Hi, KyongHo Cho <pullip.cho@xxxxxxxxxxx> 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@xxxxxxxxxx> 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@xxxxxxxxxx> --- 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@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href