linux-kernel - Re: [PATCH v4 07/12] dax: coordinate locking for offsets in PMD range

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Date:   Fri, 30 Sep 2016 02:44:19 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.com>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-nvdimm@...1.01.org,
        linux-xfs@...r.kernel.org
Subject: Re: [PATCH v4 07/12] dax: coordinate locking for offsets in PMD range

> +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.