linux-ext4 - [RFC 0/9] ext4: Improve FC trace events and discuss one FC failure

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Date:   Wed, 23 Feb 2022 02:04:08 +0530
From:   Ritesh Harjani <riteshh@...ux.ibm.com>
To:     linux-ext4@...r.kernel.org
Cc:     Harshad Shirwadkar <harshadshirwadkar@...il.com>,
        "Theodore Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ritesh Harjani <riteshh@...ux.ibm.com>
Subject: [RFC 0/9] ext4: Improve FC trace events and discuss one FC failure

Hello,

Sending this RFC out for getting some review comments/suggestions on the
problem listed in this cover letter. It would be helpful if someone has any
pointers around these.

1. Patch-2 fixes the problem reported by Steven about dereferencing pointers from
   the ring buffer [1].
	One of the problem in this patch which I might need some help is, how to
	expose EXT4_FC_REASON_MAX enum for
	+	__array(unsigned int, fc_ineligible_rc, EXT4_FC_REASON_MAX)

	My observation is that this trace_event is correctly printing the array
	values when called from cat /sys/kernel/debug/tracing/trace_pipe.

	But when I am using perf record -e ext4:ext4_fc_stats to record these trace
	events, I am seeing the array values to be all 0.

	Do you know what will be the right and easy way to fix above, so that this works
	properly for perf tools too? And we should be able to backport this too.

2. Patch-9 discusses one of the problem where FC might miss to track/commit
   inode's update. This also needs some discussion. I have added my observations
   on the commit log of patch-9 itself.

3. Remaining are FC trace event improvement patches, which I found useful while
   debugging some of the recent fast_commit issues.

Also a careful review of patches is always helpful :)


[1]: https://lore.kernel.org/linux-ext4/20220221160916.333e6491@rorschach.local.home/T/#u

Ritesh Harjani (9):
  ext4: Remove unused enum EXT4_FC_COMMIT_FAILED
  ext4: Fix ext4_fc_stats trace point
  ext4: Add couple of more fast_commit tracepoints
  ext4: Do not call FC trace event if FS does not support FC
  ext4: Add commit_tid info in jbd debug log
  ext4: Add commit tid info in ext4_fc_commit_start/stop trace events
  ext4: Fix remaining two trace events to use same printk convention
  ext4: Convert ext4_fc_track_dentry type events to use event class
  ext4: fast_commit missing tracking updates to a file

 fs/ext4/fast_commit.c       |  30 +++--
 fs/ext4/fast_commit.h       |   1 -
 include/trace/events/ext4.h | 229 +++++++++++++++++++++++++-----------
 3 files changed, 182 insertions(+), 78 deletions(-)

--
2.31.1