commit b9ba8cf2eb8519ede72176d1541599d194f1dfd1
author Kalesh Singh <kaleshsingh@google.com> Tue Jul 27 15:17:29 2021 +0000
committer Kalesh Singh <kaleshsingh@google.com> Wed Jul 28 13:45:15 2021 +0000
tree c3210c5dcaad605fc2cecd58900eaca379e3a45d
parent 2c7d7d9680fcd7d12c7a6bea4537c858bfd2ea1a

mm_events: Add knob to remove mm_event tracing instance

Only create mm_event tracing instance if
persist.mm_events.enabled=true. This saves ~5.5MB on low
memory devices that don't enable mm_events. The memory saved is
slab memory that would be allocated for the ftrace instance's
inode/dentry objects.

Set the per-CPU trace buffer sizes to 1KB by default to minimize
trace buffer memory usage if perfetto isn't started.

Also disable tracing by default, traced_probes will enable
as needed.

Bug: 194156702
Test: boot; ls /sys/kernel/tracing/instances -> No mm_events
Test: setprop persist.mm_events.enabled true; boot;
      ls /sys/kernel/tracing/instances -> mm_events
Change-Id: I89d7e5e1cd0d32b5612bc419b1a1c4b8c3c8ade6

cmds/atrace/atrace.rc

diff --git a/cmds/atrace/atrace.rc b/cmds/atrace/atrace.rc
index 37fc9a9..e3c4ede 100644
--- a/cmds/atrace/atrace.rc
+++ b/cmds/atrace/atrace.rc
@@ -266,7 +266,10 @@
     chmod 0666 /sys/kernel/debug/tracing/per_cpu/cpu15/trace
     chmod 0666 /sys/kernel/tracing/per_cpu/cpu15/trace
 
-on post-fs-data
+# Only create the tracing instance if persist.mm_events.enabled
+# Attempting to remove the tracing instance after it has been created
+# will likely fail with EBUSY as it would be in use by traced_probes.
+on post-fs-data && property:persist.mm_events.enabled=true
 # Create MM Events Tracing Instance for Kmem Activity Trigger
     mkdir /sys/kernel/debug/tracing/instances/mm_events 0755 system system
     mkdir /sys/kernel/tracing/instances/mm_events 0755 system system
@@ -275,10 +278,18 @@
     chmod 0666 /sys/kernel/debug/tracing/instances/mm_events/buffer_size_kb
     chmod 0666 /sys/kernel/tracing/instances/mm_events/buffer_size_kb
 
+# Set the default buffer size to the minimum
+    write /sys/kernel/debug/tracing/instances/mm_events/buffer_size_kb 1
+    write /sys/kernel/tracing/instances/mm_events/buffer_size_kb 1
+
 # Read and enable tracing
     chmod 0666 /sys/kernel/debug/tracing/instances/mm_events/tracing_on
     chmod 0666 /sys/kernel/tracing/instances/mm_events/tracing_on
 
+# Tracing disabled by default
+    write /sys/kernel/debug/tracing/instances/mm_events/tracing_on 0
+    write /sys/kernel/tracing/instances/mm_events/tracing_on 0
+
 # Read and truncate kernel trace
     chmod 0666 /sys/kernel/debug/tracing/instances/mm_events/trace
     chmod 0666 /sys/kernel/tracing/instances/mm_events/trace