Re: [PATCH v4 00/10] tracing: introducing eventfs

Steven Rostedt
2023-07-14T22:58:31Z

On Thu, 13 Jul 2023 17:03:14 +0530
Ajay Kaher <akaher@vmware.com> wrote:

> Events Tracing infrastructure contains lot of files, directories
> (internally in terms of inodes, dentries). And ends up by consuming
> memory in MBs. We can have multiple events of Events Tracing, which
> further requires more memory.
>
> Instead of creating inodes/dentries, eventfs could keep meta-data and
> skip the creation of inodes/dentries. As and when require, eventfs will
> create the inodes/dentries only for required files/directories.
> Also eventfs would delete the inodes/dentries once no more requires
> but preserve the meta data.
>
> Tracing events took ~9MB, with this approach it took ~4.5MB
> for ~10K files/dir.

I think we are very close to getting this in for the next merge window. I
ran several tests and so far it's holding up!

I made a bunch of nits for this series, but nothing major. Mostly fixing up
change logs and comments, as well as some naming conventions and
reorganizing the series a little bit.

Anyway, I'm hoping that v5 will be ready to go into linux-next.

Thanks a lot Ajay for working on this!

-- Steve

>
> v3:
> Patch 3,4,5,7,9:
> removed all the eventfs_rwsem code and replaced it with an srcu
> lock for the readers, and a mutex to synchronize the writers of
> the list.
>
> Patch 2: moved 'tracefs_inode' and 'get_tracefs()' to v4 03/10
>
> Patch 3: moved the struct eventfs_file and eventfs_inode into event_inode.c
> as it really should not be exposed to all users.
>
> Patch 5: added a recursion check to eventfs_remove_rec() as it is really
> dangerous to have unchecked recursion in the kernel (we do have
> a fixed size stack).
>
> have the free use srcu callbacks. After the srcu grace periods
> are done, it adds the eventfs_file onto a llist (lockless link
> list) and wakes up a work queue. Then the work queue does the
> freeing (this needs to be done in task/workqueue context, as
> srcu callbacks are done in softirq context).
>
> Patch 6: renamed:
> eventfs_create_file() -> create_file()
> eventfs_create_dir() -> create_dir()
>
> v2:
> Patch 01: new patch:'Require all trace events to have a TRACE_SYSTEM'
> Patch 02: moved from v1 1/9
> Patch 03: moved from v1 2/9
> As suggested by Zheng Yejian, introduced eventfs_prepare_ef()
> helper function to add files or directories to eventfs
> fix WARNING reported by kernel test robot in v1 8/9
> Patch 04: moved from v1 3/9
> used eventfs_prepare_ef() to add files
> fix WARNING reported by kernel test robot in v1 8/9
> Patch 05: moved from v1 4/9
> fix compiling warning reported by kernel test robot in v1 4/9
> Patch 06: moved from v1 5/9
> Patch 07: moved from v1 6/9
> Patch 08: moved from v1 7/9
> Patch 09: moved from v1 8/9
> rebased because of v3 01/10
> Patch 10: moved from v1 9/9
>
> v1:
> Patch 1: add header file
> Patch 2: resolved kernel test robot issues
> protecting eventfs lists using nested eventfs_rwsem
> Patch 3: protecting eventfs lists using nested eventfs_rwsem
> Patch 4: improve events cleanup code to fix crashes
> Patch 5: resolved kernel test robot issues
> removed d_instantiate_anon() calls
> Patch 6: resolved kernel test robot issues
> fix kprobe test in eventfs_root_lookup()
> protecting eventfs lists using nested eventfs_rwsem
> Patch 7: remove header file
> Patch 8: pass eventfs_rwsem as argument to eventfs functions
> called eventfs_remove_events_dir() instead of tracefs_remove()
> from event_trace_del_tracer()
> Patch 9: new patch to fix kprobe test case
>
> Ajay Kaher (9):
> tracefs: Rename some tracefs function
> eventfs: Implement eventfs dir creation functions
> eventfs: Implement eventfs file add functions
> eventfs: Implement eventfs file, directory remove function
> eventfs: Implement functions to create eventfs files and directories
> eventfs: Implement eventfs lookup, read, open functions
> eventfs: Implement tracefs_inode_cache
> eventfs: Move tracing/events to eventfs
> test: ftrace: Fix kprobe test for eventfs
>
> Steven Rostedt (Google) (1):
> tracing: Require all trace events to have a TRACE_SYSTEM
>
> fs/tracefs/Makefile | 1 +
> fs/tracefs/event_inode.c | 711 ++++++++++++++++++
> fs/tracefs/inode.c | 124 ++-
> fs/tracefs/internal.h | 25 +
> include/linux/trace_events.h | 1 +
> include/linux/tracefs.h | 32 +
> kernel/trace/trace.h | 2 +-
> kernel/trace/trace_events.c | 78 +-
> .../ftrace/test.d/kprobe/kprobe_args_char.tc | 4 +-
> .../test.d/kprobe/kprobe_args_string.tc | 4 +-
> 10 files changed, 930 insertions(+), 52 deletions(-)
> create mode 100644 fs/tracefs/event_inode.c
> create mode 100644 fs/tracefs/internal.h
>