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system: Split heap blocks more or less equally if possible

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This commit is contained in:
Gabriel 2025-03-07 20:08:56 +01:00
parent f41ad7e747
commit e699eb4cfa
1 changed files with 46 additions and 27 deletions

73
system/lib/heap.zig

@ -78,10 +78,10 @@ const MEMORY_BLOCK_FREE_TAG = 0xffeeffcc;
const MEMORY_BLOCK_USED_TAG = 0xee55ee66;
const MemoryBlockStatus = enum(u16) {
BlockDefault = 0,
BlockUsed = 1 << 0,
BlockStartOfMemory = 1 << 1,
BlockEndOfMemory = 1 << 2,
Default = 0,
Used = 1 << 0,
StartOfMemoryRange = 1 << 1,
EndOfMemoryRange = 1 << 2,
};
const MemoryBlockTag = packed struct {
@ -124,7 +124,7 @@ pub const SystemAllocator = struct {
}
fn isBlockFree(block: *MemoryBlockList.Node) bool {
return (block.data.status & @intFromEnum(MemoryBlockStatus.BlockUsed)) == 0;
return (block.data.status & @intFromEnum(MemoryBlockStatus.Used)) == 0;
}
fn checkStatus(block: *MemoryBlockList.Node, status: MemoryBlockStatus) bool {
@ -150,17 +150,36 @@ pub const SystemAllocator = struct {
return object_address - @sizeOf(MemoryBlockList.Node);
}
fn alignOffset(block: *MemoryBlockList.Node, offset: usize, alignment: usize) usize {
var block_address = @intFromPtr(ptrFromBlockNode(block)) + offset;
block_address = alignBlockAddressDownwards(block_address, alignment);
return block_address - @intFromPtr(ptrFromBlockNode(block));
}
fn getFairSplitOffset(block: *MemoryBlockList.Node, min: usize, alignment: usize) ?u64 {
var available = spaceAvailable(block);
available -= min; // reserve at least min size for the new block.
available -= @divTrunc(available, 2); // reserve half of the rest for the new block, while still leaving another half for the old one.
available -= @rem(available, 16); // Everything has to be aligned on a 16-byte boundary
const block_offset = alignOffset(block, available + block.data.used, alignment);
if (block_offset < block.data.used) return null;
return block_offset;
}
fn getSplitOffset(block: *MemoryBlockList.Node, min: usize, alignment: usize) ?u64 {
if (getFairSplitOffset(block, min, alignment)) |offset| return offset;
// Otherwise, allocate space at the end of the block.
var available = spaceAvailable(block);
available -= min; // reserve only min size for the new block.
var block_offset = available + block.data.used;
var block_address = @intFromPtr(ptrFromBlockNode(block)) + block_offset;
block_address = alignBlockAddressDownwards(block_address, alignment);
block_offset = block_address - @intFromPtr(ptrFromBlockNode(block));
const block_offset = alignOffset(block, available + block.data.used, alignment);
if (block_offset < block.data.used) return null;
return block_offset;
@ -180,10 +199,10 @@ pub const SystemAllocator = struct {
new_node.data.tag = MEMORY_BLOCK_USED_TAG;
if (checkStatus(block, MemoryBlockStatus.BlockEndOfMemory)) {
new_node.data.status = @intFromEnum(MemoryBlockStatus.BlockEndOfMemory);
if (checkStatus(block, MemoryBlockStatus.EndOfMemoryRange)) {
new_node.data.status = @intFromEnum(MemoryBlockStatus.EndOfMemoryRange);
} else {
new_node.data.status = @intFromEnum(MemoryBlockStatus.BlockDefault);
new_node.data.status = @intFromEnum(MemoryBlockStatus.Default);
}
new_node.data.allocated = old_size - (offset + @sizeOf(MemoryBlockList.Node));
@ -192,46 +211,46 @@ pub const SystemAllocator = struct {
list.insertAfter(block, new_node);
block.data.status &= ~@intFromEnum(MemoryBlockStatus.BlockEndOfMemory); // this block is no longer the last block in its memory range
block.data.status &= ~@intFromEnum(MemoryBlockStatus.EndOfMemoryRange); // this block is no longer the last block in its memory range
return new_node;
}
fn combineForward(list: *MemoryBlockList, block: *MemoryBlockList.Node) void {
// This block ends a memory range, cannot be combined with blocks outside its range.
if (checkStatus(block, MemoryBlockStatus.BlockEndOfMemory)) return;
if (checkStatus(block, MemoryBlockStatus.EndOfMemoryRange)) return;
// The caller needs to ensure there is a next block.
const next = block.next.?;
// This block starts a memory range, cannot be combined with blocks outside its range.
if (checkStatus(next, MemoryBlockStatus.BlockStartOfMemory)) return;
if (checkStatus(next, MemoryBlockStatus.StartOfMemoryRange)) return;
list.remove(next);
next.data.tag = MEMORY_BLOCK_FREE_TAG;
block.data.allocated += next.data.allocated + @sizeOf(MemoryBlockList.Node);
if (checkStatus(next, MemoryBlockStatus.BlockEndOfMemory)) {
block.data.status |= @intFromEnum(MemoryBlockStatus.BlockEndOfMemory);
if (checkStatus(next, MemoryBlockStatus.EndOfMemoryRange)) {
block.data.status |= @intFromEnum(MemoryBlockStatus.EndOfMemoryRange);
}
}
fn combineBackward(list: *MemoryBlockList, block: *MemoryBlockList.Node) *MemoryBlockList.Node {
// This block starts a memory range, cannot be combined with blocks outside its range.
if (checkStatus(block, MemoryBlockStatus.BlockStartOfMemory)) return block;
if (checkStatus(block, MemoryBlockStatus.StartOfMemoryRange)) return block;
// The caller needs to ensure there is a last block.
const last = block.prev.?;
// This block ends a memory range, cannot be combined with blocks outside its range.
if (checkStatus(last, MemoryBlockStatus.BlockEndOfMemory)) return block;
if (checkStatus(last, MemoryBlockStatus.EndOfMemoryRange)) return block;
list.remove(block);
block.data.tag = MEMORY_BLOCK_FREE_TAG;
last.data.allocated += block.data.allocated + @sizeOf(MemoryBlockList.Node);
if (checkStatus(block, MemoryBlockStatus.BlockEndOfMemory)) {
last.data.status |= @intFromEnum(MemoryBlockStatus.BlockEndOfMemory);
if (checkStatus(block, MemoryBlockStatus.EndOfMemoryRange)) {
last.data.status |= @intFromEnum(MemoryBlockStatus.EndOfMemoryRange);
}
return last;
@ -273,7 +292,7 @@ pub const SystemAllocator = struct {
node.data.allocated = (pages * PAGE_SIZE) - (@sizeOf(MemoryBlockList.Node) + padding);
node.data.tag = MEMORY_BLOCK_USED_TAG;
node.data.status = @intFromEnum(MemoryBlockStatus.BlockStartOfMemory) | @intFromEnum(MemoryBlockStatus.BlockEndOfMemory);
node.data.status = @intFromEnum(MemoryBlockStatus.StartOfMemoryRange) | @intFromEnum(MemoryBlockStatus.EndOfMemoryRange);
node.data.alignment = @truncate(alignment);
node.data.base_address = base_address;
self.tags.append(node);
@ -284,7 +303,7 @@ pub const SystemAllocator = struct {
const tag = iter.?;
tag.data.used = len;
tag.data.status |= @intFromEnum(MemoryBlockStatus.BlockUsed);
tag.data.status |= @intFromEnum(MemoryBlockStatus.Used);
return ptrFromBlockNode(tag);
}
@ -317,7 +336,7 @@ pub const SystemAllocator = struct {
if (block.data.alignment != alignment) return;
if (!isBlockFree(block)) return;
block.data.status &= ~@intFromEnum(MemoryBlockStatus.BlockUsed);
block.data.status &= ~@intFromEnum(MemoryBlockStatus.Used);
const maybe_next = block.next;
if (maybe_next) |next| {
@ -329,7 +348,7 @@ pub const SystemAllocator = struct {
if (isBlockFree(last)) block = combineBackward(&self.tags, block);
}
if (checkStatus(block, MemoryBlockStatus.BlockStartOfMemory) and checkStatus(block, MemoryBlockStatus.BlockEndOfMemory)) {
if (checkStatus(block, MemoryBlockStatus.StartOfMemoryRange) and checkStatus(block, MemoryBlockStatus.EndOfMemoryRange)) {
self.tags.remove(block);
const base_address = block.data.base_address;