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

Michal Nazarewicz
2014-06-12T10:20:03Z

On Thu, Jun 12 2014, Joonsoo Kim <iamjoonsoo.kim@lge.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@lge.com>

Acked-by: Michal Nazarewicz <mina86@mina86.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?

> unsigned long *bitmap;
> + int order_per_bit; /* Order of pages represented by one bit */

I'd make it unsigned.

> 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.

> +{
> + 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.

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