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//! Kernel Heap Allocator
const heap_const = @import("../common/constants/heap.zig");
const memory_const = @import("../common/constants/memory.zig");
const pmm = @import("pmm.zig");
const serial = @import("../drivers/serial/serial.zig");
const PAGE_SIZE = memory_const.PAGE_SIZE;
const HIGHER_HALF = memory_const.HIGHER_HALF_START;
const SlabHeader = struct {
free_count: usize,
total_count: usize,
object_size: usize,
next_slab: ?*SlabHeader,
prev_slab: ?*SlabHeader,
first_free: ?*FreeObject,
};
const FreeObject = struct {
next: ?*FreeObject,
};
const SlabCache = struct {
object_size: usize,
objects_per_slab: usize,
slab_list: ?*SlabHeader,
};
var caches: [heap_const.NUM_CACHES]SlabCache = undefined;
var initialized: bool = false;
pub fn init() void {
serial.print("\n=== Heap ===\n");
for (0..heap_const.NUM_CACHES) |i| {
const size = heap_const.SIZE_CLASSES[i];
const usable_space = PAGE_SIZE - @sizeOf(SlabHeader);
const objects_per_slab = usable_space / size;
caches[i] = SlabCache{
.object_size = size,
.objects_per_slab = objects_per_slab,
.slab_list = null,
};
serial.printf("Cache {}B: {} objects/slab\n", .{ size, objects_per_slab });
}
initialized = true;
serial.print("Heap ready\n");
}
pub fn alloc(size: usize) ?[*]u8 {
if (!initialized) return null;
if (size == 0) return null;
if (size > heap_const.LARGE_ALLOC_THRESHOLD) {
return alloc_large(size);
}
const cache_idx = find_cache_index(size);
return alloc_from_cache(&caches[cache_idx]);
}
pub fn free(ptr: [*]u8, size: usize) void {
if (!initialized) return;
if (size == 0) return;
if (size > heap_const.LARGE_ALLOC_THRESHOLD) {
free_large(ptr, size);
return;
}
const cache_idx = find_cache_index(size);
free_to_cache(&caches[cache_idx], ptr);
}
fn find_cache_index(size: usize) usize {
for (0..heap_const.NUM_CACHES) |i| {
if (size <= heap_const.SIZE_CLASSES[i]) {
return i;
}
}
return heap_const.NUM_CACHES - 1;
}
fn alloc_from_cache(cache: *SlabCache) ?[*]u8 {
var current_slab = cache.slab_list;
while (current_slab) |slab| {
if (slab.free_count > 0) {
return alloc_from_slab(slab);
}
current_slab = slab.next_slab;
}
const new_slab = create_slab(cache) orelse return null;
new_slab.next_slab = cache.slab_list;
new_slab.prev_slab = null;
if (cache.slab_list) |first| {
first.prev_slab = new_slab;
}
cache.slab_list = new_slab;
return alloc_from_slab(new_slab);
}
fn create_slab(cache: *SlabCache) ?*SlabHeader {
const phys_page = pmm.alloc_page() orelse return null;
const virt_addr = phys_page + HIGHER_HALF;
const page_ptr: [*]volatile u8 = @ptrFromInt(virt_addr);
for (0..PAGE_SIZE) |i| {
page_ptr[i] = 0;
}
const slab: *SlabHeader = @ptrFromInt(virt_addr);
slab.free_count = cache.objects_per_slab;
slab.total_count = cache.objects_per_slab;
slab.object_size = cache.object_size;
slab.next_slab = null;
slab.prev_slab = null;
const first_obj_addr = virt_addr + @sizeOf(SlabHeader);
for (0..cache.objects_per_slab) |j| {
const obj_addr = first_obj_addr + (j * cache.object_size);
const obj: *FreeObject = @ptrFromInt(obj_addr);
if (j + 1 < cache.objects_per_slab) {
const next_addr = obj_addr + cache.object_size;
obj.next = @ptrFromInt(next_addr);
} else {
obj.next = null;
}
}
slab.first_free = @ptrFromInt(first_obj_addr);
return slab;
}
fn alloc_from_slab(slab: *SlabHeader) ?[*]u8 {
if (slab.first_free) |free_obj| {
slab.first_free = free_obj.next;
slab.free_count -= 1;
return @ptrFromInt(@intFromPtr(free_obj));
}
return null;
}
fn free_to_cache(cache: *SlabCache, ptr: [*]u8) void {
const ptr_addr = @intFromPtr(ptr);
const slab_addr = ptr_addr & ~@as(u64, PAGE_SIZE - 1);
const slab: *SlabHeader = @ptrFromInt(slab_addr);
const obj: *FreeObject = @ptrFromInt(ptr_addr);
obj.next = slab.first_free;
slab.first_free = obj;
slab.free_count += 1;
if (slab.free_count == slab.total_count) {
if (slab.next_slab != null or slab.prev_slab != null) {
return_slab_to_pmm(cache, slab);
}
}
}
fn return_slab_to_pmm(cache: *SlabCache, slab: *SlabHeader) void {
if (slab.prev_slab) |prev| {
prev.next_slab = slab.next_slab;
} else {
cache.slab_list = slab.next_slab;
}
if (slab.next_slab) |next| {
next.prev_slab = slab.prev_slab;
}
const slab_addr = @intFromPtr(slab);
const phys_addr = slab_addr - HIGHER_HALF;
pmm.free_page(phys_addr);
}
fn alloc_large(size: usize) ?[*]u8 {
const num_pages = (size + PAGE_SIZE - 1) / PAGE_SIZE;
var pages: [heap_const.MAX_LARGE_PAGES]u64 = undefined;
if (num_pages > heap_const.MAX_LARGE_PAGES) return null;
for (0..num_pages) |i| {
pages[i] = pmm.alloc_page() orelse {
for (0..i) |j| {
pmm.free_page(pages[j]);
}
return null;
};
}
const result: [*]u8 = @ptrFromInt(pages[0] + HIGHER_HALF);
return result;
}
fn free_large(ptr: [*]u8, size: usize) void {
const num_pages = (size + PAGE_SIZE - 1) / PAGE_SIZE;
const base_virt = @intFromPtr(ptr);
const base_phys = base_virt - HIGHER_HALF;
for (0..num_pages) |i| {
pmm.free_page(base_phys + (i * PAGE_SIZE));
}
}
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