Re: [PATCH v2 0/3] btrfs: trace: Add trace events for extent_io_tree

[David Sterba <dsterba@suse.cz>]

On Fri, Mar 01, 2019 at 10:47:57AM +0800, Qu Wenruo wrote:
> - Allow NULL fs_info for TP_fast_assign_fsid()
>   There is extent bits operation in selftest which is too deep to pass
>   fs_info. And since it's in selftest, it shouldn't trigger trace
>   events.
>   But to be safe, we still need to check fs_indo in
>   TP_fast_assign_fsid(), for NULL fs_info, just keep fsid filled with
>   zero.

Ok, better be safe here. I'd still like to remove the conditional, as
the tests typically access only a single filesystem we could export the
fs_info globally, avoiding the need to pass it around.

> There is one point which need extra attention:
> 1) Those trace events are pretty heavy
>    The following workload would generate over 400 trace events.

I'm not sure if 400 is considered a lot, I'd say 400.000 would be a lot
for the steps below.

> 	mkfs.btrfs -f $dev
> 	start_trace
> 	mount $dev $mnt -o enospc_debug
> 	sync
> 	touch $mnt/file1
> 	touch $mnt/file2
> 	touch $mnt/file3
> 	xfs_io -f -c "pwrite 0 16k" $mnt/file4
> 	umount $mnt
> 	end_trace
>    It's not recommended to use them in real world environment.
> 
> Changelog:
> v2:
> - Introduce fs_info to distinguish different btrfs filesystems
> - Code style change to make trace code more elegant
> - Minor IO_TREE_* naming change.
> - Use btrfs_ino() to replace raw inode number.
> - Change extent_io_tree::owner declaration to avoid affecting spinlock.

v2 looks good to me, thanks. I'll add it to the 5.2 queue.