linux-kernel - Re: [PATCH v2 05/10] DMA, CMA: support arbitrary bitmap granularity

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Date:	Mon, 16 Jun 2014 14:23:25 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Michal Nazarewicz <mina86@...a86.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Minchan Kim <minchan@...nel.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Gleb Natapov <gleb@...nel.org>, Alexander Graf <agraf@...e.de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	kvm@...r.kernel.org, kvm-ppc@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 05/10] DMA, CMA: support arbitrary bitmap granularity

On Thu, Jun 12, 2014 at 12:19:54PM +0200, Michal Nazarewicz wrote:
> On Thu, Jun 12 2014, Joonsoo Kim <iamjoonsoo.kim@....com> wrote:
> > ppc kvm's cma region management requires arbitrary bitmap granularity,
> > since they want to reserve very large memory and manage this region
> > with bitmap that one bit for several pages to reduce management overheads.
> > So support arbitrary bitmap granularity for following generalization.
> >
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> 
> Acked-by: Michal Nazarewicz <mina86@...a86.com>
> 
> > diff --git a/drivers/base/dma-contiguous.c b/drivers/base/dma-contiguous.c
> > index bc4c171..9bc9340 100644
> > --- a/drivers/base/dma-contiguous.c
> > +++ b/drivers/base/dma-contiguous.c
> > @@ -38,6 +38,7 @@ struct cma {
> >  	unsigned long	base_pfn;
> >  	unsigned long	count;
> 
> Have you considered replacing count with maxno?

No, I haven't.
I think that count is better than maxno, since it represent number of
pages in this region.

> 
> >  	unsigned long	*bitmap;
> > +	int order_per_bit; /* Order of pages represented by one bit */
> 
> I'd make it unsigned.

Will fix it.

> >  	struct mutex	lock;
> >  };
> >  
> > +static void clear_cma_bitmap(struct cma *cma, unsigned long pfn, int
> > count)
> 
> For consistency cma_clear_bitmap would make more sense I think.  On the
> other hand, you're just moving stuff around so perhaps renaming the
> function at this point is not worth it any more.

Will fix it.

> > +{
> > +	unsigned long bitmapno, nr_bits;
> > +
> > +	bitmapno = (pfn - cma->base_pfn) >> cma->order_per_bit;
> > +	nr_bits = cma_bitmap_pages_to_bits(cma, count);
> > +
> > +	mutex_lock(&cma->lock);
> > +	bitmap_clear(cma->bitmap, bitmapno, nr_bits);
> > +	mutex_unlock(&cma->lock);
> > +}
> > +
> >  static int __init cma_activate_area(struct cma *cma)
> >  {
> > -	int bitmap_size = BITS_TO_LONGS(cma->count) * sizeof(long);
> > +	int bitmap_maxno = cma_bitmap_maxno(cma);
> > +	int bitmap_size = BITS_TO_LONGS(bitmap_maxno) * sizeof(long);
> >  	unsigned long base_pfn = cma->base_pfn, pfn = base_pfn;
> >  	unsigned i = cma->count >> pageblock_order;
> >  	struct zone *zone;
> 
> bitmap_maxno is never used again, perhaps:
> 
> +	int bitmap_size = BITS_TO_LONGS(cma_bitmap_maxno(cma)) * sizeof(long);
> 
> instead? Up to you.

Okay!!

Thanks.
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