KPath: Use an object_cache for the path buffers in the normal case.

This was (following the packagefs changes) the number-one (by call
count) consumer of malloc() during the boot -- 52866 calls, and 100%
of them either 1024 or 1025 bytes!

Virtually all of these are ephemeral (indeed, the object_cache
stats after a boot with this patch shows there is only a single slab
of 64 buffers allocated, and most of them unused), so this is
probably a significant performance boost.

Change-Id: I659f5707510cbfeafa735d35eea7b92732ead666

headers/private/kernel/fs/KPath.h

@@ -23,14 +23,14 @@ class KPath {
 		LAZY_ALLOC = 0x04
 	};
 public:
-								KPath(size_t bufferSize = B_PATH_NAME_LENGTH);
+								KPath(size_t bufferSize = B_PATH_NAME_LENGTH + 1);
 								KPath(const char* path, int32 flags = DEFAULT,
-									size_t bufferSize = B_PATH_NAME_LENGTH);
+									size_t bufferSize = B_PATH_NAME_LENGTH + 1);
 								KPath(const KPath& other);
 								~KPath();
 
 			status_t			SetTo(const char* path, int32 flags = DEFAULT,
-									size_t bufferSize = B_PATH_NAME_LENGTH);
+									size_t bufferSize = B_PATH_NAME_LENGTH + 1);
 			void				Adopt(KPath& other);
 
 			status_t			InitCheck() const;
@@ -67,6 +67,7 @@ class KPath {
 
 private:
 			status_t			_AllocateBuffer();
+			void				_FreeBuffer();
 			status_t			_Normalize(const char* path,
 									bool traverseLeafLink);
 			void				_ChopTrailingSlashes();

src/system/kernel/disk_device_manager/KDiskDeviceManager.cpp

@@ -197,7 +197,7 @@ class KDiskDeviceManager::DeviceWatcher : public NotificationListener {
 
 		if (strcmp(event->name, "raw") == 0) {
 			// a new raw device was added/removed
-			KPath path(B_PATH_NAME_LENGTH + 1);
+			KPath path;
 			if (path.InitCheck() != B_OK
 				|| vfs_entry_ref_to_path(event->device, event->directory,
 					event->name, true, path.LockBuffer(),

src/system/kernel/fs/KPath.cpp

@@ -15,13 +15,19 @@
 
 #include <team.h>
 #include <vfs.h>
+#include <slab/Slab.h>
 
 
 // debugging
 #define TRACE(x) ;
 //#define TRACE(x) dprintf x
 
 
+#ifdef _KERNEL_MODE
+extern object_cache* sPathNameCache;
+#endif
+
+
 KPath::KPath(size_t bufferSize)
 	:
 	fBuffer(NULL),
@@ -66,20 +72,19 @@ KPath::KPath(const KPath& other)
 
 KPath::~KPath()
 {
-	free(fBuffer);
+	_FreeBuffer();
 }
 
 
 status_t
 KPath::SetTo(const char* path, int32 flags, size_t bufferSize)
 {
 	if (bufferSize == 0)
-		bufferSize = B_PATH_NAME_LENGTH;
+		bufferSize = B_PATH_NAME_LENGTH + 1;
 
 	// free the previous buffer, if the buffer size differs
 	if (fBuffer != NULL && fBufferSize != bufferSize) {
-		free(fBuffer);
-		fBuffer = NULL;
+		_FreeBuffer();
 		fBufferSize = 0;
 	}
 
@@ -102,7 +107,7 @@ KPath::SetTo(const char* path, int32 flags, size_t bufferSize)
 void
 KPath::Adopt(KPath& other)
 {
-	free(fBuffer);
+	_FreeBuffer();
 
 	fBuffer = other.fBuffer;
 	fBufferSize = other.fBufferSize;
@@ -218,7 +223,9 @@ void
 KPath::UnlockBuffer()
 {
 	if (!fLocked) {
-		TRACE(("KPath::UnlockBuffer(): ERROR: Buffer not locked!\n"));
+#ifdef _KERNEL_MODE
+		panic("KPath::UnlockBuffer(): Buffer not locked!");
+#endif
 		return;
 	}
 
@@ -242,6 +249,12 @@ KPath::DetachBuffer()
 {
 	char* buffer = fBuffer;
 
+	if (fBufferSize == (B_PATH_NAME_LENGTH + 1)) {
+		buffer = (char*)malloc(fBufferSize);
+		memcpy(buffer, fBuffer, fBufferSize);
+		_FreeBuffer();
+	}
+
 	if (fBuffer != NULL) {
 		fBuffer = NULL;
 		fPathLength = 0;
@@ -412,8 +425,14 @@ KPath::operator!=(const char* path) const
 status_t
 KPath::_AllocateBuffer()
 {
-	if (fBuffer == NULL && fBufferSize != 0)
-		fBuffer = (char*)malloc(fBufferSize);
+	if (fBuffer == NULL && fBufferSize != 0) {
+#ifdef _KERNEL_MODE
+		if (fBufferSize == (B_PATH_NAME_LENGTH + 1))
+			fBuffer = (char*)object_cache_alloc(sPathNameCache, 0);
+		else
+#endif
+			fBuffer = (char*)malloc(fBufferSize);
+	}
 	if (fBuffer == NULL) {
 		fFailed = true;
 		return B_NO_MEMORY;
@@ -425,6 +444,19 @@ KPath::_AllocateBuffer()
 }
 
 
+void
+KPath::_FreeBuffer()
+{
+#ifdef _KERNEL_MODE
+	if (fBufferSize == (B_PATH_NAME_LENGTH + 1))
+		object_cache_free(sPathNameCache, fBuffer, 0);
+	else
+#endif
+		free(fBuffer);
+	fBuffer = NULL;
+}
+
+
 status_t
 KPath::_Normalize(const char* path, bool traverseLeafLink)
 {