From b7c004528a83d83ecee443d6e0705ab2d63c9b40 Mon Sep 17 00:00:00 2001
From: Aiken Harris <harraiken91@gmail.com>
Date: Tue, 23 Dec 2025 22:13:09 +0100
Subject: [PATCH] Implement tracking of available physical pages

---
 xtoskrnl/includes/mm/pfn.hh |  5 +++++
 xtoskrnl/mm/data.cc         |  3 +++
 xtoskrnl/mm/pfn.cc          | 30 ++++++++++++++++++++++++++++++
 3 files changed, 38 insertions(+)

diff --git a/xtoskrnl/includes/mm/pfn.hh b/xtoskrnl/includes/mm/pfn.hh
index 6473f1a..6546b2f 100644
--- a/xtoskrnl/includes/mm/pfn.hh
+++ b/xtoskrnl/includes/mm/pfn.hh
@@ -18,6 +18,7 @@ namespace MM
     class Pfn
     {
         private:
+            STATIC PFN_NUMBER AvailablePages;
             STATIC PLOADER_MEMORY_DESCRIPTOR FreeDescriptor;
             STATIC ULONG_PTR HighestPhysicalPage;
             STATIC ULONG_PTR LowestPhysicalPage;
@@ -31,6 +32,10 @@ namespace MM
             STATIC XTAPI ULONGLONG GetNumberOfPhysicalPages(VOID);
             STATIC XTAPI PFN_NUMBER GetPfnDatabaseSize(VOID);
             STATIC XTAPI VOID ScanMemoryDescriptors(VOID);
+
+        private:
+            STATIC XTAPI VOID DecrementAvailablePages(VOID);
+            STATIC XTAPI VOID IncrementAvailablePages(VOID);
     };
 }
 
diff --git a/xtoskrnl/mm/data.cc b/xtoskrnl/mm/data.cc
index be173b1..3c26171 100644
--- a/xtoskrnl/mm/data.cc
+++ b/xtoskrnl/mm/data.cc
@@ -39,6 +39,9 @@ PFN_NUMBER MM::Manager::NumberOfSystemPtes;
 /* Instance of the page map routines for the current PML level */
 MM::PPAGEMAP MM::Paging::PmlRoutines;
 
+/* Total number of physical pages available for allocation */
+PFN_NUMBER MM::Pfn::AvailablePages;
+
 /* Biggest free memory descriptor */
 PLOADER_MEMORY_DESCRIPTOR MM::Pfn::FreeDescriptor;
 
diff --git a/xtoskrnl/mm/pfn.cc b/xtoskrnl/mm/pfn.cc
index 68e3337..5a8d20e 100644
--- a/xtoskrnl/mm/pfn.cc
+++ b/xtoskrnl/mm/pfn.cc
@@ -60,6 +60,21 @@ MM::Pfn::ComputePfnDatabaseSize(VOID)
     PfnDatabaseSize >>= MM_PAGE_SHIFT;
 }
 
+/**
+ * Decrements the global count of available pages.
+ *
+ * @return This routine does not return any value.
+ *
+ * @since XT 1.0
+ */
+XTAPI
+VOID
+MM::Pfn::DecrementAvailablePages(VOID)
+{
+    /* Decrement the global count of available pages */
+    AvailablePages--;
+}
+
 /**
  * Retrieves the total number of physical pages managed by the system.
  *
@@ -90,6 +105,21 @@ MM::Pfn::GetPfnDatabaseSize(VOID)
     return PfnDatabaseSize;
 }
 
+/**
+ * Increments the global count of available pages.
+ *
+ * @return This routine does not return any value.
+ *
+ * @since XT 1.0
+ */
+XTAPI
+VOID
+MM::Pfn::IncrementAvailablePages(VOID)
+{
+    /* Increment the global count of available pages */
+    AvailablePages++;
+}
+
 /**
  * Scans memory descriptors provided by the boot loader.
  *