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    SubjectRe: [PATCH] swiotlb: fix dma_alloc_coherent allocation failures with swiotlb
    On Thu, Sep 04, 2008 at 03:05:21AM +0900, FUJITA Tomonori wrote:
    > On Wed, 3 Sep 2008 17:03:44 +0200
    > Joerg Roedel <joerg.roedel@amd.com> wrote:
    >
    > > The SWIOTLB version of dma_alloc_coherent allocates all memory with
    > > GFP_DMA unconditionally. This leads sometimes unnecessary to allocation
    > > failures. This patch makes the allocation strategy to use the DMA32 zone
    > > first if this is possible. The changes are boot tested on AMD64 and
    > > compile tested for i386 and IA64.
    > >
    > > Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > > Cc: tony.luck@intel.com
    > > Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
    > > ---
    > > lib/swiotlb.c | 23 +++++++++++++++++------
    > > 1 files changed, 17 insertions(+), 6 deletions(-)
    >
    > This doesn't look correct since IA64 doesn't need this flag hack.

    Thats why the patch checks the DMA mask against ISA_DMA_THRESHOLD. This
    is defined as the border of the ZONE_DMA (16MB on x86 and 4G on IA64).
    So is correct for x86 and ia64.

    > Another problem about this patch is that swiotlb doesn't use GFP_DMA
    > for the fallback_dev.

    Thats not true, it does. ISA_DMA_THRESHOLD is defined to be the same as
    DMA_24BIT_MASK, which is the DMA mask of the fallback_dev.

    Joerg



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