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; }