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

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