From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH v7 11/22] fs: new infrastructure for writeback error
 handling and reporting
Date: Tue, 20 Jun 2017 05:34:33 -0700
Message-ID: <20170620123433.GB19781@infradead.org>
References: <20170616193427.13955-1-jlayton@redhat.com>
 <20170616193427.13955-12-jlayton@redhat.com>
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Cc: Andrew Morton <akpm@linux-foundation.org>,
	Al Viro <viro@ZenIV.linux.org.uk>, Jan Kara <jack@suse.cz>,
	tytso@mit.edu, axboe@kernel.dk, mawilcox@microsoft.com,
	ross.zwisler@linux.intel.com, corbet@lwn.net,
	Chris Mason <clm@fb.com>, Josef Bacik <jbacik@fb.com>,
	David Sterba <dsterba@suse.com>,
	"Darrick J . Wong" <darrick.wong@oracle.com>,
	Carlos Maiolino <cmaiolino@redhat.com>,
	Eryu Guan <eguan@redhat.com>, David Howells <dhowells@redhat.com>,
	Christoph Hellwig <hch@infradead.org>,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org,
	linux-btrfs@vger.kernel.org, linux-block@vger.kernel.org
To: Jeff Layton <jlayton@redhat.com>
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> @@ -393,6 +394,7 @@ struct address_space {
>  	gfp_t			gfp_mask;	/* implicit gfp mask for allocations */
>  	struct list_head	private_list;	/* ditto */
>  	void			*private_data;	/* ditto */
> +	errseq_t		wb_err;
>  } __attribute__((aligned(sizeof(long))));
>  	/*
>  	 * On most architectures that alignment is already the case; but
> @@ -847,6 +849,7 @@ struct file {
>  	 * Must not be taken from IRQ context.
>  	 */
>  	spinlock_t		f_lock;
> +	errseq_t		f_wb_err;
>  	atomic_long_t		f_count;
>  	unsigned int 		f_flags;
>  	fmode_t			f_mode;

Did you check the sizes of the structure before and after?
These places don't look like holes in the packing, but there probably
are some available.

> +static inline int filemap_check_wb_err(struct address_space *mapping, errseq_t since)

Overly long line here (the patch has a few more)

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