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

Joonsoo Kim
2014-06-16T05:23:25Z

On Thu, Jun 12, 2014 at 12:19:54PM +0200, Michal Nazarewicz wrote:
> 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?

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.