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Subject: Re: [PATCH 2/2] block: use DAX for partition table reads
To: Dan Williams <dan.j.williams@intel.com>, <linux-block@vger.kernel.org>
References: <20160129151835.18752.9423.stgit@dwillia2-desk3.amr.corp.intel.com>
 <20160129151846.18752.48460.stgit@dwillia2-desk3.amr.corp.intel.com>
CC: <linux-nvdimm@ml01.01.org>, Dave Chinner <david@fromorbit.com>,
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        Matthew Wilcox <willy@linux.intel.com>,
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        Ross Zwisler <ross.zwisler@linux.intel.com>
From: Jens Axboe <axboe@fb.com>
Message-ID: <56ABA561.9070606@fb.com>
Date: Fri, 29 Jan 2016 10:46:09 -0700
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On 01/29/2016 08:18 AM, Dan Williams wrote:
> +unsigned char *read_dev_sector(struct block_device *bdev, sector_t n, Sector *p)
> +{
>   	struct page *page;
>
> -	page = read_mapping_page(mapping, (pgoff_t)(n >> (PAGE_CACHE_SHIFT-9)),
> -				 NULL);
> +	/* don't populate page cache for dax capable devices */
> +	if (IS_DAX(bdev->bd_inode))
> +		page = read_dax_sector(bdev, n);
> +	else
> +		page = read_pagecache_sector(bdev, n);
> +

Fall back to non-dax, if dax fails?

> +struct page *read_dax_sector(struct block_device *bdev, sector_t n)
> +{
> +	struct page *page = __page_cache_alloc(GFP_KERNEL | __GFP_COLD);

Why isn't that just alloc_pages()?

-- 
Jens Axboe