linux-kernel - Re: [PATCH v3 -next 4/9] DMA, CMA: support arbitrary bitmap granularity

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Date:	Wed, 18 Jun 2014 13:48:15 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Nazarewicz <mina86@...a86.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,
	Zhang Yanfei <zhangyanfei@...fujitsu.com>
Subject: Re: [PATCH v3 -next 4/9] DMA, CMA: support arbitrary bitmap
 granularity

On Mon, 16 Jun 2014 14:40:46 +0900 Joonsoo Kim <iamjoonsoo.kim@....com> wrote:

> PPC KVM's CMA area 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.
> 
> ...
>
> --- 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;
>  	unsigned long	*bitmap;
> +	unsigned int order_per_bit; /* Order of pages represented by one bit */
>  	struct mutex	lock;
>  };
>  
> @@ -157,9 +158,37 @@ void __init dma_contiguous_reserve(phys_addr_t limit)
>  
>  static DEFINE_MUTEX(cma_mutex);
>  
> +static unsigned long cma_bitmap_aligned_mask(struct cma *cma, int align_order)
> +{
> +	return (1 << (align_order >> cma->order_per_bit)) - 1;
> +}

Might want a "1UL << ..." here.

> +static unsigned long cma_bitmap_maxno(struct cma *cma)
> +{
> +	return cma->count >> cma->order_per_bit;
> +}
> +
> +static unsigned long cma_bitmap_pages_to_bits(struct cma *cma,
> +						unsigned long pages)
> +{
> +	return ALIGN(pages, 1 << cma->order_per_bit) >> cma->order_per_bit;
> +}

Ditto.  I'm not really sure what the compiler will do in these cases,
but would prefer not to rely on it anyway!


--- a/drivers/base/dma-contiguous.c~dma-cma-support-arbitrary-bitmap-granularity-fix
+++ a/drivers/base/dma-contiguous.c
@@ -160,7 +160,7 @@ static DEFINE_MUTEX(cma_mutex);
 
 static unsigned long cma_bitmap_aligned_mask(struct cma *cma, int align_order)
 {
-	return (1 << (align_order >> cma->order_per_bit)) - 1;
+	return (1UL << (align_order >> cma->order_per_bit)) - 1;
 }
 
 static unsigned long cma_bitmap_maxno(struct cma *cma)
@@ -171,7 +171,7 @@ static unsigned long cma_bitmap_maxno(st
 static unsigned long cma_bitmap_pages_to_bits(struct cma *cma,
 						unsigned long pages)
 {
-	return ALIGN(pages, 1 << cma->order_per_bit) >> cma->order_per_bit;
+	return ALIGN(pages, 1UL << cma->order_per_bit) >> cma->order_per_bit;
 }
 
 static void cma_clear_bitmap(struct cma *cma, unsigned long pfn, int count)
_

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