WIP sparse stuff

src/Ryujinx.Memory/SparseMemoryBlock.cs

@@ -0,0 +1,120 @@
+using Ryujinx.Common;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Ryujinx.Memory
+{
+    public delegate void PageInitDelegate(Span<byte> page);
+
+    public class SparseMemoryBlock : IDisposable
+    {
+        private const ulong MapGranularity = 1UL << 17;
+
+        private readonly PageInitDelegate _pageInit;
+
+        private readonly object _lock = new object();
+        private readonly ulong _pageSize;
+        private readonly MemoryBlock _reservedBlock;
+        private readonly List<MemoryBlock> _mappedBlocks;
+        private ulong _mappedBlockUsage;
+
+        private readonly ulong[] _mappedPageBitmap;
+
+        public MemoryBlock Block => _reservedBlock;
+
+        public SparseMemoryBlock(ulong size, PageInitDelegate pageInit, MemoryBlock fill)
+        {
+            _pageSize = MemoryBlock.GetPageSize();
+            _reservedBlock = new MemoryBlock(size, MemoryAllocationFlags.Reserve | MemoryAllocationFlags.ViewCompatible);
+            _mappedBlocks = new List<MemoryBlock>();
+            _pageInit = pageInit;
+
+            int pages = (int)BitUtils.DivRoundUp(size, _pageSize);
+            int bitmapEntries = BitUtils.DivRoundUp(pages, 64);
+            _mappedPageBitmap = new ulong[bitmapEntries];
+
+            if (fill != null)
+            {
+                // Fill the block with mappings from the fill block.
+
+                if (fill.Size % _pageSize != 0)
+                {
+                    throw new ArgumentException("Fill memory block should be page aligned.", nameof(fill));
+                }
+
+                int repeats = (int)BitUtils.DivRoundUp(size, fill.Size);
+
+                ulong offset = 0;
+                for (int i = 0; i < repeats; i++)
+                {
+                    _reservedBlock.MapView(fill, 0, offset, Math.Min(fill.Size, size - offset));
+                    offset += fill.Size;
+                }
+            }
+
+            // If a fill block isn't provided, the pages that aren't EnsureMapped are unmapped.
+            // The caller can rely on signal handler to fill empty pages instead.
+        }
+
+        private void MapPage(ulong pageOffset)
+        {
+            // Take a page from the latest mapped block.
+            MemoryBlock block = _mappedBlocks.LastOrDefault();
+
+            if (block == null || _mappedBlockUsage == MapGranularity)
+            {
+                // Need to map some more memory.
+
+                block = new MemoryBlock(MapGranularity, MemoryAllocationFlags.Mirrorable | MemoryAllocationFlags.NoMap);
+
+                _mappedBlocks.Add(block);
+
+                _mappedBlockUsage = 0;
+            }
+
+            _reservedBlock.MapView(block, _mappedBlockUsage, pageOffset, _pageSize);
+            _pageInit(_reservedBlock.GetSpan(pageOffset, (int)_pageSize));
+
+            _mappedBlockUsage += _pageSize;
+        }
+
+        public void EnsureMapped(ulong offset)
+        {
+            int pageIndex = (int)(offset / _pageSize);
+            int bitmapIndex = pageIndex >> 6;
+
+            ref ulong entry = ref _mappedPageBitmap[bitmapIndex];
+            ulong bit = 1UL << (pageIndex & 63);
+
+            if ((entry & bit) == 0)
+            {
+                // Not mapped.
+
+                lock (_lock)
+                {
+                    // Check the bit while locked to make sure that this only happens once.
+
+                    if ((entry & bit) == 0)
+                    {
+                        MapPage(offset & ~(_pageSize - 1));
+
+                        entry |= bit;
+                    }
+                }
+            }
+        }
+
+        public void Dispose()
+        {
+            _reservedBlock.Dispose();
+
+            foreach (MemoryBlock block in _mappedBlocks)
+            {
+                block.Dispose();
+            }
+
+            GC.SuppressFinalize(this);
+        }
+    }
+}