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

Zhang Yanfei
2014-06-12T07:25:25Z

On 06/12/2014 03:08 PM, Minchan Kim wrote:
> 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. ;-)
>

Yeah, not only in this patchset, I saw Joonsoo trying to unify all
kinds of things in the MM. This is great for newbies, IMO.

--
Thanks.
Zhang Yanfei