From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH v4 07/12] dax: coordinate locking for offsets in PMD range
Date: Fri, 30 Sep 2016 02:44:19 -0700
Message-ID: <20160930094419.GA5299@infradead.org>
References: <1475189370-31634-1-git-send-email-ross.zwisler@linux.intel.com>
 <1475189370-31634-8-git-send-email-ross.zwisler@linux.intel.com>
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Cc: linux-kernel@vger.kernel.org, Theodore Ts'o <tytso@mit.edu>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Hellwig <hch@lst.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Chinner <david@fromorbit.com>, Jan Kara <jack@suse.com>,
        Matthew Wilcox <mawilcox@microsoft.com>,
        linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, linux-nvdimm@ml01.01.org,
        linux-xfs@vger.kernel.org
To: Ross Zwisler <ross.zwisler@linux.intel.com>
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> +static pgoff_t dax_entry_start(pgoff_t index, void *entry)
> +{
> +	if (RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
> +		index &= (PMD_MASK >> PAGE_SHIFT);
> +	return index;
> +}
> +
>  static wait_queue_head_t *dax_entry_waitqueue(struct address_space *mapping,
> -					      pgoff_t index)
> +					      pgoff_t entry_start)
>  {
> -	unsigned long hash = hash_long((unsigned long)mapping ^ index,
> +	unsigned long hash = hash_long((unsigned long)mapping ^ entry_start,
>  				       DAX_WAIT_TABLE_BITS);
>  	return wait_table + hash;
>  }

All callers of dax_entry_waitqueue need to calculate entry_start
using this new dax_entry_start helper.  Either we should move the
call to dax_entry_start into this helper.  Or at least use local
variables for in the callers as both of them also fill out a
wait_exceptional_entry_queue structure with it.  Or do both by
letting dax_entry_waitqueue fill out that structure as well.