linux-kernel - Re: [RFC 3/9] ext4: Add couple of more fast

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Date:   Wed, 23 Feb 2022 17:34:57 +0530
From:   Ritesh Harjani <riteshh@...ux.ibm.com>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org,
        Harshad Shirwadkar <harshadshirwadkar@...il.com>,
        "Theodore Ts'o" <tytso@....edu>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC 3/9] ext4: Add couple of more fast_commit tracepoints

On 22/02/23 12:53PM, Jan Kara wrote:
> On Wed 23-02-22 15:41:59, Ritesh Harjani wrote:
> > On 22/02/23 10:40AM, Jan Kara wrote:
> > > On Wed 23-02-22 02:04:11, Ritesh Harjani wrote:
> > > > This adds two more tracepoints for ext4_fc_track_template() &
> > > > ext4_fc_cleanup() which are helpful in debugging some fast_commit issues.
> > > >
> > > > Signed-off-by: Ritesh Harjani <riteshh@...ux.ibm.com>
> > >
> > > So why is this more useful than trace_ext4_fc_track_range() and other
> > > tracepoints? I don't think it provides any more information? What am I
> > > missing?
> >
> > Thanks Jan for all the reviews.
> >
> > So ext4_fc_track_template() adds almost all required information
> > (including the caller info) in this one trace point along with transaction tid
> > which is useful for tracking issue similar to what is mentioned in Patch-9.
> >
> > (race with if inode is part of two transactions tid where jbd2 full commit
> > may begin for txn n-1 while inode is still in sbi->s_fc_q[MAIN])
>
> I understand commit tid is interesting but cannot we just add it to
> tracepoints like trace_ext4_fc_track_range() directly? It would seem useful
> to have it there and when it is there, the need for
> ext4_fc_track_template() is not really big. I don't care too much but

Yes make sense. Sure, I will look into adding this info to existing trace
points then. With that I think trace_ext4_fc_track_template() won't be required.

Will add those changes in V2.

> this tracepoint looked a bit superfluous to me.
>
> > And similarly ext4_fc_cleanup() helps with that information about which tid
> > completed and whether it was called from jbd2 full commit or from fast_commit.
>
> Yeah, that one is clear.

Will retain trace_ext4_fc_cleanup() then.


-ritesh
>
> 								Honza
> --
> Jan Kara <jack@...e.com>
> SUSE Labs, CR