[PATCH] x86: avoid unnecessary low zone allocation in AMD IOMMU'salloc_coherent

From: FUJITA Tomonori
Date: Wed Sep 10 2008 - 07:20:24 EST

This is for tip/iommu.

btw, Joery, what happens if map_sg (or map_single) gets
not-DMA-capable buffer in the case of !iommu || !domain?

From: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx>
Subject: [PATCH] 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>
arch/x86/kernel/amd_iommu.c | 7 +++++--
1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/amd_iommu.c b/arch/x86/kernel/amd_iommu.c
index 01c68c3..8efd249 100644
--- a/arch/x86/kernel/amd_iommu.c
+++ b/arch/x86/kernel/amd_iommu.c
@@ -999,6 +999,11 @@ static void *alloc_coherent(struct device *dev, size_t size,
u16 devid;
phys_addr_t paddr;

+ get_device_resources(dev, &iommu, &domain, &devid);
+ if (iommu && domain)
+ flag &= ~(__GFP_DMA | __GFP_HIGHMEM | __GFP_DMA32);
virt_addr = (void *)__get_free_pages(flag, get_order(size));
if (!virt_addr)
return 0;
@@ -1006,8 +1011,6 @@ 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;

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