On Fri, Sep 14, 2012 at 10:49:27AM +0200, javier Martin wrote: > Hello, > we use arm_memblock_steal() + dma_declare_coherent_memory() in order > to reserve son contiguous video memory in our platform: > http://git.linuxtv.org/media_tree.git/blob/refs/heads/staging/for_v3.7:/arch/arm/mach-imx/mach-imx27_visstrim_m10.c > > We've noticed that some restrictive alignment constraints are being > applied. For example, for coda driver, the following allocations are > made: > > coda coda-imx27.0: dma_alloc_from_coherent: try to allocate 557056 > bytes, out of 8388608 (vaddr = 0xc6000000) PAGE_SHIFT = 0xc > coda coda-imx27.0: dma_alloc_from_coherent: try to allocate 65536 > bytes, out of 8388608 (vaddr = 0xc6100000) PAGE_SHIFT = 0xc > coda coda-imx27.0: dma_alloc_from_coherent: try to allocate 10240 > bytes, out of 8388608 (vaddr = 0xc6110000) PAGE_SHIFT = 0xc > coda coda-imx27.0: dma_alloc_from_coherent: try to allocate 622080 > bytes, out of 8388608 (vaddr = 0xc6200000) PAGE_SHIFT = 0xc > coda coda-imx27.0: dma_alloc_from_coherent: try to allocate 622080 > bytes, out of 8388608 (vaddr = 0xc6300000) PAGE_SHIFT = 0xc > coda coda-imx27.0: dma_alloc_from_coherent: try to allocate 622080 > bytes, out of 8388608 (vaddr = 0xc6400000) PAGE_SHIFT = 0xc > coda coda-imx27.0: dma_alloc_from_coherent: try to allocate 589824 > bytes, out of 8388608 (vaddr = 0xc6500000) PAGE_SHIFT = 0xc > coda coda-imx27.0: dma_alloc_from_coherent: try to allocate 589824 > bytes, out of 8388608 (vaddr = 0xc6600000) PAGE_SHIFT = 0xc > coda coda-imx27.0: dma_alloc_from_coherent: try to allocate 622080 > bytes, out of 8388608 (vaddr = 0xc6700000) PAGE_SHIFT = 0xc > > If we take a look at the size of each allocation and the different > vaddr values we find that the alignment is 0x100000 = 1MB for values > like 622080 byte size. Why is that? Have you thought about get_order() on the allocation size, and what the resulting order will be? I'm sure if you could come up with a better allocation algorithm for this which doesn't lead to too much fragmentation (or convert it to use the pool infrastructure)... BTW, your question has nothing to do with arm_memblock_steal(). -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
