Kernel: Remove MAP_PURGEABLE from mmap

This brings mmap more in line with other operating systems. Prior to
this, it was impossible to request memory that was definitely committed,
instead MAP_PURGEABLE would provide a region that was not actually
purgeable, but also not fully committed, which meant that using such memory
still could cause crashes when the underlying pages could no longer be
allocated.

This fixes some random crashes in low-memory situations where non-volatile
memory is mapped (e.g. malloc, tls, Gfx::Bitmap, etc) but when a page in
these regions is first accessed, there is insufficient physical memory
available to commit a new page.

Kernel/Process.cpp

@@ -144,7 +144,7 @@ Region& Process::allocate_split_region(const Region& source_region, const Range&
 Region* Process::allocate_region(const Range& range, const String& name, int prot, bool should_commit)
 {
     ASSERT(range.is_valid());
-    auto vmobject = AnonymousVMObject::create_with_size(range.size());
+    auto vmobject = PurgeableVMObject::create_with_size(range.size());
     auto region = Region::create_user_accessible(this, range, vmobject, 0, name, prot_to_region_access_flags(prot));
     if (!region->map(page_directory()))
         return nullptr;

Kernel/Syscalls/mmap.cpp

@@ -116,7 +116,6 @@ void* Process::sys$mmap(Userspace<const Syscall::SC_mmap_params*> user_params)
 
     bool map_shared = flags & MAP_SHARED;
     bool map_anonymous = flags & MAP_ANONYMOUS;
-    bool map_purgeable = flags & MAP_PURGEABLE;
     bool map_private = flags & MAP_PRIVATE;
     bool map_stack = flags & MAP_STACK;
     bool map_fixed = flags & MAP_FIXED;
@@ -136,19 +135,13 @@ void* Process::sys$mmap(Userspace<const Syscall::SC_mmap_params*> user_params)
 
     Region* region = nullptr;
     Optional<Range> range;
-    if (map_purgeable || map_anonymous) {
+    if (map_noreserve || map_anonymous) {
         range = allocate_range(VirtualAddress(addr), size, alignment);
         if (!range.value().is_valid())
             return (void*)-ENOMEM;
     }
 
-    if (map_purgeable) {
-
-        auto vmobject = PurgeableVMObject::create_with_size(size);
-        region = allocate_region_with_vmobject(range.value(), vmobject, 0, !name.is_null() ? name : "mmap (purgeable)", prot);
-        if (!region && (!map_fixed && addr != 0))
-            region = allocate_region_with_vmobject({}, size, vmobject, 0, !name.is_null() ? name : "mmap (purgeable)", prot);
-    } else if (map_anonymous) {
+    if (map_anonymous) {
         region = allocate_region(range.value(), !name.is_null() ? name : "mmap", prot, !map_noreserve);
         if (!region && (!map_fixed && addr != 0))
             region = allocate_region(allocate_range({}, size), !name.is_null() ? name : "mmap", prot, !map_noreserve);
@@ -437,7 +430,7 @@ void* Process::sys$mremap(Userspace<const Syscall::SC_mremap_params*> user_param
     if (!old_region->is_mmap())
         return (void*)-EPERM;
 
-    if (old_region->vmobject().is_shared_inode() && params.flags & MAP_PRIVATE && !(params.flags & MAP_ANONYMOUS) && !(params.flags & MAP_PURGEABLE)) {
+    if (old_region->vmobject().is_shared_inode() && params.flags & MAP_PRIVATE && !(params.flags & (MAP_ANONYMOUS | MAP_NORESERVE))) {
         auto range = old_region->range();
         auto old_name = old_region->name();
         auto old_prot = region_access_flags_to_prot(old_region->access());

Kernel/UnixTypes.h

@@ -92,8 +92,7 @@ enum {
 #define MAP_ANONYMOUS 0x20
 #define MAP_ANON MAP_ANONYMOUS
 #define MAP_STACK 0x40
-#define MAP_PURGEABLE 0x80
-#define MAP_NORESERVE 0x100
+#define MAP_NORESERVE 0x80
 
 #define PROT_READ 0x1
 #define PROT_WRITE 0x2

Libraries/LibC/malloc.cpp

@@ -154,7 +154,7 @@ extern "C" {
 
 static void* os_alloc(size_t size, const char* name)
 {
-    auto* ptr = serenity_mmap(nullptr, size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE | MAP_PURGEABLE, 0, 0, ChunkedBlock::block_size, name);
+    auto* ptr = serenity_mmap(nullptr, size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, 0, 0, ChunkedBlock::block_size, name);
     ASSERT(ptr != MAP_FAILED);
     return ptr;
 }

Libraries/LibC/mman.h

@@ -36,7 +36,7 @@
 #define MAP_ANONYMOUS 0x20
 #define MAP_ANON MAP_ANONYMOUS
 #define MAP_STACK 0x40
-#define MAP_PURGEABLE 0x80
+#define MAP_NORESERVE 0x80
 
 #define PROT_READ 0x1
 #define PROT_WRITE 0x2

Libraries/LibGfx/Bitmap.cpp

@@ -437,13 +437,13 @@ Optional<BackingStore> Bitmap::allocate_backing_store(BitmapFormat format, const
     const auto pitch = minimum_pitch(size.width(), format);
     const auto data_size_in_bytes = size_in_bytes(pitch, size.height());
 
-    void* data = nullptr;
+    int map_flags = MAP_ANONYMOUS | MAP_PRIVATE;
+    if (purgeable == Purgeable::Yes)
+        map_flags |= MAP_NORESERVE;
 #ifdef __serenity__
-    int map_flags = purgeable == Purgeable::Yes ? (MAP_PURGEABLE | MAP_PRIVATE) : (MAP_ANONYMOUS | MAP_PRIVATE);
-    data = mmap_with_name(nullptr, data_size_in_bytes, PROT_READ | PROT_WRITE, map_flags, 0, 0, String::format("GraphicsBitmap [%dx%d]", size.width(), size.height()).characters());
+    void* data = mmap_with_name(nullptr, data_size_in_bytes, PROT_READ | PROT_WRITE, map_flags, 0, 0, String::format("GraphicsBitmap [%dx%d]", size.width(), size.height()).characters());
 #else
-    int map_flags = (MAP_ANONYMOUS | MAP_PRIVATE);
-    data = mmap(nullptr, data_size_in_bytes, PROT_READ | PROT_WRITE, map_flags, 0, 0);
+    void* data = mmap(nullptr, data_size_in_bytes, PROT_READ | PROT_WRITE, map_flags, 0, 0);
 #endif
     if (data == MAP_FAILED) {
         perror("mmap");