linux-kernel - Re: [PATCH] xen-blkfront: use bitmap_set() and bitmap

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Date:	Fri, 20 Jan 2012 10:28:19 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Akinobu Mita <akinobu.mita@...il.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	xen-devel@...ts.xensource.com,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] xen-blkfront: use bitmap_set() and bitmap_clear()

On Sat, Jan 21, 2012 at 12:15:26AM +0900, Akinobu Mita wrote:
> Use bitmap_set and bitmap_clear rather than modifying individual bits
> in a memory region.
> 
> Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
> Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Cc: xen-devel@...ts.xensource.com
> Cc: virtualization@...ts.linux-foundation.org
> ---
>  drivers/block/xen-blkfront.c |    7 +++----
>  1 files changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 2f22874..619868d 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -43,6 +43,7 @@
>  #include <linux/slab.h>
>  #include <linux/mutex.h>
>  #include <linux/scatterlist.h>
> +#include <linux/bitmap.h>
>  
>  #include <xen/xen.h>
>  #include <xen/xenbus.h>
> @@ -177,8 +178,7 @@ static int xlbd_reserve_minors(unsigned int minor, unsigned int nr)
>  
>  	spin_lock(&minor_lock);
>  	if (find_next_bit(minors, end, minor) >= end) {
> -		for (; minor < end; ++minor)
> -			__set_bit(minor, minors);
> +		bitmap_set(minors, minor, nr);

Hm, I would have thought the last argument should have been 'end'?

Did you test this patch with a large amount of minors?

>  		rc = 0;
>  	} else
>  		rc = -EBUSY;
> @@ -193,8 +193,7 @@ static void xlbd_release_minors(unsigned int minor, unsigned int nr)
>  
>  	BUG_ON(end > nr_minors);
>  	spin_lock(&minor_lock);
> -	for (; minor < end; ++minor)
> -		__clear_bit(minor, minors);
> +	bitmap_clear(minors,  minor, nr);

Ditto.
>  	spin_unlock(&minor_lock);
>  }
>  
> -- 
> 1.7.4.4
> 
> --
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