cache: Shared meter for memory usage

src/cache.c

@@ -18,7 +18,9 @@
 GIT__USE_OIDMAP
 
 bool git_cache__enabled = true;
-size_t git_cache__max_storage = (4 * 1024 * 1024);
+int64_t git_cache__max_storage = (4 * 1024 * 1024);
+
+static git_atomic64 git_cache__current_storage = {0};
 
 static size_t git_cache__max_object_size[8] = {
 	0,     /* GIT_OBJ__EXT1 */
@@ -81,6 +83,7 @@ static void clear_cache(git_cache *cache)
 	});
 
 	kh_clear(oid, cache->map);
+	git_atomic64_add(&git_cache__current_storage, -cache->used_memory);
 	cache->used_memory = 0;
 }
 
@@ -106,7 +109,7 @@ void git_cache_free(git_cache *cache)
 static void cache_evict_entries(git_cache *cache)
 {
 	uint32_t seed = rand();
-	size_t evict_count = 8;
+	int64_t evicted_memory = 0, evict_count = 8;
 
 	/* do not infinite loop if there's not enough entries to evict  */
 	if (evict_count > kh_size(cache->map)) {
@@ -121,12 +124,15 @@ static void cache_evict_entries(git_cache *cache)
 			git_cached_obj *evict = kh_val(cache->map, pos);
 
 			evict_count--;
-			cache->used_memory -= evict->size;
+			evicted_memory += evict->size;
 			git_cached_obj_decref(evict);
 
 			kh_del(oid, cache->map, pos);
 		}
 	}
+
+	cache->used_memory -= evicted_memory;
+	git_atomic64_add(&git_cache__current_storage, -evicted_memory);
 }
 
 static bool cache_should_store(git_otype object_type, size_t object_size)
@@ -171,7 +177,8 @@ static void *cache_store(git_cache *cache, git_cached_obj *entry)
 	if (git_mutex_lock(&cache->lock) < 0)
 		return entry;
 
-	if (cache->used_memory > git_cache__max_storage)
+	/* soften the load on the cache */
+	if (git_cache__current_storage.val > git_cache__max_storage)
 		cache_evict_entries(cache);
 
 	pos = kh_get(oid, cache->map, &entry->oid);
@@ -186,6 +193,7 @@ static void *cache_store(git_cache *cache, git_cached_obj *entry)
 			kh_val(cache->map, pos) = entry;
 			git_cached_obj_incref(entry);
 			cache->used_memory += entry->size;
+			git_atomic64_add(&git_cache__current_storage, (int64_t)entry->size);
 		}
 	}
 	/* found */

src/cache.h

@@ -31,11 +31,11 @@ typedef struct {
 typedef struct {
 	git_oidmap *map;
 	git_mutex   lock;
-	size_t      used_memory;
+	int64_t     used_memory;
 } git_cache;
 
 extern bool git_cache__enabled;
-extern size_t git_cache__max_storage;
+extern int64_t git_cache__max_storage;
 
 int git_cache_set_max_object_size(git_otype type, size_t size);
 

src/util.c

@@ -39,7 +39,6 @@ int git_libgit2_capabilities()
 /* Declarations for tuneable settings */
 extern size_t git_mwindow__window_size;
 extern size_t git_mwindow__mapped_limit;
-extern size_t git_odb__cache_size;
 
 static int config_level_to_futils_dir(int config_level)
 {
@@ -104,7 +103,7 @@ int git_libgit2_opts(int key, ...)
 		}
 
 	case GIT_OPT_SET_CACHE_MAX_SIZE:
-		git_cache__max_storage = va_arg(ap, size_t);
+		git_cache__max_storage = va_arg(ap, int64_t);
 		break;
 
 	case GIT_OPT_ENABLE_CACHING: