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Date: Wed, 3 Jan 2018 17:05:03 +0100
From: Jan Kara <jack@suse.cz>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jan Kara <jack@suse.cz>,
        Matthew Wilcox <mawilcox@microsoft.com>,
        linux-nvdimm@lists.01.org, linux-xfs <linux-xfs@vger.kernel.org>,
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        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Ross Zwisler <ross.zwisler@linux.intel.com>,
        Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v4 11/18] fs, dax: introduce DEFINE_FSDAX_AOPS
Message-ID: <20180103160503.GM4911@quack2.suse.cz>
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On Tue 02-01-18 12:21:28, Dan Williams wrote:
> >> +EXPORT_SYMBOL(dax_set_page_dirty);
> >> +EXPORT_SYMBOL(dax_direct_IO);
> >> +EXPORT_SYMBOL(dax_writepage);
> >> +EXPORT_SYMBOL(dax_readpage);
> >> +EXPORT_SYMBOL(dax_readpages);
> >> +EXPORT_SYMBOL(dax_write_begin);
> >> +EXPORT_SYMBOL(dax_write_end);
> >> +EXPORT_SYMBOL(dax_invalidatepage);
> >
> > Exporting all these symbols to modules isn't exactly free.  Are you sure it
> > doesn't make more sense to put tests for dax in the existing aops?
> >
> 
> I'd rather have just one global fs_dax_aops instance that all
> filesystems could reference, but ->writepages() is fundamentally an
> address_space_operation. Until we can rework that I'd prefer the
> overhead of the extra exports than sprinkling more IS_DAX checks
> around.

Just for record I agree with what Dave said about this patch. Generic
address_space_operations are not how aops are commonly defined by
filesystems. Just create one structure for each fs as Dave suggested.

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