LibDraw: Add GraphicsBitmap::create_purgeable()

This allows you to create a process-private purgeable GraphicsBitmap.
The volatile flag is controlled via set_volatile() / set_nonvolatile().

Libraries/LibDraw/GraphicsBitmap.cpp

@@ -9,17 +9,24 @@
 
 NonnullRefPtr<GraphicsBitmap> GraphicsBitmap::create(Format format, const Size& size)
 {
-    return adopt(*new GraphicsBitmap(format, size));
+    return adopt(*new GraphicsBitmap(format, size, Purgeable::No));
 }
 
-GraphicsBitmap::GraphicsBitmap(Format format, const Size& size)
+NonnullRefPtr<GraphicsBitmap> GraphicsBitmap::create_purgeable(Format format, const Size& size)
+{
+    return adopt(*new GraphicsBitmap(format, size, Purgeable::Yes));
+}
+
+GraphicsBitmap::GraphicsBitmap(Format format, const Size& size, Purgeable purgeable)
     : m_size(size)
     , m_pitch(round_up_to_power_of_two(size.width() * sizeof(RGBA32), 16))
     , m_format(format)
+    , m_purgeable(purgeable == Purgeable::Yes)
 {
     if (format == Format::Indexed8)
         m_palette = new RGBA32[256];
-    m_data = (RGBA32*)mmap_with_name(nullptr, size_in_bytes(), PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, 0, 0, String::format("GraphicsBitmap [%dx%d]", width(), height()).characters());
+    int map_flags = purgeable == Purgeable::Yes ? (MAP_PURGEABLE | MAP_PRIVATE) : (MAP_ANONYMOUS | MAP_PRIVATE);
+    m_data = (RGBA32*)mmap_with_name(nullptr, size_in_bytes(), PROT_READ | PROT_WRITE, map_flags, 0, 0, String::format("GraphicsBitmap [%dx%d]", width(), height()).characters());
     ASSERT(m_data && m_data != (void*)-1);
     m_needs_munmap = true;
 }
@@ -111,3 +118,30 @@ void GraphicsBitmap::fill(Color color)
         fast_u32_fill(scanline, color.value(), width());
     }
 }
+
+void GraphicsBitmap::set_volatile()
+{
+    ASSERT(m_purgeable);
+    if (m_volatile)
+        return;
+    int rc = madvise(m_data, size_in_bytes(), MADV_SET_VOLATILE);
+    if (rc < 0) {
+        perror("madvise(MADV_SET_VOLATILE)");
+        ASSERT_NOT_REACHED();
+    }
+    m_volatile = true;
+}
+
+[[nodiscard]] bool GraphicsBitmap::set_nonvolatile()
+{
+    ASSERT(m_purgeable);
+    if (!m_volatile)
+        return true;
+    int rc = madvise(m_data, size_in_bytes(), MADV_SET_NONVOLATILE);
+    if (rc < 0) {
+        perror("madvise(MADV_SET_NONVOLATILE)");
+        ASSERT_NOT_REACHED();
+    }
+    m_volatile = false;
+    return rc == 0;
+}

Libraries/LibDraw/GraphicsBitmap.h

@@ -20,6 +20,7 @@ public:
     };
 
     static NonnullRefPtr<GraphicsBitmap> create(Format, const Size&);
+    static NonnullRefPtr<GraphicsBitmap> create_purgeable(Format, const Size&);
     static NonnullRefPtr<GraphicsBitmap> create_wrapper(Format, const Size&, size_t pitch, RGBA32*);
     static RefPtr<GraphicsBitmap> load_from_file(const StringView& path);
     static RefPtr<GraphicsBitmap> load_from_file(Format, const StringView& path, const Size&);
@@ -98,8 +99,14 @@ public:
         set_pixel(position.x(), position.y(), color);
     }
 
+    bool is_purgeable() const { return m_purgeable; }
+    bool is_volatile() const { return m_volatile; }
+    void set_volatile();
+    [[nodiscard]] bool set_nonvolatile();
+
 private:
-    GraphicsBitmap(Format, const Size&);
+    enum class Purgeable { No, Yes };
+    GraphicsBitmap(Format, const Size&, Purgeable);
     GraphicsBitmap(Format, const Size&, size_t pitch, RGBA32*);
     GraphicsBitmap(Format, const Size&, MappedFile&&);
     GraphicsBitmap(Format, NonnullRefPtr<SharedBuffer>&&, const Size&);
@@ -110,6 +117,8 @@ private:
     size_t m_pitch { 0 };
     Format m_format { Format::Invalid };
     bool m_needs_munmap { false };
+    bool m_purgeable { false };
+    bool m_volatile { false };
     MappedFile m_mapped_file;
     RefPtr<SharedBuffer> m_shared_buffer;
 };