linux-kernel - Re: [PATCH 2/6] fs/direct-io.c: Use DIV_ROUND

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Message-ID: <20080214173850.GC14191@us.ibm.com>
Date:	Thu, 14 Feb 2008 09:38:50 -0800
From:	Nishanth Aravamudan <nacc@...ibm.com>
To:	Julia Lawall <julia@...u.dk>
Cc:	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 2/6] fs/direct-io.c: Use DIV_ROUND_UP

On 14.02.2008 [16:14:33 +0100], Julia Lawall wrote:
> From: Julia Lawall <julia@...u.dk>
> 
> The kernel.h macro DIV_ROUND_UP performs the computation (((n) + (d) - 1) /
> (d)) but is perhaps more readable.
> 
> An extract of the semantic patch that makes this change is as follows:
> (http://www.emn.fr/x-info/coccinelle/)
> 
> // <smpl>
> @haskernel@
> @@
> 
> #include <linux/kernel.h>
> 
> @depends on haskernel@
> expression n,d;
> @@
> 
> (
> - (n + d - 1) / d
> + DIV_ROUND_UP(n,d)
> |
> - (n + (d - 1)) / d
> + DIV_ROUND_UP(n,d)
> )
> 
> @depends on haskernel@
> expression n,d;
> @@
> 
> - DIV_ROUND_UP((n),d)
> + DIV_ROUND_UP(n,d)
> 
> @depends on haskernel@
> expression n,d;
> @@
> 
> - DIV_ROUND_UP(n,(d))
> + DIV_ROUND_UP(n,d)
> // </smpl>
> 
> Signed-off-by: Julia Lawall <julia@...u.dk>
> 
> ---
> 
> diff -u -p a/fs/direct-io.c b/fs/direct-io.c
> --- a/fs/direct-io.c 2008-02-08 08:58:17.000000000 +0100
> +++ b/fs/direct-io.c 2008-02-13 20:58:53.000000000 +0100
> @@ -976,7 +976,7 @@ direct_io_worker(int rw, struct kiocb *i
>  	for (seg = 0; seg < nr_segs; seg++) {
>  		user_addr = (unsigned long)iov[seg].iov_base;
>  		dio->pages_in_io +=
> -			((user_addr+iov[seg].iov_len +PAGE_SIZE-1)/PAGE_SIZE
> +			(DIV_ROUND_UP(user_addr + iov[seg].iov_len, PAGE_SIZE)
>  				- user_addr/PAGE_SIZE);

Is it just me, or does

	((user_addr + iov[seg].iov_len + PAGE_SIZE - 1)/PAGE_SIZE - user_addr/PAGE_SIZE)

not simplify to

	= ((iov[seg].iov_len + PAGE_SIZE - 1)/PAGE_SIZE + user_addr/PAGE_SIZE - user_addr/PAGE_SIZE)

	= ((iov[seg].iov_len + PAGE_SIZE - 1)/PAGE_SIZE)

	= DIV_ROUND_UP(iov[seg].iov_len, PAGE_SIZE)

CMIIW.

Thanks,
Nish

-- 
Nishanth Aravamudan <nacc@...ibm.com>
IBM Linux Technology Center
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