Hi,
KyongHo Cho <pullip....@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 <hd...@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 <hd...@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
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