added locking to slab's Cache<>. Now we react to system's low memory conditions freeing up empty slabs.

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@20836 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/slab/Base.h

@@ -11,7 +11,12 @@
 
 #include <stdint.h>
 
+#include <KernelExport.h>
 #include <OS.h>
+
+#include <lock.h>
+#include <vm_low_memory.h>
+#include <util/AutoLock.h>
 #include <util/list.h>
 
 #ifdef __cplusplus
@@ -32,14 +37,15 @@ typedef void (*base_cache_destructor)(void *cookie, void *object);
 
 /* base Slab implementation, opaque to the backend used.
  *
- * NOTE: the caller is responsible for the Cache's locking. */
+ * NOTE: the caller is responsible for the Cache's locking.
+ *       Cache<> below handles it as well. */
 
 typedef struct base_cache {
 	char name[32];
 	size_t object_size;
 	size_t cache_color_cycle;
 	struct list empty, partial, full;
-	size_t empty_count;
+	size_t empty_count, pressure;
 	base_cache_constructor constructor;
 	base_cache_destructor destructor;
 	void *cookie;
@@ -56,11 +62,16 @@ typedef struct cache_slab {
 	struct list_link link;
 } cache_slab;
 
+// TODO add reclaim method to base_cache to be called under severe memory
+//		pressure so the slab owner can free as much buffers as possible.
+
 void base_cache_init(base_cache *cache, const char *name, size_t object_size,
 	size_t alignment, base_cache_constructor constructor,
 	base_cache_destructor destructor, void *cookie);
 void base_cache_destroy(base_cache *cache,
 	void (*return_slab)(base_cache *, cache_slab *));
+void base_cache_low_memory(base_cache *cache, int32 level,
+	void (*return_slab)(base_cache *, cache_slab *));
 
 cache_object_link *base_cache_allocate_object(base_cache *cache);
 cache_object_link *base_cache_allocate_object_with_new_slab(base_cache *cache,
@@ -83,6 +94,7 @@ typedef std::pair<cache_slab *, cache_object_link *> CacheObjectInfo;
 template<typename Strategy>
 class Cache : protected base_cache {
 public:
+	typedef Cache<Strategy>			ThisCache;
 	typedef base_cache_constructor	Constructor;
 	typedef base_cache_destructor	Destructor;
 
@@ -90,17 +102,29 @@ public:
 		Constructor constructor, Destructor destructor, void *cookie)
 		: fStrategy(this)
 	{
-		base_cache_init(this, name, objectSize, alignment, constructor,
-			destructor, cookie);
+		if (benaphore_init(&fLock, name) >= B_OK) {
+			base_cache_init(this, name, objectSize, alignment, constructor,
+				destructor, cookie);
+			register_low_memory_handler(_LowMemory, this, 0);
+		}
 	}
 
 	~Cache()
 	{
-		base_cache_destroy(this, _ReturnSlab);
+		if (fLock.sem >= B_OK) {
+			benaphore_lock(&fLock);
+			unregister_low_memory_handler(_LowMemory, this);
+			base_cache_destroy(this, _ReturnSlab);
+			benaphore_destroy(&fLock);
+		}
 	}
 
+	status_t InitCheck() const { return fLock.sem; }
+
 	void *AllocateObject(uint32_t flags)
 	{
+		BenaphoreLocker _(fLock);
+
 		cache_object_link *link = base_cache_allocate_object(this);
 
 		// if the cache is returning NULL it is because it ran out of slabs
@@ -118,6 +142,8 @@ public:
 
 	void ReturnObject(void *object)
 	{
+		BenaphoreLocker _(fLock);
+
 		CacheObjectInfo location = fStrategy.ObjectInformation(object);
 
 		if (base_cache_return_object(this, location.first, location.second))
@@ -127,9 +153,22 @@ public:
 private:
 	static void _ReturnSlab(base_cache *self, cache_slab *slab)
 	{
-		((Cache<Strategy> *)self)->fStrategy.ReturnSlab(slab);
+		// Already locked, ~Cache() -> base_cache_destroy -> _ReturnSlab
+		((ThisCache *)self)->fStrategy.ReturnSlab(slab);
 	}
 
+	static void _LowMemory(void *_self, int32 level)
+	{
+		if (level == B_NO_LOW_MEMORY)
+			return;
+
+		ThisCache *self = (ThisCache *)_self;
+
+		BenaphoreLocker _(self->fLock);
+		base_cache_low_memory(self, level, _ReturnSlab);
+	}
+
+	benaphore fLock;
 	Strategy fStrategy;
 };
 

headers/private/kernel/slab/MergedStrategy.h

@@ -9,7 +9,6 @@
 #ifndef _SLAB_MERGED_STRATEGY_H_
 #define _SLAB_MERGED_STRATEGY_H_
 
-#include <slab/Base.h>
 #include <slab/Strategy.h>
 
 

src/add-ons/kernel/network/stack/net_buffer.cpp

@@ -73,7 +73,6 @@ typedef Cache<AreaHashCacheStrategy> DataNodeCache;
 
 static NetBufferCache *sNetBufferCache;
 static DataNodeCache *sDataNodeCache;
-static benaphore sCachesLock;
 
 
 static status_t append_data(net_buffer *buffer, const void *data, size_t size);
@@ -103,7 +102,6 @@ dump_buffer(net_buffer *_buffer)
 static inline data_header *
 allocate_data_header()
 {
-	BenaphoreLocker _(sCachesLock);
 	return (data_header *)sDataNodeCache->AllocateObject(CACHE_DONT_SLEEP);
 }
 
@@ -111,7 +109,6 @@ allocate_data_header()
 static inline net_buffer_private *
 allocate_net_buffer()
 {
-	BenaphoreLocker _(sCachesLock);
 	return (net_buffer_private *)sNetBufferCache->AllocateObject(
 		CACHE_DONT_SLEEP);
 }
@@ -120,7 +117,6 @@ allocate_net_buffer()
 static inline void
 free_data_header(data_header *header)
 {
-	BenaphoreLocker _(sCachesLock);
 	sDataNodeCache->ReturnObject(header);
 }
 
@@ -128,7 +124,6 @@ free_data_header(data_header *header)
 static inline void
 free_net_buffer(net_buffer_private *buffer)
 {
-	BenaphoreLocker _(sCachesLock);
 	sNetBufferCache->ReturnObject(buffer);
 }
 
@@ -1185,25 +1180,31 @@ init_net_buffers()
 	// TODO improve our code a bit so we can add constructors
 	//		and keep around half-constructed buffers in the slab
 
-	status_t status = benaphore_init(&sCachesLock, "net buffer cache lock");
-	if (status < B_OK)
-		return status;
-
 	sNetBufferCache = new (std::nothrow) NetBufferCache("net buffer cache",
 		sizeof(net_buffer_private), 8, NULL, NULL, NULL);
-	if (sNetBufferCache == NULL) {
-		benaphore_destroy(&sCachesLock);
+	if (sNetBufferCache == NULL)
 		return B_NO_MEMORY;
+
+	status_t status = sNetBufferCache->InitCheck();
+	if (status < B_OK) {
+		delete sNetBufferCache;
+		return status;
 	}
 
 	sDataNodeCache = new (std::nothrow) DataNodeCache("data node cache",
 		BUFFER_SIZE, 0, NULL, NULL, NULL);
 	if (sDataNodeCache == NULL) {
-		benaphore_destroy(&sCachesLock);
 		delete sNetBufferCache;
 		return B_NO_MEMORY;
 	}
 
+	status = sDataNodeCache->InitCheck();
+	if (status < B_OK) {
+		delete sDataNodeCache;
+		delete sNetBufferCache;
+		return status;
+	}
+
 	return B_OK;
 }
 
@@ -1211,13 +1212,9 @@ init_net_buffers()
 status_t
 uninit_net_buffers()
 {
-	benaphore_lock(&sCachesLock);
-
 	delete sNetBufferCache;
 	delete sDataNodeCache;
 
-	benaphore_destroy(&sCachesLock);
-
 	return B_OK;
 }
 

src/system/kernel/slab/Slab.cpp

@@ -107,6 +107,9 @@ base_cache_init(base_cache *cache, const char *name, size_t objectSize,
 
 	cache->empty_count = 0;
 
+	// pressure is increased whenever we need a slab and don't have one
+	cache->pressure = 0;
+
 	cache->constructor = constructor;
 	cache->destructor = destructor;
 	cache->cookie = cookie;
@@ -132,14 +135,54 @@ base_cache_destroy(base_cache *cache,
 }
 
 
+void
+base_cache_low_memory(base_cache *cache, int32 level,
+	void (*return_slab)(base_cache *, cache_slab *))
+{
+	size_t minimumAllowed;
+
+	// only thing we can do right now is free up empty slabs
+
+	switch (level) {
+	case B_LOW_MEMORY_NOTE:
+		minimumAllowed = cache->pressure / 2 + 1;
+		break;
+
+	case B_LOW_MEMORY_WARNING:
+		cache->pressure /= 2;
+		minimumAllowed = 0;
+		break;
+
+	default:
+		cache->pressure = 0;
+		minimumAllowed = 0;
+		break;
+	}
+
+	if (cache->empty_count <= minimumAllowed)
+		return;
+
+	TRACE_CACHE(cache, "cache: memory pressure, will release down to %lu.",
+		minimumAllowed);
+
+	while (cache->empty_count > minimumAllowed) {
+		cache_slab *slab = (cache_slab *)list_remove_head_item(&cache->empty);
+		return_slab(cache, slab);
+		cache->empty_count--;
+	}
+}
+
+
 cache_object_link *
 base_cache_allocate_object(base_cache *cache)
 {
 	cache_slab *slab;
 
 	if (list_is_empty(&cache->partial)) {
-		if (list_is_empty(&cache->empty))
+		if (list_is_empty(&cache->empty)) {
+			cache->pressure++;
 			return NULL;
+		}
 
 		cache->empty_count--;
 		slab = (cache_slab *)list_remove_head_item(&cache->empty);
@@ -184,7 +227,7 @@ base_cache_return_object(base_cache *cache, cache_slab *slab,
 	if (slab->count == slab->size) {
 		list_remove_item(&cache->partial, slab);
 
-		if (cache->empty_count > 2)
+		if (cache->empty_count >= cache->pressure)
 			return 1;
 
 		cache->empty_count++;