Hello,

On Friday, August 24, 2012 1:52 PM Hiroshi Doyu wrote:

Konrad Rzeszutek Wilk [off-list ref] wrote @ Fri, 24 Aug 2012 13:13:23 +0200:

quoted

On Fri, Aug 24, 2012 at 11:29:02AM +0300, Hiroshi Doyu wrote:

quoted

struct page **pages is necessary to align with non atomic path in
__iommu_get_pages(). atomic_pool() has the intialized **pages instead
of just *page.

Signed-off-by: Hiroshi Doyu <redacted>
---
 arch/arm/mm/dma-mapping.c |   17 +++++++++++++----
 1 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 601da7a..b14ee64 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c

@@ -296,7 +296,7 @@ struct dma_pool {
 	unsigned long *bitmap;
 	unsigned long nr_pages;
 	void *vaddr;
-	struct page *page;
+	struct page **pages;
 };

 static struct dma_pool atomic_pool = {

@@ -335,12 +335,16 @@ static int __init atomic_pool_init(void)
 	unsigned long nr_pages = pool->size >> PAGE_SHIFT;
 	unsigned long *bitmap;
 	struct page *page;
+	struct page **pages;
 	void *ptr;
 	int bitmap_size = BITS_TO_LONGS(nr_pages) * sizeof(long);
+	size_t size = nr_pages * sizeof(struct page *);

-	bitmap = kzalloc(bitmap_size, GFP_KERNEL);
+	size += bitmap_size;
+	bitmap = kzalloc(size, GFP_KERNEL);
 	if (!bitmap)
 		goto no_bitmap;
+	pages = (void *)bitmap + bitmap_size;

So you stuck a bitmap field in front of the array then?
Why not just define a structure where this is clearly defined
instead of doing the casting.

I just wanted to allocate only once for the members "pool->bitmap" and
"pool->pages" at once. Since the size of a whole bitmap isn't known in
advance, I couldn't find any fixed type for this bitmap, which pointer
can be shifted without casting. IOW, they are variable length.

IMHO it is better to avoid any non-trivial things in generic arch code. Merging
those 2 allocations doesn't save any significant bit of memory and might confuse
someone. Better just allocate them separately.

Best regards
-- 
Marek Szyprowski
Samsung Poland R&D Center