The device coherent memory uses the bitmap helper functions, which take an order of PAGE_SIZE, that means the pages size is always a power of 2 as the allocation region. For Example, allocating 33 MB from a 33 MB dma_mem region requires 64MB free memory in that region.
Thus we can change to use bitmap_find_next_zero_area()/bitmap_set()/ bitmap_clear() to present the allocation coherent memory, and reduce the allocation granularity to be one PAGE_SIZE. Moreover from Arnd's description: "I believe that bitmap_allocate_region() was chosen here because it is more efficient than bitmap_find_next_zero_area(), at least that is the explanation given in https://en.wikipedia.org/wiki/Buddy_memory_allocation. It's quite possible that we don't actually care about efficiency of dma_alloc_*() since a) it's supposed to be called very rarely, and b) the overhead of accessing uncached memory is likely higher than the search through a relatively small bitmap". Thus I think we can convert to change the allocation granularity to be one PAGE_SIZE replacing with new bitmap APIs, which will not cause efficiency issue. Signed-off-by: Baolin Wang <baolin.w...@linaro.org> --- drivers/base/dma-coherent.c | 54 +++++++++++++++++++++++-------------------- include/linux/dma-mapping.h | 6 ++--- 2 files changed, 32 insertions(+), 28 deletions(-) diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c index ce19832..4131540 100644 --- a/drivers/base/dma-coherent.c +++ b/drivers/base/dma-coherent.c @@ -143,34 +143,31 @@ void *dma_mark_declared_memory_occupied(struct device *dev, dma_addr_t device_addr, size_t size) { struct dma_coherent_mem *mem = dev->dma_mem; - int order = get_order(size); unsigned long flags; - int pos, err; - - size += device_addr & ~PAGE_MASK; + int start_bit, nbits; if (!mem) return ERR_PTR(-EINVAL); + size += device_addr & ~PAGE_MASK; + nbits = (size + (1UL << PAGE_SHIFT) - 1) >> PAGE_SHIFT; + spin_lock_irqsave(&mem->spinlock, flags); - pos = PFN_DOWN(device_addr - dma_get_device_base(dev, mem)); - err = bitmap_allocate_region(mem->bitmap, pos, order); - if (!err) - mem->avail -= 1 << order; + start_bit = PFN_DOWN(device_addr - dma_get_device_base(dev, mem)); + bitmap_set(mem->bitmap, start_bit, nbits); + mem->avail -= nbits; spin_unlock_irqrestore(&mem->spinlock, flags); - if (err != 0) - return ERR_PTR(err); - return mem->virt_base + (pos << PAGE_SHIFT); + return mem->virt_base + (start_bit << PAGE_SHIFT); } EXPORT_SYMBOL(dma_mark_declared_memory_occupied); static void *__dma_alloc_from_coherent(struct dma_coherent_mem *mem, ssize_t size, dma_addr_t *dma_handle) { - int order = get_order(size); + int nbits = (size + (1UL << PAGE_SHIFT) - 1) >> PAGE_SHIFT; unsigned long flags; - int pageno; + int start_bit, end_bit; void *ret; spin_lock_irqsave(&mem->spinlock, flags); @@ -178,16 +175,22 @@ static void *__dma_alloc_from_coherent(struct dma_coherent_mem *mem, if (unlikely(size > (mem->avail << PAGE_SHIFT))) goto err; - pageno = bitmap_find_free_region(mem->bitmap, mem->size, order); - if (unlikely(pageno < 0)) + start_bit = 0; + end_bit = mem->size; + + start_bit = bitmap_find_next_zero_area(mem->bitmap, end_bit, start_bit, + nbits, 0); + if (start_bit >= end_bit) goto err; + bitmap_set(mem->bitmap, start_bit, nbits); + /* * Memory was found in the coherent area. */ - *dma_handle = mem->device_base + (pageno << PAGE_SHIFT); - ret = mem->virt_base + (pageno << PAGE_SHIFT); - mem->avail -= 1 << order; + *dma_handle = mem->device_base + (start_bit << PAGE_SHIFT); + ret = mem->virt_base + (start_bit << PAGE_SHIFT); + mem->avail -= nbits; spin_unlock_irqrestore(&mem->spinlock, flags); memset(ret, 0, size); return ret; @@ -241,16 +244,17 @@ void *dma_alloc_from_global_coherent(ssize_t size, dma_addr_t *dma_handle) } static int __dma_release_from_coherent(struct dma_coherent_mem *mem, - int order, void *vaddr) + int size, void *vaddr) { if (mem && vaddr >= mem->virt_base && vaddr < (mem->virt_base + (mem->size << PAGE_SHIFT))) { - int page = (vaddr - mem->virt_base) >> PAGE_SHIFT; + int nbits = (size + (1UL << PAGE_SHIFT) - 1) >> PAGE_SHIFT; + int start_bit = (vaddr - mem->virt_base) >> PAGE_SHIFT; unsigned long flags; spin_lock_irqsave(&mem->spinlock, flags); - bitmap_release_region(mem->bitmap, page, order); - mem->avail += 1 << order; + bitmap_clear(mem->bitmap, start_bit, nbits); + mem->avail += nbits; spin_unlock_irqrestore(&mem->spinlock, flags); return 1; } @@ -260,7 +264,7 @@ static int __dma_release_from_coherent(struct dma_coherent_mem *mem, /** * dma_release_from_dev_coherent() - free memory to device coherent memory pool * @dev: device from which the memory was allocated - * @order: the order of pages allocated + * @size: size of release memory area * @vaddr: virtual address of allocated pages * * This checks whether the memory was allocated from the per-device @@ -269,11 +273,11 @@ static int __dma_release_from_coherent(struct dma_coherent_mem *mem, * Returns 1 if we correctly released the memory, or 0 if the caller should * proceed with releasing memory from generic pools. */ -int dma_release_from_dev_coherent(struct device *dev, int order, void *vaddr) +int dma_release_from_dev_coherent(struct device *dev, int size, void *vaddr) { struct dma_coherent_mem *mem = dev_get_coherent_memory(dev); - return __dma_release_from_coherent(mem, order, vaddr); + return __dma_release_from_coherent(mem, size, vaddr); } EXPORT_SYMBOL(dma_release_from_dev_coherent); diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h index f8ab1c0..29ae92e 100644 --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -162,7 +162,7 @@ static inline int is_device_dma_capable(struct device *dev) */ int dma_alloc_from_dev_coherent(struct device *dev, ssize_t size, dma_addr_t *dma_handle, void **ret); -int dma_release_from_dev_coherent(struct device *dev, int order, void *vaddr); +int dma_release_from_dev_coherent(struct device *dev, int size, void *vaddr); int dma_mmap_from_dev_coherent(struct device *dev, struct vm_area_struct *vma, void *cpu_addr, size_t size, int *ret); @@ -174,7 +174,7 @@ int dma_mmap_from_global_coherent(struct vm_area_struct *vma, void *cpu_addr, #else #define dma_alloc_from_dev_coherent(dev, size, handle, ret) (0) -#define dma_release_from_dev_coherent(dev, order, vaddr) (0) +#define dma_release_from_dev_coherent(dev, size, vaddr) (0) #define dma_mmap_from_dev_coherent(dev, vma, vaddr, order, ret) (0) static inline void *dma_alloc_from_global_coherent(ssize_t size, @@ -540,7 +540,7 @@ static inline void dma_free_attrs(struct device *dev, size_t size, BUG_ON(!ops); WARN_ON(irqs_disabled()); - if (dma_release_from_dev_coherent(dev, get_order(size), cpu_addr)) + if (dma_release_from_dev_coherent(dev, size, cpu_addr)) return; if (!ops->free || !cpu_addr) -- 1.7.9.5 _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
