Hi all, while looking into DMA allocation, I noticed that __dma_direct_optimal_gfp_mask() in kernel/dma/direct.c can probably be improved. It uses GFP_DMA if dev->coherent_dma_mask is less than DMA_BIT_MASK(ARCH_ZONE_DMA_BITS). There is no s390-specific definition of ARCH_ZONE_DMA_BITS. The default is 24 bits, but the DMA zone on s390 is 31 bits. CCW subchannel devices set sch->dev.coherent_dma_mask to DMA_BIT_MASK(31), which is greater than DMA_BIT_MASK(24), so buffers are allocated from the Normal zone first. Would it make sense to set ARCH_ZONE_BITS to 31 on s390, or did I miss something? Petr T
