eventfs: Move tracing/events to eventfs

Up until now, /sys/kernel/tracing/events was no different than any other
part of tracefs. The files and directories within the events directory was
created when the tracefs was mounted, and also created for the instances in
/sys/kernel/tracing/instances/<instance>/events. Most of these files and
directories will never be referenced. Since there are thousands of these
files and directories they spend their time wasting precious memory
resources.

Move the "events" directory to the new eventfs. The eventfs will take the
meta data of the events that they represent and store that. When the files
in the events directory are referenced, the dentry and inodes to represent
them are then created. When the files are no longer referenced, they are
freed. This saves the precious memory resources that were wasted on these
seldom referenced dentries and inodes.

Running the following:

 ~# cat /proc/meminfo /proc/slabinfo  > before.out
 ~# mkdir /sys/kernel/tracing/instances/foo
 ~# cat /proc/meminfo /proc/slabinfo  > after.out

to test the changes produces the following deltas:

Before this change:

 Before after deltas for meminfo:

   MemFree: -32260
   MemAvailable: -21496
   KReclaimable: 21528
   Slab: 22440
   SReclaimable: 21528
   SUnreclaim: 912
   VmallocUsed: 16

 Before after deltas for slabinfo:

   <slab>:		<objects>	[ * <size> = <total>]

   tracefs_inode_cache:	14472		[* 1184 = 17134848]
   buffer_head:		24		[* 168 = 4032]
   hmem_inode_cache:	28		[* 1480 = 41440]
   dentry:		14450		[* 312 = 4508400]
   lsm_inode_cache:	14453		[* 32 = 462496]
   vma_lock:		11		[* 152 = 1672]
   vm_area_struct:	2		[* 184 = 368]
   trace_event_file:	1748		[* 88 = 153824]
   kmalloc-256:		1072		[* 256 = 274432]
   kmalloc-64:		2842		[* 64 = 181888]

 Total slab additions in size: 22,763,400 bytes

With this change:

 Before after deltas for meminfo:

   MemFree: -12600
   MemAvailable: -12580
   Cached: 24
   Active: 12
   Inactive: 68
   Inactive(anon): 48
   Active(file): 12
   Inactive(file): 20
   Dirty: -4
   AnonPages: 68
   KReclaimable: 12
   Slab: 1856
   SReclaimable: 12
   SUnreclaim: 1844
   KernelStack: 16
   PageTables: 36
   VmallocUsed: 16

 Before after deltas for slabinfo:

   <slab>:		<objects>	[ * <size> = <total>]

   tracefs_inode_cache:	108		[* 1184 = 127872]
   buffer_head:		24		[* 168 = 4032]
   hmem_inode_cache:	18		[* 1480 = 26640]
   dentry:		127		[* 312 = 39624]
   lsm_inode_cache:	152		[* 32 = 4864]
   vma_lock:		67		[* 152 = 10184]
   vm_area_struct:	-12		[* 184 = -2208]
   trace_event_file: 	1764		[* 96 = 169344]
   kmalloc-96:		14322		[* 96 = 1374912]
   kmalloc-64:		2814		[* 64 = 180096]
   kmalloc-32:		1103		[* 32 = 35296]
   kmalloc-16:		2308		[* 16 = 36928]
   kmalloc-8:		12800		[* 8 = 102400]

 Total slab additions in size: 2,109,984 bytes

Which is a savings of 20,653,416 bytes (20 MB) per tracing instance.

Link: https://lkml.kernel.org/r/1690568452-46553-10-git-send-email-akaher@vmware.comSigned-off-by: Ajay Kaher <akaher@vmware.com>
Co-developed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Tested-by: Ching-lin Yu <chinglinyu@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

fs/tracefs/inode.c

@@ -374,6 +374,23 @@ static const struct super_operations tracefs_super_operations = {
 	.show_options	= tracefs_show_options,
 };
 
+static void tracefs_dentry_iput(struct dentry *dentry, struct inode *inode)
+{
+	struct tracefs_inode *ti;
+
+	if (!dentry || !inode)
+		return;
+
+	ti = get_tracefs(inode);
+	if (ti && ti->flags & TRACEFS_EVENT_INODE)
+		eventfs_set_ef_status_free(dentry);
+	iput(inode);
+}
+
+static const struct dentry_operations tracefs_dentry_operations = {
+	.d_iput = tracefs_dentry_iput,
+};
+
 static int trace_fill_super(struct super_block *sb, void *data, int silent)
 {
 	static const struct tree_descr trace_files[] = {{""}};
@@ -396,6 +413,7 @@ static int trace_fill_super(struct super_block *sb, void *data, int silent)
 		goto fail;
 
 	sb->s_op = &tracefs_super_operations;
+	sb->s_d_op = &tracefs_dentry_operations;
 
 	tracefs_apply_options(sb, false);
 

include/linux/trace_events.h

@@ -638,6 +638,7 @@ struct trace_event_file {
 	struct list_head		list;
 	struct trace_event_call		*event_call;
 	struct event_filter __rcu	*filter;
+	struct eventfs_file             *ef;
 	struct dentry			*dir;
 	struct trace_array		*tr;
 	struct trace_subsystem_dir	*system;

kernel/trace/trace.h

@@ -1334,7 +1334,7 @@ struct trace_subsystem_dir {
 	struct list_head		list;
 	struct event_subsystem		*subsystem;
 	struct trace_array		*tr;
-	struct dentry			*entry;
+	struct eventfs_file             *ef;
 	int				ref_count;
 	int				nr_events;
 };

kernel/trace/trace_events.c

@@ -984,7 +984,7 @@ static void remove_subsystem(struct trace_subsystem_dir *dir)
 		return;
 
 	if (!--dir->nr_events) {
-		tracefs_remove(dir->entry);
+		eventfs_remove(dir->ef);
 		list_del(&dir->list);
 		__put_system_dir(dir);
 	}
@@ -1005,7 +1005,7 @@ static void remove_event_file_dir(struct trace_event_file *file)
 
 		tracefs_remove(dir);
 	}
-
+	eventfs_remove(file->ef);
 	list_del(&file->list);
 	remove_subsystem(file->system);
 	free_event_filter(file->filter);
@@ -2291,13 +2291,13 @@ create_new_subsystem(const char *name)
 	return NULL;
 }
 
-static struct dentry *
+static struct eventfs_file *
 event_subsystem_dir(struct trace_array *tr, const char *name,
 		    struct trace_event_file *file, struct dentry *parent)
 {
 	struct event_subsystem *system, *iter;
 	struct trace_subsystem_dir *dir;
-	struct dentry *entry;
+	int res;
 
 	/* First see if we did not already create this dir */
 	list_for_each_entry(dir, &tr->systems, list) {
@@ -2305,7 +2305,7 @@ event_subsystem_dir(struct trace_array *tr, const char *name,
 		if (strcmp(system->name, name) == 0) {
 			dir->nr_events++;
 			file->system = dir;
-			return dir->entry;
+			return dir->ef;
 		}
 	}
 
@@ -2329,8 +2329,8 @@ event_subsystem_dir(struct trace_array *tr, const char *name,
 	} else
 		__get_system(system);
 
-	dir->entry = tracefs_create_dir(name, parent);
-	if (!dir->entry) {
+	dir->ef = eventfs_add_subsystem_dir(name, parent);
+	if (IS_ERR(dir->ef)) {
 		pr_warn("Failed to create system directory %s\n", name);
 		__put_system(system);
 		goto out_free;
@@ -2345,22 +2345,22 @@ event_subsystem_dir(struct trace_array *tr, const char *name,
 	/* the ftrace system is special, do not create enable or filter files */
 	if (strcmp(name, "ftrace") != 0) {
 
-		entry = tracefs_create_file("filter", TRACE_MODE_WRITE,
-					    dir->entry, dir,
+		res = eventfs_add_file("filter", TRACE_MODE_WRITE,
+					    dir->ef, dir,
 					    &ftrace_subsystem_filter_fops);
-		if (!entry) {
+		if (res) {
 			kfree(system->filter);
 			system->filter = NULL;
 			pr_warn("Could not create tracefs '%s/filter' entry\n", name);
 		}
 
-		trace_create_file("enable", TRACE_MODE_WRITE, dir->entry, dir,
+		eventfs_add_file("enable", TRACE_MODE_WRITE, dir->ef, dir,
 				  &ftrace_system_enable_fops);
 	}
 
 	list_add(&dir->list, &tr->systems);
 
-	return dir->entry;
+	return dir->ef;
 
  out_free:
 	kfree(dir);
@@ -2413,8 +2413,8 @@ static int
 event_create_dir(struct dentry *parent, struct trace_event_file *file)
 {
 	struct trace_event_call *call = file->event_call;
+	struct eventfs_file *ef_subsystem = NULL;
 	struct trace_array *tr = file->tr;
-	struct dentry *d_events;
 	const char *name;
 	int ret;
 
@@ -2426,24 +2426,24 @@ event_create_dir(struct dentry *parent, struct trace_event_file *file)
 	if (WARN_ON_ONCE(strcmp(call->class->system, TRACE_SYSTEM) == 0))
 		return -ENODEV;
 
-	d_events = event_subsystem_dir(tr, call->class->system, file, parent);
-	if (!d_events)
+	ef_subsystem = event_subsystem_dir(tr, call->class->system, file, parent);
+	if (!ef_subsystem)
 		return -ENOMEM;
 
 	name = trace_event_name(call);
-	file->dir = tracefs_create_dir(name, d_events);
-	if (!file->dir) {
+	file->ef = eventfs_add_dir(name, ef_subsystem);
+	if (IS_ERR(file->ef)) {
 		pr_warn("Could not create tracefs '%s' directory\n", name);
 		return -1;
 	}
 
 	if (call->class->reg && !(call->flags & TRACE_EVENT_FL_IGNORE_ENABLE))
-		trace_create_file("enable", TRACE_MODE_WRITE, file->dir, file,
+		eventfs_add_file("enable", TRACE_MODE_WRITE, file->ef, file,
 				  &ftrace_enable_fops);
 
 #ifdef CONFIG_PERF_EVENTS
 	if (call->event.type && call->class->reg)
-		trace_create_file("id", TRACE_MODE_READ, file->dir,
+		eventfs_add_file("id", TRACE_MODE_READ, file->ef,
 				  (void *)(long)call->event.type,
 				  &ftrace_event_id_fops);
 #endif
@@ -2459,27 +2459,27 @@ event_create_dir(struct dentry *parent, struct trace_event_file *file)
 	 * triggers or filters.
 	 */
 	if (!(call->flags & TRACE_EVENT_FL_IGNORE_ENABLE)) {
-		trace_create_file("filter", TRACE_MODE_WRITE, file->dir,
+		eventfs_add_file("filter", TRACE_MODE_WRITE, file->ef,
 				  file, &ftrace_event_filter_fops);
 
-		trace_create_file("trigger", TRACE_MODE_WRITE, file->dir,
+		eventfs_add_file("trigger", TRACE_MODE_WRITE, file->ef,
 				  file, &event_trigger_fops);
 	}
 
 #ifdef CONFIG_HIST_TRIGGERS
-	trace_create_file("hist", TRACE_MODE_READ, file->dir, file,
+	eventfs_add_file("hist", TRACE_MODE_READ, file->ef, file,
 			  &event_hist_fops);
 #endif
 #ifdef CONFIG_HIST_TRIGGERS_DEBUG
-	trace_create_file("hist_debug", TRACE_MODE_READ, file->dir, file,
+	eventfs_add_file("hist_debug", TRACE_MODE_READ, file->ef, file,
 			  &event_hist_debug_fops);
 #endif
-	trace_create_file("format", TRACE_MODE_READ, file->dir, call,
+	eventfs_add_file("format", TRACE_MODE_READ, file->ef, call,
 			  &ftrace_event_format_fops);
 
 #ifdef CONFIG_TRACE_EVENT_INJECT
 	if (call->event.type && call->class->reg)
-		trace_create_file("inject", 0200, file->dir, file,
+		eventfs_add_file("inject", 0200, file->ef, file,
 				  &event_inject_fops);
 #endif
 
@@ -3632,21 +3632,22 @@ create_event_toplevel_files(struct dentry *parent, struct trace_array *tr)
 {
 	struct dentry *d_events;
 	struct dentry *entry;
+	int error = 0;
 
 	entry = trace_create_file("set_event", TRACE_MODE_WRITE, parent,
 				  tr, &ftrace_set_event_fops);
 	if (!entry)
 		return -ENOMEM;
 
-	d_events = tracefs_create_dir("events", parent);
-	if (!d_events) {
+	d_events = eventfs_create_events_dir("events", parent);
+	if (IS_ERR(d_events)) {
 		pr_warn("Could not create tracefs 'events' directory\n");
 		return -ENOMEM;
 	}
 
-	entry = trace_create_file("enable", TRACE_MODE_WRITE, d_events,
+	error = eventfs_add_events_file("enable", TRACE_MODE_WRITE, d_events,
 				  tr, &ftrace_tr_enable_fops);
-	if (!entry)
+	if (error)
 		return -ENOMEM;
 
 	/* There are not as crucial, just warn if they are not created */
@@ -3659,11 +3660,11 @@ create_event_toplevel_files(struct dentry *parent, struct trace_array *tr)
 			  &ftrace_set_event_notrace_pid_fops);
 
 	/* ring buffer internal formats */
-	trace_create_file("header_page", TRACE_MODE_READ, d_events,
+	eventfs_add_events_file("header_page", TRACE_MODE_READ, d_events,
 				  ring_buffer_print_page_header,
 				  &ftrace_show_header_fops);
 
-	trace_create_file("header_event", TRACE_MODE_READ, d_events,
+	eventfs_add_events_file("header_event", TRACE_MODE_READ, d_events,
 				  ring_buffer_print_entry_header,
 				  &ftrace_show_header_fops);
 
@@ -3751,7 +3752,7 @@ int event_trace_del_tracer(struct trace_array *tr)
 
 	down_write(&trace_event_sem);
 	__trace_remove_event_dirs(tr);
-	tracefs_remove(tr->event_dir);
+	eventfs_remove_events_dir(tr->event_dir);
 	up_write(&trace_event_sem);
 
 	tr->event_dir = NULL;