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.com

Signed-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>

1 files changed, 18 insertions, 0 deletions

diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
index d9273066f25f..bb6de89eb446 100644
--- a/fs/tracefs/inode.c
+++ b/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);