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

[Joonsoo Kim]

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 at lge.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;
 	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;
 	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