ocfs2: track local alloc state via debugfs

A per-mount debugfs file, "local_alloc" is created which when read will
expose live state of the nodes local alloc file. Performance impact is
minimal, only a bit of memory overhead per mount point. Still, the code is
hidden behind CONFIG_OCFS2_FS_STATS. This feature will help us debug
local alloc performance problems on a live system.
Signed-off-by: Mark Fasheh <mfasheh@suse.com>

fs/ocfs2/localalloc.c

@@ -28,6 +28,7 @@
 #include <linux/slab.h>
 #include <linux/highmem.h>
 #include <linux/bitops.h>
+#include <linux/debugfs.h>
 
 #define MLOG_MASK_PREFIX ML_DISK_ALLOC
 #include <cluster/masklog.h>
@@ -73,6 +74,85 @@ static int ocfs2_local_alloc_new_window(struct ocfs2_super *osb,
 static int ocfs2_local_alloc_slide_window(struct ocfs2_super *osb,
 					  struct inode *local_alloc_inode);
 
+#ifdef CONFIG_OCFS2_FS_STATS
+
+DEFINE_MUTEX(la_debug_mutex);
+
+static int ocfs2_la_debug_open(struct inode *inode, struct file *file)
+{
+	file->private_data = inode->i_private;
+	return 0;
+}
+
+#define LA_DEBUG_BUF_SZ	PAGE_CACHE_SIZE
+#define LA_DEBUG_VER	1
+static ssize_t ocfs2_la_debug_read(struct file *file, char __user *userbuf,
+				   size_t count, loff_t *ppos)
+{
+	struct ocfs2_super *osb = file->private_data;
+	int written, ret;
+	char *buf = osb->local_alloc_debug_buf;
+
+	mutex_lock(&la_debug_mutex);
+	memset(buf, 0, LA_DEBUG_BUF_SZ);
+
+	written = snprintf(buf, LA_DEBUG_BUF_SZ,
+			   "0x%x\t0x%llx\t%u\t%u\t0x%x\n",
+			   LA_DEBUG_VER,
+			   (unsigned long long)osb->la_last_gd,
+			   osb->local_alloc_default_bits,
+			   osb->local_alloc_bits, osb->local_alloc_state);
+
+	ret = simple_read_from_buffer(userbuf, count, ppos, buf, written);
+
+	mutex_unlock(&la_debug_mutex);
+	return ret;
+}
+
+static const struct file_operations ocfs2_la_debug_fops = {
+	.open =		ocfs2_la_debug_open,
+	.read =		ocfs2_la_debug_read,
+};
+
+static void ocfs2_init_la_debug(struct ocfs2_super *osb)
+{
+	osb->local_alloc_debug_buf = kmalloc(LA_DEBUG_BUF_SZ, GFP_NOFS);
+	if (!osb->local_alloc_debug_buf)
+		return;
+
+	osb->local_alloc_debug = debugfs_create_file("local_alloc_stats",
+						     S_IFREG|S_IRUSR,
+						     osb->osb_debug_root,
+						     osb,
+						     &ocfs2_la_debug_fops);
+	if (!osb->local_alloc_debug) {
+		kfree(osb->local_alloc_debug_buf);
+		osb->local_alloc_debug_buf = NULL;
+	}
+}
+
+static void ocfs2_shutdown_la_debug(struct ocfs2_super *osb)
+{
+	if (osb->local_alloc_debug)
+		debugfs_remove(osb->local_alloc_debug);
+
+	if (osb->local_alloc_debug_buf)
+		kfree(osb->local_alloc_debug_buf);
+
+	osb->local_alloc_debug_buf = NULL;
+	osb->local_alloc_debug = NULL;
+}
+#else	/* CONFIG_OCFS2_FS_STATS */
+static void ocfs2_init_la_debug(struct ocfs2_super *osb)
+{
+	return;
+}
+static void ocfs2_shutdown_la_debug(struct ocfs2_super *osb)
+{
+	return;
+}
+#endif
+
 static inline int ocfs2_la_state_enabled(struct ocfs2_super *osb)
 {
 	return (osb->local_alloc_state == OCFS2_LA_THROTTLED ||
@@ -146,6 +226,8 @@ int ocfs2_load_local_alloc(struct ocfs2_super *osb)
 
 	mlog_entry_void();
 
+	ocfs2_init_la_debug(osb);
+
 	if (osb->local_alloc_bits == 0)
 		goto bail;
 
@@ -218,6 +300,9 @@ bail:
 	if (inode)
 		iput(inode);
 
+	if (status < 0)
+		ocfs2_shutdown_la_debug(osb);
+
 	mlog(0, "Local alloc window bits = %d\n", osb->local_alloc_bits);
 
 	mlog_exit(status);
@@ -247,6 +332,8 @@ void ocfs2_shutdown_local_alloc(struct ocfs2_super *osb)
 	cancel_delayed_work(&osb->la_enable_wq);
 	flush_workqueue(ocfs2_wq);
 
+	ocfs2_shutdown_la_debug(osb);
+
 	if (osb->local_alloc_state == OCFS2_LA_UNUSED)
 		goto out;
 

fs/ocfs2/ocfs2.h

@@ -272,6 +272,11 @@ struct ocfs2_super
 
 	u64 la_last_gd;
 
+#ifdef CONFIG_OCFS2_FS_STATS
+	struct dentry *local_alloc_debug;
+	char *local_alloc_debug_buf;
+#endif
+
 	/* Next two fields are for local node slot recovery during
 	 * mount. */
 	int dirty;