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

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Date:	Sat, 21 Jan 2012 00:41:56 +0900
From:	Akinobu Mita <akinobu.mita@...il.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Jeremy Fitzhardinge Jeremy Fitzhardinge <jeremy@...p.org>,
	xen-devel@...ts.xensource.com,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] xen-blkfront: use bitmap_set() and bitmap_clear()

2012/1/21 Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>:
> 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'?

'end' is the index of the last bit to clear.  But the last argument of
bitmap_clear() is the number of bits to clear.  So I think 'nr' is correct.

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

Sorry I didn't do runtime test.

>>               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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