Kernel: Refactor MemoryManager to use a Bitmap rather than a Vector

This significantly reduces the pressure on the kernel heap when
allocating a lot of pages.

Previously at about 250MB allocated, the free page list would outgrow
the kernel's heap. Given that there is no longer a page list, this does
not happen.

The next barrier will be the kernel memory used by the page records for
in-use memory. This kicks in at about 1GB.

Kernel/FileSystem/ProcFS.cpp

@@ -387,8 +387,8 @@ ByteBuffer procfs$mm(InodeIdentifier)
             vmo->name().characters());
     }
     builder.appendf("VMO count: %u\n", MM.m_vmos.size());
-    builder.appendf("Free physical pages: %u\n", MM.m_free_physical_pages.size());
-    builder.appendf("Free supervisor physical pages: %u\n", MM.m_free_supervisor_physical_pages.size());
+    builder.appendf("Free physical pages: %u\n", MM.user_physical_pages() - MM.user_physical_pages_used());
+    builder.appendf("Free supervisor physical pages: %u\n", MM.super_physical_pages() - MM.super_physical_pages_used());
     return builder.to_byte_buffer();
 }
 
@@ -544,10 +544,10 @@ ByteBuffer procfs$memstat(InodeIdentifier)
         kmalloc_sum_eternal,
         sum_alloc,
         sum_free,
-        MM.user_physical_pages_in_existence() - MM.m_free_physical_pages.size(),
-        MM.m_free_physical_pages.size(),
-        MM.super_physical_pages_in_existence() - MM.m_free_supervisor_physical_pages.size(),
-        MM.m_free_supervisor_physical_pages.size(),
+        MM.user_physical_pages_used(),
+        MM.user_physical_pages() - MM.user_physical_pages_used(),
+        MM.super_physical_pages_used(),
+        MM.super_physical_pages() - MM.super_physical_pages_used(),
         g_kmalloc_call_count,
         g_kfree_call_count);
     return builder.to_byte_buffer();

Kernel/Makefile

@@ -18,6 +18,7 @@ KERNEL_OBJS = \
        VM/VMObject.o \
        VM/PageDirectory.o \
        VM/PhysicalPage.o \
+       VM/PhysicalRegion.o \
        VM/RangeAllocator.o \
        Console.o \
        IRQHandler.o \

Kernel/VM/MemoryManager.cpp

@@ -12,8 +12,6 @@
 //#define PAGE_FAULT_DEBUG
 
 static MemoryManager* s_the;
-unsigned MemoryManager::s_user_physical_pages_in_existence;
-unsigned MemoryManager::s_super_physical_pages_in_existence;
 
 MemoryManager& MM
 {
@@ -78,6 +76,14 @@ void MemoryManager::initialize_paging()
     // 5 MB   -> 0xc0000000     Userspace physical pages (available for allocation!)
     // 0xc0000000-0xffffffff    Kernel-only linear address space
 
+#ifdef MM_DEBUG
+    dbgprintf("MM: Quickmap will use %p\n", m_quickmap_addr.get());
+#endif
+    m_quickmap_addr = VirtualAddress((1 * MB) - PAGE_SIZE);
+
+    RetainPtr<PhysicalRegion> region = nullptr;
+    bool region_is_super = false;
+
     for (auto* mmap = (multiboot_memory_map_t*)multiboot_info_ptr->mmap_addr; (unsigned long)mmap < multiboot_info_ptr->mmap_addr + multiboot_info_ptr->mmap_length; mmap = (multiboot_memory_map_t*)((unsigned long)mmap + mmap->size + sizeof(mmap->size))) {
         kprintf("MM: Multiboot mmap: base_addr = 0x%x%08x, length = 0x%x%08x, type = 0x%x\n",
             (dword)(mmap->addr >> 32),
@@ -88,26 +94,48 @@ void MemoryManager::initialize_paging()
 
         if (mmap->type != MULTIBOOT_MEMORY_AVAILABLE)
             continue;
+
         // FIXME: Maybe make use of stuff below the 1MB mark?
         if (mmap->addr < (1 * MB))
             continue;
 
-        for (size_t page_base = mmap->addr; page_base < (mmap->addr + mmap->len); page_base += PAGE_SIZE) {
-            if (page_base < (4 * MB)) {
-                // Skip over pages managed by kmalloc.
-                continue;
-            }
-
-            if (page_base < (5 * MB))
-                m_free_supervisor_physical_pages.append(PhysicalPage::create_eternal(PhysicalAddress(page_base), true));
-            else
-                m_free_physical_pages.append(PhysicalPage::create_eternal(PhysicalAddress(page_base), false));
-        }
-    }
-
-    m_quickmap_addr = VirtualAddress((1 * MB) - PAGE_SIZE);
 #ifdef MM_DEBUG
-    dbgprintf("MM: Quickmap will use P%x\n", m_quickmap_addr.get());
+        kprintf("MM: considering memory at %p - %p\n",
+            (dword)mmap->addr, (dword)(mmap->addr + mmap->len));
+#endif
+
+        for (size_t page_base = mmap->addr; page_base < (mmap->addr + mmap->len); page_base += PAGE_SIZE) {
+            auto addr = PhysicalAddress(page_base);
+
+            if (page_base < 4 * MB) {
+                // nothing
+            } else if (page_base >= 4 * MB && page_base < 5 * MB) {
+                if (region.is_null() || !region_is_super || region->upper().offset(PAGE_SIZE) != addr) {
+                    m_super_physical_regions.append(PhysicalRegion::create(addr, addr));
+                    region = m_super_physical_regions.last();
+                    region_is_super = true;
+                } else {
+                    region->expand(region->lower(), addr);
+                }
+            } else {
+                if (region.is_null() || region_is_super || region->upper().offset(PAGE_SIZE) != addr) {
+                    m_user_physical_regions.append(PhysicalRegion::create(addr, addr));
+                    region = m_user_physical_regions.last();
+                    region_is_super = false;
+                } else {
+                    region->expand(region->lower(), addr);
+                }
+            }
+        }
+    }
+
+    for (auto& region : m_super_physical_regions)
+        m_super_physical_pages += region->finalize_capacity();
+
+    for (auto& region : m_user_physical_regions)
+        m_user_physical_pages += region->finalize_capacity();
+
+#ifdef MM_DEBUG
     dbgprintf("MM: Installing page directory\n");
 #endif
 
@@ -282,7 +310,7 @@ bool MemoryManager::zero_page(Region& region, unsigned page_index_in_region)
         remap_region_page(region, page_index_in_region, true);
         return true;
     }
-    auto physical_page = allocate_physical_page(ShouldZeroFill::Yes);
+    auto physical_page = allocate_user_physical_page(ShouldZeroFill::Yes);
 #ifdef PAGE_FAULT_DEBUG
     dbgprintf("      >> ZERO P%x\n", physical_page->paddr().get());
 #endif
@@ -309,7 +337,7 @@ bool MemoryManager::copy_on_write(Region& region, unsigned page_index_in_region)
     dbgprintf("    >> It's a COW page and it's time to COW!\n");
 #endif
     auto physical_page_to_copy = move(vmo.physical_pages()[page_index_in_region]);
-    auto physical_page = allocate_physical_page(ShouldZeroFill::No);
+    auto physical_page = allocate_user_physical_page(ShouldZeroFill::No);
     byte* dest_ptr = quickmap_page(*physical_page);
     const byte* src_ptr = region.vaddr().offset(page_index_in_region * PAGE_SIZE).as_ptr();
 #ifdef PAGE_FAULT_DEBUG
@@ -360,7 +388,7 @@ bool MemoryManager::page_in_from_inode(Region& region, unsigned page_index_in_re
         memset(page_buffer + nread, 0, PAGE_SIZE - nread);
     }
     cli();
-    vmo_page = allocate_physical_page(ShouldZeroFill::No);
+    vmo_page = allocate_user_physical_page(ShouldZeroFill::No);
     if (vmo_page.is_null()) {
         kprintf("MM: page_in_from_inode was unable to allocate a physical page\n");
         return false;
@@ -430,40 +458,114 @@ RetainPtr<Region> MemoryManager::allocate_kernel_region(size_t size, String&& na
     return region;
 }
 
-RetainPtr<PhysicalPage> MemoryManager::allocate_physical_page(ShouldZeroFill should_zero_fill)
+void MemoryManager::deallocate_user_physical_page(PhysicalPage& page)
+{
+    for (auto& region : m_user_physical_regions) {
+        if (!region->contains(page)) {
+            kprintf(
+                "MM: deallocate_user_physical_page: %p not in %p -> %p\n",
+                page.paddr(), region->lower().get(), region->upper().get());
+            continue;
+        }
+
+        region->return_page(page);
+        m_user_physical_pages_used--;
+
+        return;
+    }
+
+    kprintf("MM: deallocate_user_physical_page couldn't figure out region for user page @ %p\n", page.paddr());
+    ASSERT_NOT_REACHED();
+}
+
+RetainPtr<PhysicalPage> MemoryManager::allocate_user_physical_page(ShouldZeroFill should_zero_fill)
 {
     InterruptDisabler disabler;
-    if (1 > m_free_physical_pages.size()) {
-        kprintf("FUCK! No physical pages available.\n");
+
+    RetainPtr<PhysicalPage> page = nullptr;
+
+    for (auto& region : m_user_physical_regions) {
+        page = region->take_free_page(false);
+        if (page.is_null())
+            continue;
+    }
+
+    if (!page) {
+        if (m_user_physical_regions.is_empty()) {
+            kprintf("MM: no user physical regions available (?)\n");
+        }
+
+        kprintf("MM: no user physical pages available\n");
         ASSERT_NOT_REACHED();
         return {};
     }
+
 #ifdef MM_DEBUG
-    dbgprintf("MM: allocate_physical_page vending P%x (%u remaining)\n", m_free_physical_pages.last()->paddr().get(), m_free_physical_pages.size());
+    dbgprintf("MM: allocate_user_physical_page vending P%p\n", page->paddr().get());
 #endif
-    auto physical_page = m_free_physical_pages.take_last();
+
     if (should_zero_fill == ShouldZeroFill::Yes) {
-        auto* ptr = (dword*)quickmap_page(*physical_page);
+        auto* ptr = (dword*)quickmap_page(*page);
         fast_dword_fill(ptr, 0, PAGE_SIZE / sizeof(dword));
         unquickmap_page();
     }
-    return physical_page;
+
+    m_user_physical_pages_used++;
+
+    return page;
+}
+
+void MemoryManager::deallocate_supervisor_physical_page(PhysicalPage& page)
+{
+    for (auto& region : m_super_physical_regions) {
+        if (!region->contains(page)) {
+            kprintf(
+                "MM: deallocate_supervisor_physical_page: %p not in %p -> %p\n",
+                page.paddr(), region->lower().get(), region->upper().get());
+            continue;
+        }
+
+        region->return_page(page);
+        m_super_physical_pages_used--;
+
+        return;
+    }
+
+    kprintf("MM: deallocate_supervisor_physical_page couldn't figure out region for super page @ %p\n", page.paddr());
+    ASSERT_NOT_REACHED();
 }
 
 RetainPtr<PhysicalPage> MemoryManager::allocate_supervisor_physical_page()
 {
     InterruptDisabler disabler;
-    if (1 > m_free_supervisor_physical_pages.size()) {
-        kprintf("FUCK! No physical pages available.\n");
+
+    RetainPtr<PhysicalPage> page = nullptr;
+
+    for (auto& region : m_super_physical_regions) {
+        page = region->take_free_page(true);
+        if (page.is_null())
+            continue;
+    }
+
+    if (!page) {
+        if (m_super_physical_regions.is_empty()) {
+            kprintf("MM: no super physical regions available (?)\n");
+        }
+
+        kprintf("MM: no super physical pages available\n");
         ASSERT_NOT_REACHED();
         return {};
     }
+
 #ifdef MM_DEBUG
-    dbgprintf("MM: allocate_supervisor_physical_page vending P%x (%u remaining)\n", m_free_supervisor_physical_pages.last()->paddr().get(), m_free_supervisor_physical_pages.size());
+    dbgprintf("MM: allocate_supervisor_physical_page vending P%p\n", page->paddr().get());
 #endif
-    auto physical_page = m_free_supervisor_physical_pages.take_last();
-    fast_dword_fill((dword*)physical_page->paddr().as_ptr(), 0, PAGE_SIZE / sizeof(dword));
-    return physical_page;
+
+    fast_dword_fill((dword*)page->paddr().as_ptr(), 0, PAGE_SIZE / sizeof(dword));
+
+    m_super_physical_pages_used++;
+
+    return page;
 }
 
 void MemoryManager::enter_process_paging_scope(Process& process)

Kernel/VM/MemoryManager.h

@@ -13,6 +13,7 @@
 #include <Kernel/Arch/i386/CPU.h>
 #include <Kernel/FileSystem/InodeIdentifier.h>
 #include <Kernel/VM/PhysicalPage.h>
+#include <Kernel/VM/PhysicalRegion.h>
 #include <Kernel/VM/Region.h>
 #include <Kernel/VM/VMObject.h>
 #include <Kernel/VirtualAddress.h>
@@ -32,6 +33,7 @@ class MemoryManager {
     AK_MAKE_ETERNAL
     friend class PageDirectory;
     friend class PhysicalPage;
+    friend class PhysicalRegion;
     friend class Region;
     friend class VMObject;
     friend ByteBuffer procfs$mm(InodeIdentifier);
@@ -59,19 +61,23 @@ public:
         Yes
     };
 
-    RetainPtr<PhysicalPage> allocate_physical_page(ShouldZeroFill);
+    RetainPtr<PhysicalPage> allocate_user_physical_page(ShouldZeroFill);
     RetainPtr<PhysicalPage> allocate_supervisor_physical_page();
+    void deallocate_user_physical_page(PhysicalPage&);
+    void deallocate_supervisor_physical_page(PhysicalPage&);
 
     void remap_region(PageDirectory&, Region&);
 
-    int user_physical_pages_in_existence() const { return s_user_physical_pages_in_existence; }
-    int super_physical_pages_in_existence() const { return s_super_physical_pages_in_existence; }
-
     void map_for_kernel(VirtualAddress, PhysicalAddress);
 
     RetainPtr<Region> allocate_kernel_region(size_t, String&& name);
     void map_region_at_address(PageDirectory&, Region&, VirtualAddress, bool user_accessible);
 
+    unsigned user_physical_pages() const { return m_user_physical_pages; }
+    unsigned user_physical_pages_used() const { return m_user_physical_pages_used; }
+    unsigned super_physical_pages() const { return m_super_physical_pages; }
+    unsigned super_physical_pages_used() const { return m_super_physical_pages_used; }
+
 private:
     MemoryManager();
     ~MemoryManager();
@@ -206,9 +212,6 @@ private:
         dword* m_pte;
     };
 
-    static unsigned s_user_physical_pages_in_existence;
-    static unsigned s_super_physical_pages_in_existence;
-
     PageTableEntry ensure_pte(PageDirectory&, VirtualAddress);
 
     RetainPtr<PageDirectory> m_kernel_page_directory;
@@ -217,8 +220,13 @@ private:
 
     VirtualAddress m_quickmap_addr;
 
-    Vector<Retained<PhysicalPage>> m_free_physical_pages;
-    Vector<Retained<PhysicalPage>> m_free_supervisor_physical_pages;
+    unsigned m_user_physical_pages { 0 };
+    unsigned m_user_physical_pages_used { 0 };
+    unsigned m_super_physical_pages { 0 };
+    unsigned m_super_physical_pages_used { 0 };
+
+    Vector<Retained<PhysicalRegion>> m_user_physical_regions {};
+    Vector<Retained<PhysicalRegion>> m_super_physical_regions {};
 
     HashTable<VMObject*> m_vmos;
     HashTable<Region*> m_user_regions;

Kernel/VM/PhysicalPage.cpp

@@ -21,21 +21,21 @@ PhysicalPage::PhysicalPage(PhysicalAddress paddr, bool supervisor, bool may_retu
     , m_supervisor(supervisor)
     , m_paddr(paddr)
 {
-    if (supervisor)
-        ++MemoryManager::s_super_physical_pages_in_existence;
-    else
-        ++MemoryManager::s_user_physical_pages_in_existence;
 }
 
 void PhysicalPage::return_to_freelist()
 {
     ASSERT((paddr().get() & ~PAGE_MASK) == 0);
+
     InterruptDisabler disabler;
+
     m_retain_count = 1;
+
     if (m_supervisor)
-        MM.m_free_supervisor_physical_pages.append(adopt(*this));
+        MM.deallocate_supervisor_physical_page(*this);
     else
-        MM.m_free_physical_pages.append(adopt(*this));
+        MM.deallocate_user_physical_page(*this);
+
 #ifdef MM_DEBUG
     dbgprintf("MM: P%x released to freelist\n", m_paddr.get());
 #endif

Kernel/VM/PhysicalRegion.cpp

@@ -0,0 +1,77 @@
+#include <AK/Bitmap.h>
+#include <AK/Retained.h>
+#include <AK/RetainPtr.h>
+#include <Kernel/Assertions.h>
+#include <Kernel/PhysicalAddress.h>
+#include <Kernel/VM/PhysicalPage.h>
+#include <Kernel/VM/PhysicalRegion.h>
+
+Retained<PhysicalRegion> PhysicalRegion::create(PhysicalAddress lower, PhysicalAddress upper)
+{
+    return adopt(*new PhysicalRegion(lower, upper));
+}
+
+PhysicalRegion::PhysicalRegion(PhysicalAddress lower, PhysicalAddress upper)
+    : m_lower(lower)
+    , m_upper(upper)
+    , m_bitmap(Bitmap::create())
+{
+}
+
+void PhysicalRegion::expand(PhysicalAddress lower, PhysicalAddress upper)
+{
+    ASSERT(!m_pages);
+
+    m_lower = lower;
+    m_upper = upper;
+}
+
+unsigned PhysicalRegion::finalize_capacity()
+{
+    ASSERT(!m_pages);
+
+    m_pages = (m_upper.get() - m_lower.get()) / PAGE_SIZE;
+    m_bitmap.grow(m_pages, false);
+
+    return size();
+}
+
+RetainPtr<PhysicalPage> PhysicalRegion::take_free_page(bool supervisor)
+{
+    ASSERT(m_pages);
+
+    if (m_used == m_pages)
+        return nullptr;
+
+    for (unsigned page = m_last; page < m_pages; page++) {
+        if (!m_bitmap.get(page)) {
+            m_bitmap.set(page, true);
+            m_used++;
+            m_last = page + 1;
+            return PhysicalPage::create(m_lower.offset(page * PAGE_SIZE), supervisor);
+        }
+    }
+
+    ASSERT_NOT_REACHED();
+
+    return nullptr;
+}
+
+void PhysicalRegion::return_page_at(PhysicalAddress addr)
+{
+    ASSERT(m_pages);
+
+    if (m_used == 0) {
+        ASSERT_NOT_REACHED();
+    }
+
+    int local_offset = addr.get() - m_lower.get();
+    ASSERT(local_offset >= 0);
+    ASSERT(local_offset < m_pages * PAGE_SIZE);
+
+    auto page = local_offset / PAGE_SIZE;
+    if (page < m_last) m_last = page;
+
+    m_bitmap.set(page, false);
+    m_used--;
+}

Kernel/VM/PhysicalRegion.h

@@ -0,0 +1,39 @@
+#pragma once
+
+#include <AK/Bitmap.h>
+#include <AK/Retainable.h>
+#include <AK/Retained.h>
+#include <Kernel/PhysicalAddress.h>
+#include <Kernel/VM/PhysicalPage.h>
+
+class PhysicalRegion : public Retainable<PhysicalRegion> {
+    AK_MAKE_ETERNAL
+
+public:
+    static Retained<PhysicalRegion> create(PhysicalAddress lower, PhysicalAddress upper);
+    ~PhysicalRegion() {}
+
+    void expand(PhysicalAddress lower, PhysicalAddress upper);
+    unsigned finalize_capacity();
+
+    PhysicalAddress lower() const { return m_lower; }
+    PhysicalAddress upper() const { return m_upper; }
+    unsigned size() const { return m_pages; }
+    unsigned used() const { return m_used; }
+    unsigned free() const { return m_pages - m_used; }
+    bool contains(PhysicalPage& page) const { return page.paddr() >= m_lower && page.paddr() <= m_upper; }
+
+    RetainPtr<PhysicalPage> take_free_page(bool supervisor);
+    void return_page_at(PhysicalAddress addr);
+    void return_page(PhysicalPage& page) { return_page_at(page.paddr()); }
+
+private:
+    PhysicalRegion(PhysicalAddress lower, PhysicalAddress upper);
+
+    PhysicalAddress m_lower;
+    PhysicalAddress m_upper;
+    unsigned m_pages { 0 };
+    unsigned m_used { 0 };
+    unsigned m_last { 0 };
+    Bitmap m_bitmap;
+};

Kernel/VM/Region.cpp

@@ -103,7 +103,7 @@ int Region::commit()
     for (size_t i = first_page_index(); i <= last_page_index(); ++i) {
         if (!vmo().physical_pages()[i].is_null())
             continue;
-        auto physical_page = MM.allocate_physical_page(MemoryManager::ShouldZeroFill::Yes);
+        auto physical_page = MM.allocate_user_physical_page(MemoryManager::ShouldZeroFill::Yes);
         if (!physical_page) {
             kprintf("MM: commit was unable to allocate a physical page\n");
             return -ENOMEM;