[Linaro-mm-sig] [RFC 2/4] ARM: dma-mapping: IOMMU allocates pages from pool with GFP_ATOMIC

Hi.

We have faced with WQXGA(2560x1600) support and framebuffers become dramatically larger. Moreover, high resolution camera sensors also press memory use more than the screen size.

However, I think that it is enough with your change because allocation failure of several contiguous pages also shows that the system don't have enough memory.

On Wed, Aug 22, 2012 at 10:36 PM, Hiroshi Doyu hdoyu@nvidia.com wrote:

Hi,

KyongHo Cho pullip.cho@samsung.com wrote @ Wed, 22 Aug 2012 14:47:00

+0200:

...

vzalloc() call in __iommu_alloc_buffer() also causes BUG() in atomic

context.

Right.

I've been thinking that kzalloc() may be enough here, since vzalloc() was introduced to avoid allocation failure for big chunk of memory, but I think that it's unlikely that the number of page array can be so big. So I propose to drop vzalloc() here, and just simply to use kzalloc only as below(*1).

For example,

1920(H) x 1080(W) x 4(bytes) ~= 8MiB

For 8 MiB buffer, 8(MiB) * 1024 = 8192(KiB) 8192(KiB) / 4(KiB/page) = 2048 pages sizeof(struct page *) = 4 bytes 2048(pages) * 4(bytes/page) = 8192(bytes) = 8(KiB) 8(KiB) / 4(KiB/page) = 2 pages

If the above estimation is right(I hope;)), the necessary pages are _at most_ 2 pages. If the system gets into the situation to fail to allocate 2 contiguous pages, that's real the problem. I guess that that kind of fragmentation problem would be solved with page migration or something, especially nowadays devices are getting larger memories.

*1: From a613c40d1b3d4fb1577cdb0807a74e8dbd08a3e6 Mon Sep 17 00:00:00 2001 From: Hiroshi Doyu hdoyu@nvidia.com Date: Wed, 22 Aug 2012 16:25:54 +0300 Subject: [PATCH 1/1] ARM: dma-mapping: Use only kzalloc without vzalloc

Use only kzalloc for atomic allocation.

Signed-off-by: Hiroshi Doyu hdoyu@nvidia.com

arch/arm/mm/dma-mapping.c | 10 ++-------- 1 files changed, 2 insertions(+), 8 deletions(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c index 4656c0f..d4f1cf2 100644 --- a/arch/arm/mm/dma-mapping.c +++ b/arch/arm/mm/dma-mapping.c @@ -1083,10 +1083,7 @@ static struct page **__iommu_alloc_buffer(struct

device *dev, size_t size,

    int count = size >> PAGE_SHIFT;
    int array_size = count * sizeof(struct page *);

•   if (array_size <= PAGE_SIZE)
  

•           pages = kzalloc(array_size, gfp);
  

•   else
  

•           pages = vzalloc(array_size);
  

•   pages = kzalloc(array_size, gfp);
    if (!pages)
            return NULL;
  
  

@@ -1107,10 +1104,7 @@ static struct page **__iommu_alloc_buffer(struct

device *dev, size_t size,

    return pages;

error:

•   if (array_size <= PAGE_SIZE)
  

•           kfree(pages);
  

•   else
  

•           vfree(pages);
  

•   kfree(pages);
    return NULL;
  

}

-- 1.7.5.4

-- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a hrefmailto:"dont@kvack.org"> email@kvack.org </a>