	union {
+		/* how many vm_areas reference this vm_page. if >0, the page is
+		 * subject to copy-on-write. */
+		atomic_t p_cow_ref;
 		uint32_t p_priv2;
 	};