linux-ext4 - Re: [PATCH v2 05/12] jbd2: fast-commit commit path new APIs

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Message-ID: <20190812180106.GB28705@mit.edu>
Date:   Mon, 12 Aug 2019 14:01:06 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     harshad shirwadkar <harshadshirwadkar@...il.com>
Cc:     Andreas Dilger <adilger@...ger.ca>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v2 05/12] jbd2: fast-commit commit path new APIs

On Mon, Aug 12, 2019 at 10:41:48AM -0700, harshad shirwadkar wrote:
> I see, so you mean each fsync() call will result in exactly one inode
> to be committed (the inode on which fsync was called), right? I agree
> this doesn't need to go through JBD2 but we need a mechanism to inform
> JBD2 about this fast commit since JBD2 maintains sub-transaction ID.
> JBD2 will in turn need to make sure that a subtid was allocated for
> such a fast commit and it was incremented once the fast commit was
> successful as well.

Why does JBD2 need to maintain the sub-transaction ID?  We can only
have a single fast commit happening at a time, and while a fast commit
is happening we can't allow a full commit from happening (or vice
versa).  So we need a mutex which enforces this, the transaction id
can just be a field in the transaction structure.

Cheers,

					- Ted