From 79bbbc074bd1d96bb56256bc0e4c6603a93673af Mon Sep 17 00:00:00 2001
From: Chloe M <chloe@yiffware.org>
Date: Fri, 10 Jul 2026 19:07:11 -0400
Subject: [PATCH] ptos: pm: Add frame allocation and reclamation

Signed-off-by: Chloe M <chloe@yiffware.org>
---
 service/ptos/head/mm/pm.h |  17 +++++
 service/ptos/mm/pm.c      | 145 +++++++++++++++++++++++++++++++++++++-
 2 files changed, 159 insertions(+), 3 deletions(-)

diff --git a/service/ptos/head/mm/pm.h b/service/ptos/head/mm/pm.h
index 0b56361..74899d9 100644
--- a/service/ptos/head/mm/pm.h
+++ b/service/ptos/head/mm/pm.h
@@ -12,6 +12,9 @@
 #include <ptdef.h>
 #include <hal/page.h>
 
+/* Used when out of memory */
+#define PFN_ERROR 0
+
 /* Page frame number type */
 typedef USIZE MM_PFN;
 
@@ -29,4 +32,18 @@ typedef USIZE MM_PFN;
  */
 VOID MmPmInit(VOID);
 
+/*
+ * Request a single frame of memory
+ *
+ * Returns PFN_ERROR on failure
+ */
+MM_PFN MmRequestFrame(VOID);
+
+/*
+ * Reclaim a single frame of memory
+ *
+ * @Pfn:  Page frame number to reclaim
+ */
+VOID MmReclaimFrame(MM_PFN Pfn);
+
 #endif  /* !_MM_PM_H_ */
diff --git a/service/ptos/mm/pm.c b/service/ptos/mm/pm.c
index ca537cf..0712f74 100644
--- a/service/ptos/mm/pm.c
+++ b/service/ptos/mm/pm.c
@@ -7,8 +7,10 @@
  */
 
 #include <mm/pm.h>
+#include <mm/vm.h>
 #include <ke/bpal.h>
 #include <ex/trace.h>
+#include <string.h>
 
 #define DTRACE(Fmt, ...) \
     TRACE("[ PM ]: " Fmt, ##__VA_ARGS__)
@@ -34,6 +36,88 @@ static const CHAR *PmRegionTable[] = {
     [MEMORY_ACPI_TABLES]    = "acpi tables"
 };
 
+/*
+ * A page frame descriptor is an entry within the physical memory
+ * freelist.
+ *
+ * @Next:  Next PFD in freelist
+ * @Prev:  Previous PFD in freelist
+ */
+typedef struct _MM_PFD {
+    struct _MM_PFD *Next;
+    struct _MM_PFD *Prev;
+} MM_PFD;
+
+/*
+ * A page frame descriptor list holds many page frame
+ * descriptors and marks the start and end of a physical
+ * memory freelist.
+ *
+ * @First: First entry in freelist
+ * @Last:  Last entry in freelist
+ *
+ * TODO: Add a lock to this structure
+ */
+typedef struct {
+    MM_PFD *First;
+    MM_PFD *Last;
+} MM_PFD_LIST;
+
+/* Standard usable memory list */
+static MM_PFD_LIST AvlList;
+
+/*
+ * Appends a page frame descriptor to a page frame descriptor
+ * list.
+ *
+ * @List: Page frame descriptor list to append to
+ * @Pfd:  Page frame descriptor to append
+ */
+static VOID
+PmPfdListAppend(MM_PFD_LIST *List, MM_PFD *Pfd)
+{
+    MM_PFD *LastPfd;
+
+    if (List == NULL || Pfd == NULL) {
+        return;
+    }
+
+    Pfd->Next = NULL;
+    Pfd->Prev = NULL;
+
+    if (List->First == NULL || List->Last == NULL) {
+        List->First = Pfd;
+        List->Last = Pfd;
+    } else {
+        LastPfd = List->Last;
+        LastPfd->Next = Pfd;
+        Pfd->Prev = LastPfd;
+        List->Last = Pfd;
+    }
+}
+
+/*
+ * Pop a page frame descriptor from the beginning of a page
+ * frame descriptor list.
+ *
+ * @List: Page frame descriptor list to pop from
+ *
+ * Returns NULL on failure
+ */
+static MM_PFD *
+PmPfdListPop(MM_PFD_LIST *List)
+{
+    MM_PFD *FirstPfd;
+
+    if (List == NULL) {
+        return NULL;
+    }
+
+    FirstPfd = List->First;
+    List->First = FirstPfd->Next;
+    return FirstPfd;
+}
+
 /*
  * Probe physical memory for usable regions and list
  * installed memory.
@@ -44,8 +128,10 @@ PmProbe(VOID)
     PT_STATUS Status;
     BPAL_HANDLE BpalHandle;
     MEMMAP_ENTRY Entry;
-    UPTR Start, End;
-    USIZE Index;
+    UPTR Start, End, Off;
+    MM_PFD *PfdBase, *PfdCurrent;
+    USIZE Index, PfdCount = 0;
+    USIZE ZoneCount = 0;
 
     /*
      * We obtain memory map entries from the BPAL layer as it is provided
@@ -53,7 +139,15 @@ PmProbe(VOID)
      */
     KeBpalGetHandle(&BpalHandle);
 
-    /* Iterate each memory entry */
+    /*
+     * Iterate each memory entry, we use two terms here:
+     *
+     * Zones: A zone is a contigious region of frames and consists
+     *        of many page frame descriptors.
+     *
+     * PFDs:  A page frame descriptor represents a single frame within
+     *        a zone.
+     */
     for (Index = 0;; ++Index) {
         Status = BpalHandle.MemEntryIdx(Index, &Entry);
 
@@ -70,7 +164,52 @@ PmProbe(VOID)
             End,
             PM_REGION(Entry.Type)
         );
+
+        /* Usable entries from this point only */
+        if (Entry.Type != MEMORY_USABLE) {
+            continue;
+        }
+
+        /* Append this zone */
+        PfdBase = (MM_PFD *)PMA_TO_VMA(Entry.Base);
+        for (Off = 0; Off < Entry.Length; Off += PAGESIZE) {
+            PfdCurrent = PTR_OFFSET(PfdBase, Off);
+            PmPfdListAppend(&AvlList, PfdCurrent);
+            ++PfdCount;
+        }
+
+        ++ZoneCount;
     }
+
+    DTRACE("%d pfds, %d zones\n", PfdCount, ZoneCount);
+}
+
+MM_PFN
+MmRequestFrame(VOID)
+{
+    MM_PFD *Pfd;
+    UPTR PhysicalBase;
+
+    Pfd = PmPfdListPop(&AvlList);
+    RtlMemSet(Pfd, 0, PAGESIZE);
+
+    PhysicalBase = (UPTR)Pfd;
+    return ADDRESS_TO_PFN(PhysicalBase);
+}
+
+VOID
+MmReclaimFrame(MM_PFN Pfn)
+{
+    MM_PFD *Pfd;
+    UPTR PhysicalBase;
+
+    if (Pfn == PFN_ERROR) {
+        return;
+    }
+
+    PhysicalBase = PFN_TO_ADDRESS(Pfn);
+    Pfd = (VOID *)PMA_TO_VMA(PhysicalBase);
+    PmPfdListAppend(&AvlList, Pfd);
 }
 
 VOID