linux-kernel - Re: [PATCH v7 05/14] ext4, dax: introduce ext4_dax

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Message-ID: <20180329154035.lvsepjvt6vcplshw@quack2.suse.cz>
Date:   Thu, 29 Mar 2018 17:40:35 +0200
From:   Jan Kara <jack@...e.cz>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     linux-nvdimm@...ts.01.org, Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org, Jan Kara <jack@...e.cz>,
        david@...morbit.com, hch@....de, linux-fsdevel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 05/14] ext4, dax: introduce ext4_dax_aops

On Wed 21-03-18 15:57:37, Dan Williams wrote:
> In preparation for the dax implementation to start associating dax pages
> to inodes via page->mapping, we need to provide a 'struct
> address_space_operations' instance for dax. Otherwise, direct-I/O
> triggers incorrect page cache assumptions and warnings.
> 
> Cc: "Theodore Ts'o" <tytso@....edu>
> Cc: Andreas Dilger <adilger.kernel@...ger.ca>
> Cc: linux-ext4@...r.kernel.org
> Cc: Jan Kara <jack@...e.cz>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>

Looks good, just one nit below.

> @@ -3946,6 +3961,13 @@ static const struct address_space_operations ext4_da_aops = {
>  	.error_remove_page	= generic_error_remove_page,
>  };
>  
> +static const struct address_space_operations ext4_dax_aops = {
> +	.direct_IO		= ext4_direct_IO,

So ext4_direct_IO() for IS_DAX() files will just bail out. So could you
just provide ext4_dax_direct_IO() which will bail out and use it here? With
a similar comment as in xfs_vm_direct_IO() that open still needs this
method set... Thanks!

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR