On Thu, Jul 18, 2019 at 09:17:00AM +0200, Petr Tesarik wrote: > 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? No, this seems to be broken. Halil, can you look into this and provide a patch?
