[PATCH] ARM: dma: Drop __GFP_COMP for iommu dma memory allocations

[Hiroshi Doyu]

Richard Zhao <linuxzsc at gmail.com> wrote @ Thu, 20 Jun 2013 15:40:50 +0200:

> >> +       /*
> >> +        * Following is a work-around (a.k.a. hack) to prevent pages
> >> +        * with __GFP_COMP being passed to split_page() which cannot
> >> +        * handle them.  The real problem is that this flag probably
> >> +        * should be 0 on ARM as it is not supported on this
> >> +        * platform; see CONFIG_HUGETLBFS.
> >> +        */
> >> +       gfp &= ~(__GFP_COMP);
> >
> >
> >    Hm, what exactly is the sense you meant in using ()?
> 
> It's copy/paste from elsewhere in this file. At least it's consistent? :)

I almost sent the exact same one, actually it was under internal reivew;)

This patch is similar but is the iommu version of:


commit ea2e7057c0234cfb8b09467d8f137760d371fc72
Author: Sumit Bhattacharya <sumitb at nvidia.com>
Date:   Thu Nov 24 00:47:12 2011 +0100

    ARM: 7172/1: dma: Drop GFP_COMP for DMA memory allocations
    
    dma_alloc_coherent wants to split pages after allocation in order to
    reduce the memory footprint. This does not work well with GFP_COMP
    pages, so drop this flag before allocation.
    
    This patch is ported from arch/avr32
    (commit 3611553ef985ef7c5863c8a94641738addd04cff).
    
    [swarren: s/HUGETLB_PAGE/HUGETLBFS/ in comment, minor comment cleanup]
    
    Signed-off-by: Sumit Bhattacharya <sumitb at nvidia.com>
    Tested-by: Varun Colbert <vcolbert at nvidia.com>
    Signed-off-by: Stephen Warren <swarren at nvidia.com>
    Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index ab58456..1aa664a 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -332,6 +332,15 @@ __dma_alloc(struct device *dev, size_t size, dma_addr_t *handle, gfp_t gfp,
        struct page *page;
        void *addr;
 
+       /*
+        * Following is a work-around (a.k.a. hack) to prevent pages
+        * with __GFP_COMP being passed to split_page() which cannot
+        * handle them.  The real problem is that this flag probably
+        * should be 0 on ARM as it is not supported on this
+        * platform; see CONFIG_HUGETLBFS.
+        */
+       gfp &= ~(__GFP_COMP);
+
        *handle = ~0;
        size = PAGE_ALIGN(size);