linux-kernel - Re: [PATCH v5 15/17] dax: add struct iomap based DAX PMD support

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Date:   Mon, 10 Oct 2016 17:59:17 +0200
From:   Christoph Hellwig <hch@....de>
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@...ts.01.org,
        linux-xfs@...r.kernel.org
Subject: Re: [PATCH v5 15/17] dax: add struct iomap based DAX PMD support

On Fri, Oct 07, 2016 at 03:09:02PM -0600, Ross Zwisler wrote:
> -	if (RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
> +	if ((unsigned long)entry & RADIX_DAX_PMD)

Please introduce a proper inline helper that mask all the possible type
bits out of the radix tree entry, and use them wherever you do the
open cast.

>  restart:
>  	spin_lock_irq(&mapping->tree_lock);
>  	entry = get_unlocked_mapping_entry(mapping, index, &slot);
> +
> +	if (entry) {
> +		if (size_flag & RADIX_DAX_PMD) {
> +			if (!radix_tree_exceptional_entry(entry) ||
> +			    !((unsigned long)entry & RADIX_DAX_PMD)) {
> +				entry = ERR_PTR(-EEXIST);
> +				goto out_unlock;
> +			}
> +		} else { /* trying to grab a PTE entry */
> +			if (radix_tree_exceptional_entry(entry) &&
> +			    ((unsigned long)entry & RADIX_DAX_PMD) &&
> +			    ((unsigned long)entry &
> +			     (RADIX_DAX_HZP|RADIX_DAX_EMPTY))) {

And when we do these cases N times next to each other we should
have a local variable the valid flag bits of entry.