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

Minchan Kim
2014-06-12T07:08:11Z

On Thu, Jun 12, 2014 at 12:21:42PM +0900, Joonsoo Kim 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: Minchan Kim <minchan@kernel.org>

Just a nit below.

>
> 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;
> unsigned long *bitmap;
> + int order_per_bit; /* Order of pages represented by one bit */
> struct mutex lock;
> };
>
> @@ -157,9 +158,38 @@ 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;
> +}
> +
> +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;
> +}
> +
> +static void clear_cma_bitmap(struct cma *cma, unsigned long pfn, int count)
> +{
> + 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;
> @@ -221,6 +251,7 @@ core_initcall(cma_init_reserved_areas);
> * @base: Base address of the reserved area optional, use 0 for any
> * @limit: End address of the reserved memory (optional, 0 for any).
> * @alignment: Alignment for the contiguous memory area, should be power of 2
> + * @order_per_bit: Order of pages represented by one bit on bitmap.
> * @res_cma: Pointer to store the created cma region.
> * @fixed: hint about where to place the reserved area
> *
> @@ -235,7 +266,7 @@ core_initcall(cma_init_reserved_areas);
> */
> static int __init __dma_contiguous_reserve_area(phys_addr_t size,
> phys_addr_t base, phys_addr_t limit,
> - phys_addr_t alignment,
> + phys_addr_t alignment, int order_per_bit,
> struct cma **res_cma, bool fixed)
> {
> struct cma *cma = &cma_areas[cma_area_count];
> @@ -269,6 +300,8 @@ static int __init __dma_contiguous_reserve_area(phys_addr_t size,
> base = ALIGN(base, alignment);
> size = ALIGN(size, alignment);
> limit &= ~(alignment - 1);
> + /* size should be aligned with order_per_bit */
> + BUG_ON(!IS_ALIGNED(size >> PAGE_SHIFT, 1 << order_per_bit));
>
> /* Reserve memory */
> if (base && fixed) {
> @@ -294,6 +327,7 @@ static int __init __dma_contiguous_reserve_area(phys_addr_t size,
> */
> cma->base_pfn = PFN_DOWN(base);
> cma->count = size >> PAGE_SHIFT;
> + cma->order_per_bit = order_per_bit;
> *res_cma = cma;
> cma_area_count++;
>
> @@ -313,7 +347,7 @@ int __init dma_contiguous_reserve_area(phys_addr_t size, phys_addr_t base,
> {
> int ret;
>
> - ret = __dma_contiguous_reserve_area(size, base, limit, 0,
> + ret = __dma_contiguous_reserve_area(size, base, limit, 0, 0,
> res_cma, fixed);
> if (ret)
> return ret;
> @@ -324,13 +358,6 @@ int __init dma_contiguous_reserve_area(phys_addr_t size, phys_addr_t base,
> return 0;
> }
>
> -static void clear_cma_bitmap(struct cma *cma, unsigned long pfn, int count)
> -{
> - mutex_lock(&cma->lock);
> - bitmap_clear(cma->bitmap, pfn - cma->base_pfn, count);
> - mutex_unlock(&cma->lock);
> -}
> -
> /**
> * dma_alloc_from_contiguous() - allocate pages from contiguous area
> * @dev: Pointer to device for which the allocation is performed.
> @@ -345,7 +372,8 @@ static void clear_cma_bitmap(struct cma *cma, unsigned long pfn, int count)
> static struct page *__dma_alloc_from_contiguous(struct cma *cma, int count,
> unsigned int align)
> {
> - unsigned long mask, pfn, pageno, start = 0;
> + unsigned long mask, pfn, start = 0;
> + unsigned long bitmap_maxno, bitmapno, nr_bits;

Just Nit: bitmap_maxno, bitmap_no or something consistent.
I know you love consistent when I read description in first patch
in this patchset. ;-)

> struct page *page = NULL;
> int ret;
>
> @@ -358,18 +386,19 @@ static struct page *__dma_alloc_from_contiguous(struct cma *cma, int count,
> if (!count)
> return NULL;
>
> - mask = (1 << align) - 1;
> -
> + mask = cma_bitmap_aligned_mask(cma, align);
> + bitmap_maxno = cma_bitmap_maxno(cma);
> + nr_bits = cma_bitmap_pages_to_bits(cma, count);
>
> for (;;) {
> mutex_lock(&cma->lock);
> - pageno = bitmap_find_next_zero_area(cma->bitmap, cma->count,
> - start, count, mask);
> - if (pageno >= cma->count) {
> + bitmapno = bitmap_find_next_zero_area(cma->bitmap,
> + bitmap_maxno, start, nr_bits, mask);
> + if (bitmapno >= bitmap_maxno) {
> mutex_unlock(&cma->lock);
> break;
> }
> - bitmap_set(cma->bitmap, pageno, count);
> + bitmap_set(cma->bitmap, bitmapno, nr_bits);
> /*
> * It's safe to drop the lock here. We've marked this region for
> * our exclusive use. If the migration fails we will take the
> @@ -377,7 +406,7 @@ static struct page *__dma_alloc_from_contiguous(struct cma *cma, int count,
> */
> mutex_unlock(&cma->lock);
>
> - pfn = cma->base_pfn + pageno;
> + pfn = cma->base_pfn + (bitmapno << cma->order_per_bit);
> mutex_lock(&cma_mutex);
> ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA);
> mutex_unlock(&cma_mutex);
> @@ -392,7 +421,7 @@ static struct page *__dma_alloc_from_contiguous(struct cma *cma, int count,
> pr_debug("%s(): memory range at %p is busy, retrying\n",
> __func__, pfn_to_page(pfn));
> /* try again with a bit different memory target */
> - start = pageno + mask + 1;
> + start = bitmapno + mask + 1;
> }
>
> pr_debug("%s(): returned %p\n", __func__, page);
> --
> 1.7.9.5

--
Kind regards,
Minchan Kim