linux-kernel - Re: [PATCH v2] ext4: fix fast commit inode enqueueing during a full journal commit

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Message-ID: <87h6eirl49.fsf@brahms.olymp>
Date: Tue, 28 May 2024 16:50:46 +0100
From: Luis Henriques <luis.henriques@...ux.dev>
To: Jan Kara <jack@...e.cz>
Cc: Theodore Ts'o <tytso@....edu>,  Andreas Dilger <adilger@...ger.ca>,
  Harshad Shirwadkar <harshadshirwadkar@...il.com>,
  linux-ext4@...r.kernel.org,  linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] ext4: fix fast commit inode enqueueing during a full
 journal commit

On Tue 28 May 2024 12:52:03 PM +02, Jan Kara wrote;

> On Tue 28-05-24 12:36:02, Jan Kara wrote:
>> On Mon 27-05-24 16:48:24, Luis Henriques wrote:
>> > On Mon 27 May 2024 09:29:40 AM +01, Luis Henriques wrote;
>> > >>> +	/*
>> > >>> +	 * Used to flag an inode as part of the next fast commit; will be
>> > >>> +	 * reset during fast commit clean-up
>> > >>> +	 */
>> > >>> +	tid_t i_fc_next;
>> > >>> +
>> > >>
>> > >> Do we really need new tid in the inode? I'd be kind of hoping we could use
>> > >> EXT4_I(inode)->i_sync_tid for this - I can see we even already set it in
>> > >> ext4_fc_track_template() and used for similar comparisons in fast commit
>> > >> code.
>> > >
>> > > Ah, true.  It looks like it could be used indeed.  We'll still need a flag
>> > > here, but a simple bool should be enough for that.
>> > 
>> > After looking again at the code, I'm not 100% sure that this is actually
>> > doable.  For example, if I replace the above by
>> > 
>> > 	bool i_fc_next;
>> > 
>> > and set to to 'true' below:
>
> Forgot to comment on this one: I don't think you even need 'bool i_fc_next'
> - simply whenever i_sync_tid is greater than committing transaction's tid,
> you move the inode to FC_Q_STAGING list in ext4_fc_cleanup().

Yeah, I got that from your other comment in the previous email.  And that
means the actual fix will be a pretty small patch (almost a one-liner).

I'm running some more tests on v3, I'll probably send it later today or
tomorrow.  Thanks a lot for your review (and patience), Jan.

Cheers,
-- 
Luís