First implementation of slab allocator. Needs more testing and polishing

1 files changed, 217 insertions, 0 deletions

diff --git a/kernel/lib/slab_alloc.c b/kernel/lib/slab_alloc.c
new file mode 100644
index 0000000..e1aa8b5
--- /dev/null
+++ b/kernel/lib/slab_alloc.c
@@ -0,0 +1,217 @@
+#include <slab_alloc.h>
+
+typedef struct object {
+	struct object *next;
+} object_t;
+
+typedef struct cache {
+	struct {	// pack this so that it takes less space...
+		uint32_t is_a_cache		: 1;		// if not, this is a region allocated alone
+		uint32_t n_free_objs	: 31;
+	};
+
+	union {
+		struct {	// when this is a cache
+			object_t* first_free_obj;
+			struct cache *next_cache;
+		} c;
+		struct {	// when this is a region allocated alone
+			size_t region_size;
+		} sr;
+	};
+
+	size_t region_addr;
+	struct cache *next_region;
+} cache_t;
+
+typedef struct slab {
+	cache_t *first_cache;		// linked list of caches
+} slab_t;
+
+struct mem_allocator {
+	const slab_type_t *types;
+	slab_t *slabs;
+	cache_t *first_free_region_descriptor;
+	cache_t *all_regions;
+
+	page_alloc_fun_t alloc_fun;
+	page_free_fun_t free_fun;
+};
+
+// ============================================== //
+// Helper functions for the manipulation of lists //
+// ============================================== //
+
+void add_free_region_descriptor(mem_allocator_t *a, cache_t *c) {
+	c->next_region = a->first_free_region_descriptor;
+	a->first_free_region_descriptor = c;
+}
+
+cache_t *take_region_descriptor(mem_allocator_t *a) {
+	if (a->first_free_region_descriptor == 0) {
+		// TODO : allocate more descriptors	(not complicated)
+		return 0;
+	}
+	cache_t *x = a->first_free_region_descriptor;
+	a->first_free_region_descriptor = x->next_region;
+	return x;
+}
+
+// ============================== //
+// The actual allocator functions //
+// ============================== //
+
+mem_allocator_t* create_slab_allocator(const slab_type_t *types, page_alloc_fun_t af, page_free_fun_t ff) {
+	union {
+		size_t addr;
+		mem_allocator_t *a;
+		slab_t *s;
+		cache_t *c;
+	} ptr;
+
+	ptr.addr = (size_t)af(PAGE_SIZE);
+	if (ptr.addr == 0) return 0;	// could not allocate
+	size_t end_addr = ptr.addr + PAGE_SIZE;
+
+	mem_allocator_t *a = ptr.a;
+	ptr.a++;
+
+	a->all_regions = 0;
+	a->alloc_fun = af;
+	a->free_fun = ff;
+
+	a->types = types;
+	a->slabs = ptr.s;
+	for (const slab_type_t *t = types; t->obj_size != 0; t++) {
+		ptr.s->first_cache = 0;
+		ptr.s++;
+	}
+
+	a->first_free_region_descriptor = 0;
+	while ((size_t)(ptr.c + 1) <= end_addr) {
+		add_free_region_descriptor(a, ptr.c);
+		ptr.c++;
+	}
+
+	return a;
+}
+
+static void stack_and_destroy_regions(page_free_fun_t ff, cache_t *r) {
+	if (r == 0) return;
+	size_t addr = r->region_addr;
+	stack_and_destroy_regions(ff, r->next_region);
+	ff((void*)addr);
+}
+void destroy_slab_allocator(mem_allocator_t *a) {
+	stack_and_destroy_regions(a->free_fun, a->all_regions);
+	a->free_fun(a);
+}
+
+void* slab_alloc(mem_allocator_t* a, const size_t sz) {
+	for (int i = 0; a->types[i].obj_size != 0; i++) {
+		const size_t obj_size = a->types[i].obj_size;
+		if (sz <= obj_size) {
+			// find a cache with free space
+			cache_t *fc = a->slabs[i].first_cache;
+			while (fc != 0 && fc->n_free_objs == 0) {
+				ASSERT(fc->c.first_free_obj == 0); // make sure n_free == 0 iff no object in the free stack
+				fc = fc->c.next_cache;
+			}
+			// if none found, try to allocate a new one
+			if (fc == 0) {
+				fc = take_region_descriptor(a);
+				if (fc == 0) return 0;
+
+				const size_t cache_size = a->types[i].pages_per_cache * PAGE_SIZE;
+				fc->region_addr = (size_t)a->alloc_fun(cache_size);
+				if (fc->region_addr == 0) {
+					add_free_region_descriptor(a, fc);
+					return 0;
+				}
+
+				fc->is_a_cache = 1;
+				fc->n_free_objs = 0;
+				fc->c.first_free_obj = 0;
+				for (size_t i = fc->region_addr; i + obj_size <= fc->region_addr + cache_size; i += obj_size) {
+					object_t *x = (object_t*)i;
+					x->next = fc->c.first_free_obj;
+					fc->c.first_free_obj = x;
+					fc->n_free_objs++;
+				}
+				ASSERT(fc->n_free_objs == cache_size / obj_size);
+
+				fc->next_region = a->all_regions;
+				a->all_regions = fc;
+				fc->c.next_cache = a->slabs[i].first_cache;
+				a->slabs[i].first_cache = fc;
+			}
+			// allocate on fc
+			ASSERT(fc != 0 && fc->n_free_objs > 0);
+			object_t *x = fc->c.first_free_obj;
+			fc->c.first_free_obj = x->next;
+			fc->n_free_objs--;
+			// TODO : if fc is full, put it at the end
+			return (void*)x;
+		}
+	}
+
+	// otherwise directly allocate using a->alloc_fun
+	cache_t *r = take_region_descriptor(a);
+	if (r == 0) return 0;
+
+	r->region_addr = (size_t)a->alloc_fun(sz);
+	if (r->region_addr == 0) {
+		add_free_region_descriptor(a, r);
+		return 0;
+	} else {
+		r->is_a_cache =  0;
+		r->sr.region_size = sz;
+
+		r->next_region = a->all_regions;
+		a->all_regions = r;
+
+		return (void*)r->region_addr;
+	}
+}
+
+void slab_free(mem_allocator_t* a, const void* ptr) {
+	const size_t addr = (size_t)ptr;
+
+	for (int i = 0; a->types[i].obj_size != 0; i++) {
+		size_t region_size = PAGE_SIZE * a->types[i].pages_per_cache;
+		for (cache_t *r = a->slabs[i].first_cache; r != 0; r = r->c.next_cache) {
+			if (addr >= r->region_addr && addr < r->region_addr + region_size) {
+				ASSERT((addr - r->region_addr) % a->types[i].obj_size == 0);
+				ASSERT(r->is_a_cache);
+				object_t *o = (object_t*)addr;
+				o->next = r->c.first_free_obj;
+				r->c.first_free_obj = o;
+				r->n_free_objs++;
+				// TODO : if cache is empty, free it
+				return;
+			}
+		}
+	}
+
+	// otherwise the block was directly allocated : look for it in regions.
+	a->free_fun(ptr);
+	ASSERT(a->all_regions != 0);
+
+	if (a->all_regions->region_addr == addr) {
+		cache_t *r = a->all_regions;
+		ASSERT(r->is_a_cache == 0);
+		a->all_regions = r->next_region;
+		add_free_region_descriptor(a, r);
+	} else {
+		for (cache_t *i = a->all_regions; i->next_region != 0; i = i->next_region) {
+			if (i->next_region->region_addr == addr) {
+				cache_t *r = i->next_region;
+				ASSERT(r->is_a_cache == 0);
+				i->next_region = r->next_region;
+				add_free_region_descriptor(a, r);
+				return;
+			}
+		}
+		ASSERT(false);
+	}
+}