[1/2] dma-coherent: Add one parameter to save available coherent memory

Message ID c5765cf69bf222757463ba2653ac760b42b785e6.1527745258.git.baolin.wang@linaro.org
State New
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  • [1/2] dma-coherent: Add one parameter to save available coherent memory
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Commit Message

Baolin Wang May 31, 2018, 5:55 a.m.
It is incorrect to use mem->size to valid if there are enough coherent
memory to allocate in __dma_alloc_from_coherent(), since some devices
may mark some occupied coherent memory by dma_mark_declared_memory_occupied().

So we can introduce one 'avail' parameter to save the available device
coherent memory, to valid if we have enough coherent memory for the device
to allocate.

Signed-off-by: Baolin Wang <baolin.wang@linaro.org>

---
 drivers/base/dma-coherent.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

-- 
1.7.9.5

Comments

Robin Murphy May 31, 2018, 5:25 p.m. | #1
On 31/05/18 06:55, Baolin Wang wrote:
> It is incorrect to use mem->size to valid if there are enough coherent

> memory to allocate in __dma_alloc_from_coherent(), since some devices

> may mark some occupied coherent memory by dma_mark_declared_memory_occupied().

> 

> So we can introduce one 'avail' parameter to save the available device

> coherent memory, to valid if we have enough coherent memory for the device

> to allocate.


We already have dma_mem->size stored for other reasons, so there's 
little harm in using it for a rough sanity check to short-circuit the 
odd allocation which cannot possibly succeed, but adding machinery 
purely for the sake an ever-so-slightly more accurate, but still far 
from exhaustive, check doesn't really seem worth it.

Even if size <= dma_mem->avail there's still no guarantee that the 
allocation will actually succeed, so what benefit does the explicit 
accounting provide?

Robin.

> Signed-off-by: Baolin Wang <baolin.wang@linaro.org>

> ---

>   drivers/base/dma-coherent.c |   11 +++++++++--

>   1 file changed, 9 insertions(+), 2 deletions(-)

> 

> diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c

> index 597d408..ce19832 100644

> --- a/drivers/base/dma-coherent.c

> +++ b/drivers/base/dma-coherent.c

> @@ -18,6 +18,7 @@ struct dma_coherent_mem {

>   	unsigned long	*bitmap;

>   	spinlock_t	spinlock;

>   	bool		use_dev_dma_pfn_offset;

> +	int		avail;

>   };

>   

>   static struct dma_coherent_mem *dma_coherent_default_memory __ro_after_init;

> @@ -73,6 +74,7 @@ static int dma_init_coherent_memory(

>   	dma_mem->device_base = device_addr;

>   	dma_mem->pfn_base = PFN_DOWN(phys_addr);

>   	dma_mem->size = pages;

> +	dma_mem->avail = pages;

>   	dma_mem->flags = flags;

>   	spin_lock_init(&dma_mem->spinlock);

>   

> @@ -141,6 +143,7 @@ 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;

>   

> @@ -151,7 +154,9 @@ void *dma_mark_declared_memory_occupied(struct device *dev,

>   

>   	spin_lock_irqsave(&mem->spinlock, flags);

>   	pos = PFN_DOWN(device_addr - dma_get_device_base(dev, mem));

> -	err = bitmap_allocate_region(mem->bitmap, pos, get_order(size));

> +	err = bitmap_allocate_region(mem->bitmap, pos, order);

> +	if (!err)

> +		mem->avail -= 1 << order;

>   	spin_unlock_irqrestore(&mem->spinlock, flags);

>   

>   	if (err != 0)

> @@ -170,7 +175,7 @@ static void *__dma_alloc_from_coherent(struct dma_coherent_mem *mem,

>   

>   	spin_lock_irqsave(&mem->spinlock, flags);

>   

> -	if (unlikely(size > (mem->size << PAGE_SHIFT)))

> +	if (unlikely(size > (mem->avail << PAGE_SHIFT)))

>   		goto err;

>   

>   	pageno = bitmap_find_free_region(mem->bitmap, mem->size, order);

> @@ -182,6 +187,7 @@ static void *__dma_alloc_from_coherent(struct dma_coherent_mem *mem,

>   	 */

>   	*dma_handle = mem->device_base + (pageno << PAGE_SHIFT);

>   	ret = mem->virt_base + (pageno << PAGE_SHIFT);

> +	mem->avail -= 1 << order;

>   	spin_unlock_irqrestore(&mem->spinlock, flags);

>   	memset(ret, 0, size);

>   	return ret;

> @@ -244,6 +250,7 @@ static int __dma_release_from_coherent(struct dma_coherent_mem *mem,

>   

>   		spin_lock_irqsave(&mem->spinlock, flags);

>   		bitmap_release_region(mem->bitmap, page, order);

> +		mem->avail += 1 << order;

>   		spin_unlock_irqrestore(&mem->spinlock, flags);

>   		return 1;

>   	}

>
Baolin Wang June 3, 2018, 2:12 a.m. | #2
On 1 June 2018 at 01:25, Robin Murphy <robin.murphy@arm.com> wrote:
> On 31/05/18 06:55, Baolin Wang wrote:

>>

>> It is incorrect to use mem->size to valid if there are enough coherent

>> memory to allocate in __dma_alloc_from_coherent(), since some devices

>> may mark some occupied coherent memory by

>> dma_mark_declared_memory_occupied().

>>

>> So we can introduce one 'avail' parameter to save the available device

>> coherent memory, to valid if we have enough coherent memory for the device

>> to allocate.

>

>

> We already have dma_mem->size stored for other reasons, so there's little

> harm in using it for a rough sanity check to short-circuit the odd

> allocation which cannot possibly succeed, but adding machinery purely for

> the sake an ever-so-slightly more accurate, but still far from exhaustive,

> check doesn't really seem worth it.

>

> Even if size <= dma_mem->avail there's still no guarantee that the

> allocation will actually succeed, so what benefit does the explicit

> accounting provide?

>


Yes, it can not guarantee one successful allocation, but it can avoid
some redundant bitmap operation and reducing the preempt-disable time
if we have not enough memory by checking the actual available coherent
memory. By the way, I think we should also add check in
dma_mark_declared_memory_occupied() and __dma_mmap_from_coherent().

-- 
Baolin.wang
Best Regards

Patch

diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c
index 597d408..ce19832 100644
--- a/drivers/base/dma-coherent.c
+++ b/drivers/base/dma-coherent.c
@@ -18,6 +18,7 @@  struct dma_coherent_mem {
 	unsigned long	*bitmap;
 	spinlock_t	spinlock;
 	bool		use_dev_dma_pfn_offset;
+	int		avail;
 };
 
 static struct dma_coherent_mem *dma_coherent_default_memory __ro_after_init;
@@ -73,6 +74,7 @@  static int dma_init_coherent_memory(
 	dma_mem->device_base = device_addr;
 	dma_mem->pfn_base = PFN_DOWN(phys_addr);
 	dma_mem->size = pages;
+	dma_mem->avail = pages;
 	dma_mem->flags = flags;
 	spin_lock_init(&dma_mem->spinlock);
 
@@ -141,6 +143,7 @@  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;
 
@@ -151,7 +154,9 @@  void *dma_mark_declared_memory_occupied(struct device *dev,
 
 	spin_lock_irqsave(&mem->spinlock, flags);
 	pos = PFN_DOWN(device_addr - dma_get_device_base(dev, mem));
-	err = bitmap_allocate_region(mem->bitmap, pos, get_order(size));
+	err = bitmap_allocate_region(mem->bitmap, pos, order);
+	if (!err)
+		mem->avail -= 1 << order;
 	spin_unlock_irqrestore(&mem->spinlock, flags);
 
 	if (err != 0)
@@ -170,7 +175,7 @@  static void *__dma_alloc_from_coherent(struct dma_coherent_mem *mem,
 
 	spin_lock_irqsave(&mem->spinlock, flags);
 
-	if (unlikely(size > (mem->size << PAGE_SHIFT)))
+	if (unlikely(size > (mem->avail << PAGE_SHIFT)))
 		goto err;
 
 	pageno = bitmap_find_free_region(mem->bitmap, mem->size, order);
@@ -182,6 +187,7 @@  static void *__dma_alloc_from_coherent(struct dma_coherent_mem *mem,
 	 */
 	*dma_handle = mem->device_base + (pageno << PAGE_SHIFT);
 	ret = mem->virt_base + (pageno << PAGE_SHIFT);
+	mem->avail -= 1 << order;
 	spin_unlock_irqrestore(&mem->spinlock, flags);
 	memset(ret, 0, size);
 	return ret;
@@ -244,6 +250,7 @@  static int __dma_release_from_coherent(struct dma_coherent_mem *mem,
 
 		spin_lock_irqsave(&mem->spinlock, flags);
 		bitmap_release_region(mem->bitmap, page, order);
+		mem->avail += 1 << order;
 		spin_unlock_irqrestore(&mem->spinlock, flags);
 		return 1;
 	}