linux-ext4 - Re: [PATCH v3 12/13] docs: Add fast commit documentation

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Message-ID: <CAD+ocbwV+f_sp9-oJyaX=9xvj_DXgLzcXu3CohVEaLDuOSx0hA@mail.gmail.com>
Date:   Wed, 30 Oct 2019 22:34:56 -0700
From:   harshad shirwadkar <harshadshirwadkar@...il.com>
To:     "Theodore Y. Ts'o" <tytso@....edu>
Cc:     Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v3 12/13] docs: Add fast commit documentation

Thanks good point. I was trying to imitate how a jbd2 commit I guess.
There's no reason really to do this in atomic way. I'll fix this in
next version.

On Thu, Oct 17, 2019 at 6:56 PM Theodore Y. Ts'o <tytso@....edu> wrote:
>
> On Tue, Oct 01, 2019 at 12:41:01AM -0700, Harshad Shirwadkar wrote:
> > +
> > +Multiple fast commit blocks are a part of one sub-transaction. To
> > +indicate the last block in a fast commit transaction, fc_flags field
> > +in the last block in every subtransaction is marked with "LAST" (0x1)
> > +flag. A subtransaction is valid only if all the following conditions
> > +are met:
> > +
> > +1) SUBTID of all blocks is either equal to or greater than SUBTID of
> > +   the previous fast commit block.
> > +2) For every sub-transaction, last block is marked with LAST flag.
> > +3) There are no invalid blocks in between.
>
> I'm wondering why we need to support multiple inodes being modified in
> a single transaction.  As we currently have defined what can be done,
> all updates to an inode should be free standing and not dependent on a
> change to another inode, right?  And today, one block only modifies
> one inode.
>
> The only reason why we might want to define a sub-transaction as being
> composed of multiple inodes, which must all be updated in an
> all-or-nothing fashion, is the swap boot inode ioctl, and if that's
> the only one, I wonder if it's worth the extra complexity.
>
> Am I missing anything?
>
>                                         - Ted