Replace zones with individually tracked physical pages.

It's just a simple struct { ref_count, paddr }.
This will allow me to implement lazy zeroing and COW pages.

AK/RetainPtr.h

@@ -32,6 +32,7 @@ public:
     RetainPtr(RetainPtr& other) : m_ptr(other.copyRef().leakRef()) { }
     RetainPtr(RetainPtr&& other) : m_ptr(other.leakRef()) { }
     template<typename U> RetainPtr(RetainPtr<U>&& other) : m_ptr(static_cast<T*>(other.leakRef())) { }
+    RetainPtr(const RetainPtr& other) : m_ptr(const_cast<RetainPtr&>(other).copyRef().leakRef()) { }
     ~RetainPtr()
     {
         clear();
@@ -121,6 +122,8 @@ public:
 
     operator bool() { return !!m_ptr; }
 
+    bool is_null() const { return !m_ptr; }
+
 private:
     T* m_ptr = nullptr;
 };

AK/Vector.h

@@ -75,6 +75,13 @@ public:
         other.m_impl = nullptr;
     }
 
+    Vector(const Vector& other)
+    {
+        ensureCapacity(other.size());
+        for (size_t i = 0; i < other.size(); ++i)
+            unchecked_append(other[i]);
+    }
+
     Vector& operator=(Vector&& other)
     {
         if (this != &other) {
@@ -140,16 +147,22 @@ public:
         Vector<T> tmp = move(other);
         ensureCapacity(size() + tmp.size());
         for (auto&& v : tmp) {
-            uncheckedAppend(move(v));
+            unchecked_append(move(v));
         }
     }
 
-    void uncheckedAppend(T&& value)
+    void unchecked_append(T&& value)
     {
         new (m_impl->slot(m_impl->m_size)) T(move(value));
         ++m_impl->m_size;
     }
 
+    void unchecked_append(const T& value)
+    {
+        new (m_impl->slot(m_impl->m_size)) T(value);
+        ++m_impl->m_size;
+    }
+
     void append(T&& value)
     {
         ensureCapacity(size() + 1);

Kernel/MemoryManager.cpp

@@ -45,12 +45,12 @@ void MemoryManager::release_page_directory(PageDirectory& page_directory)
     dbgprintf("MM: release_page_directory for PD K%x\n", &page_directory);
 #endif
     for (size_t i = 0; i < 1024; ++i) {
-        auto page_table = page_directory.physical_addresses[i];
+        auto& page_table = page_directory.physical_pages[i];
         if (!page_table.is_null()) {
 #ifdef MM_DEBUG
-            dbgprintf("MM: deallocating process page table [%u] P%x @ %p\n", i, page_table.get(), &process.m_page_directory->physical_addresses[i]);
+            dbgprintf("MM: deallocating user page table P%x\n", page_table->paddr().get());
 #endif
-            deallocate_page_table(page_table);
+            deallocate_page_table(page_directory, i);
         }
     }
 #ifdef SCRUB_DEALLOCATED_PAGE_TABLES
@@ -76,9 +76,9 @@ void MemoryManager::initializePaging()
     // The bottom 4 MB are identity mapped & supervisor only. Every process shares these mappings.
     create_identity_mapping(LinearAddress(PAGE_SIZE), 4 * MB);
  
-    // The physical pages 4 MB through 8 MB are available for Zone allocation.
+    // The physical pages 4 MB through 8 MB are available for allocation.
     for (size_t i = (4 * MB) + PAGE_SIZE; i < (8 * MB); i += PAGE_SIZE)
-        m_freePages.append(PhysicalAddress(i));
+        m_free_physical_pages.append(adopt(*new PhysicalPage(PhysicalAddress(i))));
 
     asm volatile("movl %%eax, %%cr3"::"a"(m_kernel_page_directory));
     asm volatile(
@@ -88,20 +88,29 @@ void MemoryManager::initializePaging()
     );
 }
 
-PhysicalAddress MemoryManager::allocate_page_table()
+RetainPtr<PhysicalPage> MemoryManager::allocate_page_table(PageDirectory& page_directory, unsigned index)
 {
-    auto ppages = allocatePhysicalPages(1);
-    dword address = ppages[0].get();
+    auto& page_directory_physical_ptr = page_directory.physical_pages[index];
+    ASSERT(!page_directory_physical_ptr);
+    auto ppages = allocate_physical_pages(1);
+    ASSERT(ppages.size() == 1);
+    dword address = ppages[0]->paddr().get();
     create_identity_mapping(LinearAddress(address), PAGE_SIZE);
     memset((void*)address, 0, PAGE_SIZE);
-    return PhysicalAddress(address);
+    page_directory.physical_pages[index] = move(ppages[0]);
+    return page_directory.physical_pages[index];
 }
 
-void MemoryManager::deallocate_page_table(PhysicalAddress paddr)
+void MemoryManager::deallocate_page_table(PageDirectory& page_directory, unsigned index)
 {
-    ASSERT(!m_freePages.contains_slow(paddr));
-    remove_identity_mapping(LinearAddress(paddr.get()), PAGE_SIZE);
-    m_freePages.append(paddr);
+    auto& physical_page = page_directory.physical_pages[index];
+    ASSERT(physical_page);
+    ASSERT(!m_free_physical_pages.contains_slow(physical_page));
+    for (size_t i = 0; i < MM.m_free_physical_pages.size(); ++i) {
+        ASSERT(MM.m_free_physical_pages[i].ptr() != physical_page.ptr());
+    }
+    remove_identity_mapping(LinearAddress(physical_page->paddr().get()), PAGE_SIZE);
+    page_directory.physical_pages[index] = nullptr;
 }
 
 void MemoryManager::remove_identity_mapping(LinearAddress laddr, size_t size)
@@ -143,20 +152,21 @@ auto MemoryManager::ensurePTE(PageDirectory* page_directory, LinearAddress laddr
             pde.setPresent(true);
             pde.setWritable(true);
         } else {
-            auto page_table = allocate_page_table();
+            auto page_table = allocate_page_table(*page_directory, page_directory_index);
 #ifdef MM_DEBUG
             dbgprintf("MM: PD K%x (%s) allocated page table #%u (for L%x) at P%x\n",
                 page_directory,
                 page_directory == m_kernel_page_directory ? "Kernel" : "User",
                 page_directory_index,
                 laddr.get(),
-                page_table);
+                page_table->paddr().get());
 #endif
-            page_directory->physical_addresses[page_directory_index] = page_table;
-            pde.setPageTableBase(page_table.get());
+
+            pde.setPageTableBase(page_table->paddr().get());
             pde.setUserAllowed(true);
             pde.setPresent(true);
             pde.setWritable(true);
+            page_directory->physical_pages[page_directory_index] = move(page_table);
         }
     }
     return PageTableEntry(&pde.pageTableBase()[page_table_index]);
@@ -209,61 +219,18 @@ PageFaultResponse MemoryManager::handlePageFault(const PageFault& fault)
     return PageFaultResponse::ShouldCrash;
 }
 
-void MemoryManager::registerZone(Zone& zone)
-{
-    ASSERT_INTERRUPTS_DISABLED();
-    m_zones.set(&zone);
-#ifdef MM_DEBUG
-    for (size_t i = 0; i < zone.m_pages.size(); ++i)
-        dbgprintf("MM: allocated to zone: P%x\n", zone.m_pages[i].get());
-#endif
-}
-
-void MemoryManager::unregisterZone(Zone& zone)
-{
-    ASSERT_INTERRUPTS_DISABLED();
-#ifdef MM_DEBUG
-    for (size_t i = 0; i < zone.m_pages.size(); ++i)
-        dbgprintf("MM: deallocated from zone: P%x\n", zone.m_pages[i].get());
-#endif
-    m_zones.remove(&zone);
-    m_freePages.append(move(zone.m_pages));
-}
-
-Zone::Zone(Vector<PhysicalAddress>&& pages)
-    : m_pages(move(pages))
-{
-    MM.registerZone(*this);
-}
-
-Zone::~Zone()
-{
-    MM.unregisterZone(*this);
-}
-
-RetainPtr<Zone> MemoryManager::createZone(size_t size)
-{
-    InterruptDisabler disabler;
-    auto pages = allocatePhysicalPages(ceilDiv(size, PAGE_SIZE));
-    if (pages.isEmpty()) {
-        kprintf("MM: createZone: no physical pages for size %u\n", size);
-        return nullptr;
-    }
-    return adopt(*new Zone(move(pages)));
-}
-
-Vector<PhysicalAddress> MemoryManager::allocatePhysicalPages(size_t count)
+Vector<RetainPtr<PhysicalPage>> MemoryManager::allocate_physical_pages(size_t count)
 {
     InterruptDisabler disabler;
-    if (count > m_freePages.size())
+    if (count > m_free_physical_pages.size())
         return { };
 
-    Vector<PhysicalAddress> pages;
+    Vector<RetainPtr<PhysicalPage>> pages;
     pages.ensureCapacity(count);
     for (size_t i = 0; i < count; ++i) {
-        pages.append(m_freePages.takeLast());
+        pages.append(m_free_physical_pages.takeLast());
 #ifdef MM_DEBUG
-        dbgprintf("MM: allocate_physical_pages vending P%x\n", pages.last());
+        dbgprintf("MM: allocate_physical_pages vending P%x\n", pages.last()->paddr().get());
 #endif
     }
     return pages;
@@ -299,17 +266,22 @@ void MemoryManager::flushTLB(LinearAddress laddr)
 void MemoryManager::map_region_at_address(PageDirectory* page_directory, Region& region, LinearAddress laddr, bool user_allowed)
 {
     InterruptDisabler disabler;
-    auto& zone = *region.zone;
-    for (size_t i = 0; i < zone.m_pages.size(); ++i) {
+    for (size_t i = 0; i < region.physical_pages.size(); ++i) {
         auto page_laddr = laddr.offset(i * PAGE_SIZE);
         auto pte = ensurePTE(page_directory, page_laddr);
-        pte.setPhysicalPageBase(zone.m_pages[i].get());
-        pte.setPresent(true); // FIXME: Maybe we could use the is_readable flag here?
+        auto& physical_page = region.physical_pages[i];
+        if (physical_page) {
+            pte.setPhysicalPageBase(physical_page->paddr().get());
+            pte.setPresent(true); // FIXME: Maybe we should use the is_readable flag here?
+        } else {
+            pte.setPhysicalPageBase(0);
+            pte.setPresent(false);
+        }
         pte.setWritable(region.is_writable);
         pte.setUserAllowed(user_allowed);
         flushTLB(page_laddr);
 #ifdef MM_DEBUG
-        dbgprintf("MM: >> map_region_at_address (PD=%x) L%x => P%x\n", page_directory, page_laddr, zone.m_pages[i].get());
+        dbgprintf("MM: >> map_region_at_address (PD=%x) '%s' L%x => P%x (@%p)\n", page_directory, region.name.characters(), page_laddr, physical_page ? physical_page->paddr().get() : 0, physical_page.ptr());
 #endif
     }
 }
@@ -369,8 +341,7 @@ void MemoryManager::remove_kernel_alias_for_region(Region& region, byte* addr)
 bool MemoryManager::unmapRegion(Process& process, Region& region)
 {
     InterruptDisabler disabler;
-    auto& zone = *region.zone;
-    for (size_t i = 0; i < zone.m_pages.size(); ++i) {
+    for (size_t i = 0; i < region.physical_pages.size(); ++i) {
         auto laddr = region.linearAddress.offset(i * PAGE_SIZE);
         auto pte = ensurePTE(process.m_page_directory, laddr);
         pte.setPhysicalPageBase(0);
@@ -379,7 +350,8 @@ bool MemoryManager::unmapRegion(Process& process, Region& region)
         pte.setUserAllowed(false);
         flushTLB(laddr);
 #ifdef MM_DEBUG
-        //dbgprintf("MM: >> Unmapped L%x => P%x <<\n", laddr, zone.m_pages[i].get());
+        auto& physical_page = region.physical_pages[i];
+        dbgprintf("MM: >> Unmapped L%x => P%x <<\n", laddr, physical_page ? physical_page->paddr().get() : 0);
 #endif
     }
     return true;
@@ -429,12 +401,12 @@ RetainPtr<Region> Region::clone()
     KernelPagingScope pagingScope;
 
     if (is_readable && !is_writable) {
-        // Create a new region backed by the same zone.
-        return adopt(*new Region(linearAddress, size, zone.copyRef(), String(name), is_readable, is_writable));
+        // Create a new region backed by the same physical pages.
+        return adopt(*new Region(linearAddress, size, physical_pages, String(name), is_readable, is_writable));
     }
     // FIXME: Implement COW regions.
-    auto clone_zone = MM.createZone(zone->size());
-    auto clone_region = adopt(*new Region(linearAddress, size, move(clone_zone), String(name), is_readable, is_writable));
+    auto clone_physical_pages = MM.allocate_physical_pages(physical_pages.size());
+    auto clone_region = adopt(*new Region(linearAddress, size, move(clone_physical_pages), String(name), is_readable, is_writable));
 
     // FIXME: It would be cool to make the src_alias a read-only mapping.
     byte* src_alias = MM.create_kernel_alias_for_region(*this);
@@ -447,3 +419,26 @@ RetainPtr<Region> Region::clone()
     return clone_region;
 }
 
+Region::Region(LinearAddress a, size_t s, Vector<RetainPtr<PhysicalPage>> pp, String&& n, bool r, bool w)
+    : linearAddress(a)
+    , size(s)
+    , physical_pages(move(pp))
+    , name(move(n))
+    , is_readable(r)
+    , is_writable(w)
+{
+}
+
+Region::~Region()
+{
+}
+
+void PhysicalPage::return_to_freelist()
+{
+    InterruptDisabler disabler;
+    m_retain_count = 1;
+    MM.m_free_physical_pages.append(adopt(*this));
+#ifdef MM_DEBUG
+    dbgprintf("MM: P%x released to freelist\n", m_paddr.get());
+#endif
+}

Kernel/MemoryManager.h

@@ -17,34 +17,50 @@ enum class PageFaultResponse {
     Continue,
 };
 
-struct PageDirectory {
-    dword entries[1024];
-    PhysicalAddress physical_addresses[1024];
-};
-
-struct Zone : public Retainable<Zone> {
-    friend ByteBuffer procfs$mm();
+class PhysicalPage {
+    friend class MemoryManager;
 public:
-    ~Zone();
-    size_t size() const { return m_pages.size() * PAGE_SIZE; }
-
-    const Vector<PhysicalAddress>& pages() const { return m_pages; }
+    ~PhysicalPage() { }
+    PhysicalAddress paddr() const { return m_paddr; }
+
+    void retain()
+    {
+        ASSERT(m_retain_count);
+        ++m_retain_count;
+    }
+
+    void release()
+    {
+        ASSERT(m_retain_count);
+        if (!--m_retain_count)
+            return_to_freelist();
+    }
 
 private:
-    friend class MemoryManager;
-    explicit Zone(Vector<PhysicalAddress>&&);
+    PhysicalPage(PhysicalAddress paddr)
+        : m_paddr(paddr)
+    {
+    }
+
+    void return_to_freelist();
 
-    Vector<PhysicalAddress> m_pages;
+    unsigned m_retain_count { 1 };
+    PhysicalAddress m_paddr;
+};
+
+struct PageDirectory {
+    dword entries[1024];
+    RetainPtr<PhysicalPage> physical_pages[1024];
 };
 
 struct Region : public Retainable<Region> {
-    Region(LinearAddress, size_t, RetainPtr<Zone>&&, String&&, bool r, bool w);
+    Region(LinearAddress, size_t, Vector<RetainPtr<PhysicalPage>>, String&&, bool r, bool w);
     ~Region();
 
     RetainPtr<Region> clone();
     LinearAddress linearAddress;
     size_t size { 0 };
-    RetainPtr<Zone> zone;
+    Vector<RetainPtr<PhysicalPage>> physical_pages;
     String name;
     bool is_readable { true };
     bool is_writable { true };
@@ -54,6 +70,7 @@ struct Region : public Retainable<Region> {
 
 class MemoryManager {
     AK_MAKE_ETERNAL
+    friend class PhysicalPage;
     friend ByteBuffer procfs$mm();
 public:
     static MemoryManager& the() PURE;
@@ -64,14 +81,9 @@ public:
 
     PageFaultResponse handlePageFault(const PageFault&);
 
-    RetainPtr<Zone> createZone(size_t);
-
     bool mapRegion(Process&, Region&);
     bool unmapRegion(Process&, Region&);
 
-    void registerZone(Zone&);
-    void unregisterZone(Zone&);
-
     void populate_page_directory(PageDirectory&);
     void release_page_directory(PageDirectory&);
 
@@ -84,6 +96,8 @@ public:
     bool validate_user_read(const Process&, LinearAddress) const;
     bool validate_user_write(const Process&, LinearAddress) const;
 
+    Vector<RetainPtr<PhysicalPage>> allocate_physical_pages(size_t count);
+
 private:
     MemoryManager();
     ~MemoryManager();
@@ -96,16 +110,14 @@ private:
     void flushEntireTLB();
     void flushTLB(LinearAddress);
 
-    PhysicalAddress allocate_page_table();
-    void deallocate_page_table(PhysicalAddress);
+    RetainPtr<PhysicalPage> allocate_page_table(PageDirectory&, unsigned index);
+    void deallocate_page_table(PageDirectory&, unsigned index);
 
     void protectMap(LinearAddress, size_t length);
 
     void create_identity_mapping(LinearAddress, size_t length);
     void remove_identity_mapping(LinearAddress, size_t);
 
-    Vector<PhysicalAddress> allocatePhysicalPages(size_t count);
-
     struct PageDirectoryEntry {
         explicit PageDirectoryEntry(dword* pde) : m_pde(pde) { }
 
@@ -192,9 +204,7 @@ private:
 
     LinearAddress m_next_laddr;
 
-    HashTable<Zone*> m_zones;
-
-    Vector<PhysicalAddress> m_freePages;
+    Vector<RetainPtr<PhysicalPage>> m_free_physical_pages;
 };
 
 struct KernelPagingScope {

Kernel/ProcFileSystem.cpp

@@ -49,7 +49,7 @@ ByteBuffer procfs$pid_vm(Process& process)
 {
     ProcessInspectionScope scope(process);
     char* buffer;
-    auto stringImpl = StringImpl::createUninitialized(80 + process.regionCount() * 80, buffer);
+    auto stringImpl = StringImpl::createUninitialized(80 + process.regionCount() * 80 + 4096, buffer);
     memset(buffer, 0, stringImpl->length());
     char* ptr = buffer;
     ptr += ksprintf(ptr, "BEGIN       END         SIZE        NAME\n");
@@ -59,6 +59,10 @@ ByteBuffer procfs$pid_vm(Process& process)
             region->linearAddress.offset(region->size - 1).get(),
             region->size,
             region->name.characters());
+        for (auto& physical_page : region->physical_pages) {
+            ptr += ksprintf(ptr, "P%x ", physical_page ? physical_page->paddr().get() : 0);
+        }
+        ptr += ksprintf(ptr, "\n");
     }
     *ptr = '\0';
     return ByteBuffer::copy((byte*)buffer, ptr - buffer);
@@ -130,6 +134,8 @@ void ProcFileSystem::removeProcess(Process& process)
 
 ByteBuffer procfs$mm()
 {
+    // FIXME: Implement
+#if 0
     InterruptDisabler disabler;
     size_t zonePageCount = 0;
     for (auto* zone : MM.m_zones)
@@ -143,9 +149,11 @@ ByteBuffer procfs$mm()
         ptr += ksprintf(ptr, "\n");
     }
     ptr += ksprintf(ptr, "Zone count: %u\n", MM.m_zones.size());
-    ptr += ksprintf(ptr, "Free physical pages: %u\n", MM.m_freePages.size());
+    ptr += ksprintf(ptr, "Free physical pages: %u\n", MM.m_free_physical_pages.size());
     buffer.trim(ptr - (char*)buffer.pointer());
     return buffer;
+#endif
+    return { };
 }
 
 

Kernel/Process.cpp

@@ -17,6 +17,7 @@
 
 //#define DEBUG_IO
 //#define TASK_DEBUG
+//#define FORK_DEBUG
 //#define SCHEDULER_DEBUG
 
 // FIXME: Only do a single validation for accesses that don't span multiple pages.
@@ -144,11 +145,11 @@ Region* Process::allocate_region(LinearAddress laddr, size_t size, String&& name
 
     laddr.mask(0xfffff000);
 
-    auto zone = MM.createZone(size);
-    ASSERT(zone);
-
-    m_regions.append(adopt(*new Region(laddr, size, move(zone), move(name), is_readable, is_writable)));
+    unsigned page_count = ceilDiv(size, PAGE_SIZE);
+    auto physical_pages = MM.allocate_physical_pages(page_count);
+    ASSERT(physical_pages.size() == page_count);
 
+    m_regions.append(adopt(*new Region(laddr, size, move(physical_pages), move(name), is_readable, is_writable)));
     MM.mapRegion(*this, *m_regions.last());
     return m_regions.last().ptr();
 }
@@ -1258,20 +1259,6 @@ Process* Process::kernelProcess()
     return s_kernelProcess;
 }
 
-Region::Region(LinearAddress a, size_t s, RetainPtr<Zone>&& z, String&& n, bool r, bool w)
-    : linearAddress(a)
-    , size(s)
-    , zone(move(z))
-    , name(move(n))
-    , is_readable(r)
-    , is_writable(w)
-{
-}
-
-Region::~Region()
-{
-}
-
 bool Process::isValidAddressForKernel(LinearAddress laddr) const
 {
     // We check extra carefully here since the first 4MB of the address space is identity-mapped.

Kernel/i386.cpp

@@ -318,7 +318,7 @@ void gdt_init()
     s_gdt_freelist = new Vector<word, KmallocEternalAllocator>();
     s_gdt_freelist->ensureCapacity(256);
     for (size_t i = s_gdtLength; i < 256; ++i)
-        s_gdt_freelist->uncheckedAppend(i * 8);
+        s_gdt_freelist->unchecked_append(i * 8);
 
     s_gdtLength = 256;
     s_gdtr.address = s_gdt;

Kernel/sync.sh

@@ -19,6 +19,7 @@ cp ../Userland/uname mnt/bin/uname
 cp ../Userland/clear mnt/bin/clear
 cp ../Userland/tst mnt/bin/tst
 cp ../Userland/ft mnt/bin/ft
+cp ../Userland/ft2 mnt/bin/ft2
 cp ../Userland/mm mnt/bin/mm
 cp ../Userland/kill mnt/bin/kill
 cp ../Userland/tty mnt/bin/tty

Userland/.gitignore

@@ -17,3 +17,4 @@ mm
 kill
 tty
 ft
+ft2

Userland/ft2.cpp

@@ -0,0 +1,16 @@
+#include <stdio.h>
+#include <unistd.h>
+
+int main(int argc, char** argv)
+{
+    printf("Testing fork()...\n");
+    pid_t pid = fork();
+    if (!pid) {
+        printf("child, pid=%d\n", getpid());
+        for (;;);
+    } else {
+        printf("parent, child pid=%d\n", pid);
+        for (;;);
+    }
+    return 0;
+}