Re: [Xen-devel] [PATCH] xen-blkfront: use bitmap_set() and bitmap_clear()

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Sat, Jan 21, 2012 at 12:41:56AM +0900, Akinobu Mita wrote:
> 2012/1/21 Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>:
> > 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@xxxxxxxxx>
> >> Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
> >> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> >> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
> >> Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
> >> ---
> >>  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.

Ah, I see it.
> 
> > Did you test this patch with a large amount of minors?
> 
> Sorry I didn't do runtime test.

Please do.

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