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SubjectRe: [PATCH] dma_declare_coherent_memory wrong allocation
On Mon, 23 Apr 2007, James Bottomley wrote:

> On Mon, 2007-04-23 at 00:45 +0200, Guennadi Liakhovetski wrote:
> > Right, thinko. How about using his:
> >
> > + int pages = DIV_ROUND_UP(size, PAGE_SIZE);
>
> Actually, no ... this has to be size >> PAGE_SHIFT. The reason being
> that the allocator is designed to allocate pages out of a device memory
> buffer. If the size isn't a multiple of page size, we have to round
> down (we can't allocate the last page if the memory we have is only part
> of a page).
>
> I suppose if you want to catch the unlikely nutcase where size <
> PAGE_SIZE you could
>
> if (unlikely(pages == 0))
> goto out;
>
> > + int bitmap_size = BITS_TO_LONGS(pages) * BYTES_PER_LONG;
>
> This is fine, except the BYTES_PER_LONG. Traditionally, we do this with
> sizeof(long). The only reason to have a #define for it is if it has to
> be used in a macro (the compiler does sizeof() not the preprocessor).
>
> How about just a simple
>
> int bitmap_size = BITS_TO_LONGS(pages) * sizeof(long);

Ok, version 3, small, and hopefully, beautiful:

dma_declare_coherent_memory() allocates a bitmap 1 bit per page, it
calculates the bitmap size based on size of long, but allocates bytes...
Thanks to James Bottomley for clarifications and corrections.

Signed-off-by: G. Liakhovetski <g.liakhovetski@gmx.de>

diff --git a/arch/cris/arch-v32/drivers/pci/dma.c b/arch/cris/arch-v32/drivers/pci/dma.c
index 70d3bf0..832fc63 100644
--- a/arch/cris/arch-v32/drivers/pci/dma.c
+++ b/arch/cris/arch-v32/drivers/pci/dma.c
@@ -76,7 +76,7 @@ int dma_declare_coherent_memory(struct device *dev, dma_addr_t bus_addr,
{
void __iomem *mem_base;
int pages = size >> PAGE_SHIFT;
- int bitmap_size = (pages + 31)/32;
+ int bitmap_size = BITS_TO_LONGS(pages) * sizeof(long);

if ((flags & (DMA_MEMORY_MAP | DMA_MEMORY_IO)) == 0)
goto out;
diff --git a/arch/i386/kernel/pci-dma.c b/arch/i386/kernel/pci-dma.c
index 3ebcea0..30b754f 100644
--- a/arch/i386/kernel/pci-dma.c
+++ b/arch/i386/kernel/pci-dma.c
@@ -77,7 +77,7 @@ int dma_declare_coherent_memory(struct device *dev, dma_addr_t bus_addr,
{
void __iomem *mem_base = NULL;
int pages = size >> PAGE_SHIFT;
- int bitmap_size = (pages + 31)/32;
+ int bitmap_size = BITS_TO_LONGS(pages) * sizeof(long);

if ((flags & (DMA_MEMORY_MAP | DMA_MEMORY_IO)) == 0)
goto out;
-
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