Re: [PATCH] x86: avoid unnecessary low zone allocation in AMD IOMMU's alloc_coherent

From: Joerg Roedel
Date: Thu Sep 11 2008 - 05:11:15 EST

On Wed, Sep 10, 2008 at 11:45:34PM +0900, FUJITA Tomonori wrote:
> On Wed, 10 Sep 2008 16:38:18 +0200
> Joerg Roedel <joro@xxxxxxxxxx> wrote:
> > Ok, thats a valid point. I queue your patch with the AMD IOMMU updates
> > for 2.6.28. Thanks.
> Ingo already has queued it his tree, I think.

I asked Ingo to remove it from his tree to avoid merge conflicts with
updates I am currently preparing. Here is the patch I queued into my
2.6.28 update chain.


commit 42a7fa8d8a7f1680cba76e4824dba30bfd1c9d70
Author: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx>
Date: Wed Sep 10 20:19:40 2008 +0900

x86: avoid unnecessary low zone allocation in AMD IOMMU's alloc_coherent

x86's common alloc_coherent (dma_alloc_coherent in dma-mapping.h) sets
up the gfp flag according to the device dma_mask but AMD IOMMU doesn't
need it for devices that the IOMMU can do virtual mappings for. This
patch avoids unnecessary low zone allocation.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx>
Signed-off-by: Joerg Roedel <joerg.roedel@xxxxxxx>

diff --git a/arch/x86/kernel/amd_iommu.c b/arch/x86/kernel/amd_iommu.c
index ae38b24..09261dc 100644
--- a/arch/x86/kernel/amd_iommu.c
+++ b/arch/x86/kernel/amd_iommu.c
@@ -1360,6 +1360,9 @@ static void *alloc_coherent(struct device *dev, size_t size,
if (!check_device(dev))
return NULL;

+ if (!get_device_resources(dev, &iommu, &domain, &devid))
+ flag &= ~(__GFP_DMA | __GFP_HIGHMEM | __GFP_DMA32);
virt_addr = (void *)__get_free_pages(flag, get_order(size));
if (!virt_addr)
return 0;
@@ -1367,8 +1370,6 @@ static void *alloc_coherent(struct device *dev, size_t size,
memset(virt_addr, 0, size);
paddr = virt_to_phys(virt_addr);

- get_device_resources(dev, &iommu, &domain, &devid);
if (!iommu || !domain) {
*dma_addr = (dma_addr_t)paddr;
return virt_addr;

| AMD Saxony Limited Liability Company & Co. KG
Operating | Wilschdorfer Landstr. 101, 01109 Dresden, Germany
System | Register Court Dresden: HRA 4896
Research | General Partner authorized to represent:
Center | AMD Saxony LLC (Wilmington, Delaware, US)
| General Manager of AMD Saxony LLC: Dr. Hans-R. Deppe, Thomas McCoy

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at