linux-ext4 - Re: [PATCH 1/2] writeback: avoid double-writing the inode on a lazytime expiration

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Date:   Wed, 25 Mar 2020 02:20:57 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Ext4 Developers List <linux-ext4@...r.kernel.org>,
        linux-f2fs-devel@...ts.sourceforge.net, linux-xfs@...r.kernel.org,
        Eric Biggers <ebiggers@...nel.org>,
        Richard Weinberger <richard@....at>
Subject: Re: [PATCH 1/2] writeback: avoid double-writing the inode on a
 lazytime expiration

>  	spin_unlock(&inode->i_lock);
>  
> -	if (dirty & I_DIRTY_TIME)
> -		mark_inode_dirty_sync(inode);
> +	/* This was a lazytime expiration; we need to tell the file system */
> +	if (dirty & I_DIRTY_TIME_EXPIRED && inode->i_sb->s_op->dirty_inode)
> +		inode->i_sb->s_op->dirty_inode(inode, I_DIRTY_SYNC);

I think this needs a very clear comment explaining why we don't go
through __mark_inode_dirty.

But as said before I'd rather have a new lazytime_expired operation that
makes it very clear what is happening.  We currenly have 4 file systems
(ext4, f2fs, ubifs and xfs) that support lazytime, so this won't really
be a major churn.