From 5224dc315f41d6354d9c12c9304aa79013eed935 Mon Sep 17 00:00:00 2001
From: Aiken Harris <harraiken91@gmail.com>
Date: Sat, 13 Dec 2025 22:50:27 +0100
Subject: [PATCH] Compute PFN database size during MM initialization

---
 xtoskrnl/includes/mm/pfn.hh |  3 +++
 xtoskrnl/mm/mmgr.cc         |  3 +++
 xtoskrnl/mm/pfn.cc          | 32 ++++++++++++++++++++++++++++++++
 3 files changed, 38 insertions(+)

diff --git a/xtoskrnl/includes/mm/pfn.hh b/xtoskrnl/includes/mm/pfn.hh
index 543d958..8682d0d 100644
--- a/xtoskrnl/includes/mm/pfn.hh
+++ b/xtoskrnl/includes/mm/pfn.hh
@@ -23,9 +23,12 @@ namespace MM
             STATIC ULONG_PTR LowestPhysicalPage;
             STATIC ULONG NumberOfPhysicalPages;
             STATIC LOADER_MEMORY_DESCRIPTOR OriginalFreeDescriptor;
+            STATIC PFN_NUMBER PfnDatabaseSize;
 
         public:
+            STATIC XTAPI VOID ComputePfnDatabaseSize(VOID);
             STATIC XTAPI ULONG GetNumberOfPhysicalPages(VOID);
+            STATIC XTAPI PFN_NUMBER GetPfnDatabaseSize(VOID);
             STATIC XTAPI VOID ScanMemoryDescriptors(VOID);
     };
 }
diff --git a/xtoskrnl/mm/mmgr.cc b/xtoskrnl/mm/mmgr.cc
index 5297ab8..9c9aea1 100644
--- a/xtoskrnl/mm/mmgr.cc
+++ b/xtoskrnl/mm/mmgr.cc
@@ -31,6 +31,9 @@ MM::Manager::InitializeMemoryManager(VOID)
         DebugPrint(L"Insufficient physical pages! Install additional memory\n");
         KE::Crash::Panic(0);
     }
+
+    /* Compute allocation size for the PFN database */
+    MM::Pfn::ComputePfnDatabaseSize();
 }
 
 /**
diff --git a/xtoskrnl/mm/pfn.cc b/xtoskrnl/mm/pfn.cc
index ac58496..84ead54 100644
--- a/xtoskrnl/mm/pfn.cc
+++ b/xtoskrnl/mm/pfn.cc
@@ -10,6 +10,23 @@
 #include <xtos.hh>
 
 
+/**
+ * Calculates the total number of pages required for the PFN database and its associated color tables.
+ *
+ * @return This routine does not return any value.
+ *
+ * @since XT 1.0
+ */
+XTAPI
+VOID
+MM::Pfn::ComputePfnDatabaseSize(VOID)
+{
+    /* Calculate the total number of pages required for the PFN database */
+    PfnDatabaseSize = (HighestPhysicalPage + 1) * sizeof(MMPFN);
+    PfnDatabaseSize = ROUND_UP(PfnDatabaseSize, MM_PAGE_SIZE);
+    PfnDatabaseSize >>= MM_PAGE_SHIFT;
+}
+
 /**
  * Retrieves the total number of physical pages managed by the system.
  *
@@ -25,6 +42,21 @@ MM::Pfn::GetNumberOfPhysicalPages(VOID)
     return NumberOfPhysicalPages;
 }
 
+/**
+ * Gets the size of the PFN database and its associated structures, in pages.
+ *
+ * @return This routine returns the total number of pages required for the PFN database and its associated structures.
+ *
+ * @since XT 1.0
+ */
+XTAPI
+PFN_NUMBER
+MM::Pfn::GetPfnDatabaseSize(VOID)
+{
+    /* Return the pre-calculated size of the PFN database in pages */
+    return PfnDatabaseSize;
+}
+
 /**
  * Scans memory descriptors provided by the boot loader.
  *