linux-ext4 - Re: [PATCH v5 4/5] dax: for truncate/hole-punch, do zeroing through the driver if possible

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Date:	Tue, 10 May 2016 16:21:19 +0200
From:	Jan Kara <jack@...e.cz>
To:	Vishal Verma <vishal.l.verma@...el.com>
Cc:	linux-nvdimm@...ts.01.org, linux-fsdevel@...r.kernel.org,
	linux-block@...r.kernel.org, xfs@....sgi.com,
	linux-ext4@...r.kernel.org, linux-mm@...ck.org,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.cz>,
	Jens Axboe <axboe@...com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Jeff Moyer <jmoyer@...hat.com>,
	Boaz Harrosh <boaz@...xistor.com>
Subject: Re: [PATCH v5 4/5] dax: for truncate/hole-punch, do zeroing through
 the driver if possible

On Fri 06-05-16 15:53:10, Vishal Verma wrote:
> +static bool dax_range_is_aligned(struct block_device *bdev,
> +				 struct blk_dax_ctl *dax, unsigned int offset,
> +				 unsigned int length)
> +{
> +	unsigned short sector_size = bdev_logical_block_size(bdev);
> +
> +	if (((u64)dax->addr + offset) % sector_size)
> +		return false;
> +	if (length % sector_size)
> +		return false;

sector_size should better be a power of two so you can save some cycles by
using & instead of %.

> @@ -1240,11 +1254,17 @@ int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
>  			.size = PAGE_SIZE,
>  		};
>  
> -		if (dax_map_atomic(bdev, &dax) < 0)
> -			return PTR_ERR(dax.addr);
> -		clear_pmem(dax.addr + offset, length);
> -		wmb_pmem();
> -		dax_unmap_atomic(bdev, &dax);
> +		if (dax_range_is_aligned(bdev, &dax, offset, length))
> +			return blkdev_issue_zeroout(bdev, dax.sector,
> +					length / bdev_logical_block_size(bdev),
> +					GFP_NOFS, true);

This is actually wrong. blkdev_issue_zeroout() expects length to be simply
in units of 512-bytes. So you need length >> 9 here.

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