linux-ext4 - Re: [PATCH 3/7] dax: remove buffer_size

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Message-ID: <20160816091357.GC27284@quack2.suse.cz>
Date:	Tue, 16 Aug 2016 11:13:57 +0200
From:	Jan Kara <jack@...e.cz>
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>,
	Dan Williams <dan.j.williams@...el.com>,
	Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.com>,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-nvdimm@...ts.01.org
Subject: Re: [PATCH 3/7] dax: remove buffer_size_valid()

On Mon 15-08-16 13:09:14, Ross Zwisler wrote:
> Now that all our supported filesystems (ext2, ext4 and XFS) all properly
> set bh.b_size when we call get_block() for a hole, rely on that value and
> remove the buffer_size_valid() sanity check.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>

Looks good. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/dax.c | 22 +---------------------
>  1 file changed, 1 insertion(+), 21 deletions(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index 993dc6f..8030f93 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -121,19 +121,6 @@ static bool buffer_written(struct buffer_head *bh)
>  	return buffer_mapped(bh) && !buffer_unwritten(bh);
>  }
>  
> -/*
> - * When ext4 encounters a hole, it returns without modifying the buffer_head
> - * which means that we can't trust b_size.  To cope with this, we set b_state
> - * to 0 before calling get_block and, if any bit is set, we know we can trust
> - * b_size.  Unfortunate, really, since ext4 knows precisely how long a hole is
> - * and would save us time calling get_block repeatedly.
> - */
> -static bool buffer_size_valid(struct buffer_head *bh)
> -{
> -	return bh->b_state != 0;
> -}
> -
> -
>  static sector_t to_sector(const struct buffer_head *bh,
>  		const struct inode *inode)
>  {
> @@ -175,8 +162,6 @@ static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
>  				rc = get_block(inode, block, bh, rw == WRITE);
>  				if (rc)
>  					break;
> -				if (!buffer_size_valid(bh))
> -					bh->b_size = 1 << blkbits;
>  				bh_max = pos - first + bh->b_size;
>  				bdev = bh->b_bdev;
>  				/*
> @@ -1010,12 +995,7 @@ int dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
>  
>  	bdev = bh.b_bdev;
>  
> -	/*
> -	 * If the filesystem isn't willing to tell us the length of a hole,
> -	 * just fall back to PTEs.  Calling get_block 512 times in a loop
> -	 * would be silly.
> -	 */
> -	if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE) {
> +	if (bh.b_size < PMD_SIZE) {
>  		dax_pmd_dbg(&bh, address, "allocated block too small");
>  		return VM_FAULT_FALLBACK;
>  	}
> -- 
> 2.9.0
> 
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR
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