1 files changed, 283 insertions, 0 deletions
diff --git a/src/common/libkogata/slab_alloc.c b/src/common/libkogata/slab_alloc.c
new file mode 100644
index 0000000..714c49f
--- /dev/null
+++ b/src/common/libkogata/slab_alloc.c
@@ -0,0 +1,283 @@
+#include <slab_alloc.h>
+
+typedef struct object {
+	struct object *next;
+} object_t;
+
+typedef struct cache {
+	void* region_addr;
+	
+	uint32_t n_free_objs;
+	object_t* first_free_obj;
+
+	struct cache *next_cache;	// next cache in this slab
+} cache_t;
+
+typedef struct region {
+	void* region_addr;
+	size_t region_size;
+	struct region *next_region;
+	bool contains_descriptors;
+} region_t;
+
+typedef union descriptor {
+	cache_t c;
+	region_t r;
+	union descriptor *next_free;
+} descriptor_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;
+
+	descriptor_t *first_free_descriptor;
+	region_t *all_regions;
+
+	page_alloc_fun_t alloc_fun;
+	page_free_fun_t free_fun;
+};
+
+// ============================================== //
+// Helper functions for the manipulation of lists //
+// ============================================== //
+
+static void add_free_descriptor(mem_allocator_t *a, descriptor_t *c) {
+	c->next_free = a->first_free_descriptor;
+	a->first_free_descriptor = c;
+}
+
+static descriptor_t *take_descriptor(mem_allocator_t *a) {
+	if (a->first_free_descriptor == 0) {
+		void* p = a->alloc_fun(PAGE_SIZE);
+		if (p == 0) return 0;
+
+		const void* end = p + PAGE_SIZE;
+		for (descriptor_t *i = (descriptor_t*)p; i + 1 <= (descriptor_t*)end; i++) {
+			add_free_descriptor(a, i);
+		}
+
+		// register the descriptor region
+		descriptor_t *dd = a->first_free_descriptor;
+		ASSERT(dd != 0);
+		a->first_free_descriptor = dd->next_free;
+
+		region_t *drd = &dd->r;
+		drd->region_addr = p;
+		drd->region_size = PAGE_SIZE;
+		drd->contains_descriptors = true;
+		drd->next_region = a->all_regions;
+		a->all_regions = drd;
+	}
+
+	descriptor_t *x = a->first_free_descriptor;
+	ASSERT(x != 0);
+	a->first_free_descriptor = x->next_free;
+	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 {
+		void* addr;
+		mem_allocator_t *a;
+		slab_t *s;
+		descriptor_t *d;
+	} ptr;
+
+	ptr.addr = af(PAGE_SIZE);
+	if (ptr.addr == 0) return 0;	// could not allocate
+	const void* 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++) {
+		ASSERT(t->obj_size >= sizeof(object_t));
+		ptr.s->first_cache = 0;
+		ptr.s++;
+	}
+
+	a->first_free_descriptor = 0;
+	while (ptr.d + 1 <= (descriptor_t*)end_addr) {
+		add_free_descriptor(a, ptr.d);
+		ptr.d++;
+	}
+
+	return a;
+}
+
+static void stack_and_destroy_regions(page_free_fun_t ff, region_t *r) {
+	if (r == 0) return;
+	void* addr = r->region_addr;
+	ASSERT(r != r->next_region);
+	stack_and_destroy_regions(ff, r->next_region);
+	ff(addr);
+}
+void destroy_slab_allocator(mem_allocator_t *a) {
+	for (int i = 0; a->types[i].obj_size != 0; i++) {
+		for (cache_t *c = a->slabs[i].first_cache; c != 0; c = c->next_cache) {
+			a->free_fun(c->region_addr);
+		}
+	}
+	region_t *dr = 0;
+	region_t *i = a->all_regions;
+	while (i != 0) {
+		region_t *r = i;
+		i = r->next_region;
+		if (r->contains_descriptors) {
+			r->next_region = dr;
+			dr = r;
+		} else {
+			a->free_fun(r->region_addr);
+		}
+	}
+	stack_and_destroy_regions(a->free_fun, dr);
+	a->free_fun(a);
+}
+
+void* slab_alloc(mem_allocator_t* a, 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->first_free_obj == 0); // make sure n_free == 0 iff no object in the free stack
+				fc = fc->next_cache;
+			}
+			// if none found, try to allocate a new one
+			if (fc == 0) {
+				descriptor_t *fcd = take_descriptor(a);
+				if (fcd == 0) return 0;
+
+				fc = &fcd->c;
+				ASSERT((descriptor_t*)fc == fcd);
+
+				const size_t cache_size = a->types[i].pages_per_cache * PAGE_SIZE;
+				fc->region_addr = a->alloc_fun(cache_size);
+				if (fc->region_addr == 0) {
+					add_free_descriptor(a, fcd);
+					return 0;
+				}
+
+				fc->n_free_objs = 0;
+				fc->first_free_obj = 0;
+				for (void* p = fc->region_addr; p + obj_size <= fc->region_addr + cache_size; p += obj_size) {
+					object_t *x = (object_t*)p;
+					x->next = fc->first_free_obj;
+					fc->first_free_obj = x;
+					fc->n_free_objs++;
+				}
+				ASSERT(fc->n_free_objs == cache_size / obj_size);
+
+				fc->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->first_free_obj;
+			fc->first_free_obj = x->next;
+			fc->n_free_objs--;
+
+			ASSERT((fc->n_free_objs == 0) == (fc->first_free_obj == 0));
+
+			// TODO : if fc is full, put it at the end
+			return x;
+		}
+	}
+
+	// otherwise directly allocate using a->alloc_fun
+	descriptor_t *rd = take_descriptor(a);
+	if (rd == 0) return 0;
+	region_t *r = &rd->r;
+	ASSERT((descriptor_t*)r == rd);
+
+	r->region_addr = a->alloc_fun(sz);
+	if (r->region_addr == 0) {
+		add_free_descriptor(a, rd);
+		return 0;
+	} else {
+		r->region_size = sz;
+		r->contains_descriptors = false;
+
+		r->next_region = a->all_regions;
+		a->all_regions = r;
+
+		return (void*)r->region_addr;
+	}
+}
+
+void slab_free(mem_allocator_t* a, void* addr) {
+
+	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->next_cache) {
+			if (addr >= r->region_addr && addr < r->region_addr + region_size) {
+				ASSERT((addr - r->region_addr) % a->types[i].obj_size == 0);
+
+				object_t *o = (object_t*)addr;
+				o->next = r->first_free_obj;
+				r->first_free_obj = o;
+				r->n_free_objs++;
+
+				if (r->n_free_objs == region_size / a->types[i].obj_size) {
+					// region is completely unused, free it.
+					if (a->slabs[i].first_cache == r) {
+						a->slabs[i].first_cache = r->next_cache;
+					} else {
+						for (cache_t *it = a->slabs[i].first_cache; it->next_cache != 0; it = it->next_cache) {
+							if (it->next_cache == r) {
+								it->next_cache = r->next_cache;
+								break;
+							}
+						}
+					}
+					a->free_fun(r->region_addr);
+					add_free_descriptor(a, (descriptor_t*)r);
+				}
+				return;
+			}
+		}
+	}
+
+	// otherwise the block was directly allocated : look for it in regions.
+	ASSERT(a->all_regions != 0);
+
+	if (a->all_regions->region_addr == addr) {
+		a->free_fun(addr);	// found it, free it
+
+		region_t *r = a->all_regions;
+		a->all_regions = r->next_region;
+		add_free_descriptor(a, (descriptor_t*)r);
+	} else {
+		for (region_t *i = a->all_regions; i->next_region != 0; i = i->next_region) {
+			if (i->next_region->region_addr == addr) {
+				a->free_fun(addr);	// found it, free it
+
+				region_t *r = i->next_region;
+				ASSERT(!r->contains_descriptors);
+				i->next_region = r->next_region;
+				add_free_descriptor(a, (descriptor_t*)r);
+				return;
+			}
+		}
+		ASSERT(false);
+	}
+}
+
+/* vim: set ts=4 sw=4 tw=0 noet :*/
+