James, Appreciate for your answer. One more question: do you think there are any compatibility issues on kmalloc/kfree pair? I just trace the kernel code. It looks like it would not. But I am not quite sure absolutely. May I have your comments? Thank you, -----Original Message----- From: James Bottomley [mailto:James.Bottomley@xxxxxxxxxxxxxxxxxxxxx] Sent: Monday, February 25, 2008 10:39 PM To: nick.cheng@xxxxxxxxxxxx Cc: 'Daniel Drake'; linux-scsi@xxxxxxxxxxxxxxx; 'erich' Subject: RE: Patch added to scsi-rc-fixes-2.6: [SCSI] arcmsr: fix messageallocation On Mon, 2008-02-25 at 18:47 +0800, nickcheng wrote: > Sorry, maybe I did not ask distinctly enough. > I mean if I would like to allocate a memory space from ZONE_DMA for atomic > context, why can I not use kmalloc(1032, GFP_ATOMIC|GFP_DMA)? > In case of lack of GFP_DMA, kmalloc would grab the memory from ZONE_HIGH or > ZONE_HIGHMEM, isn't it?(I read it from the textbook of Linux Kernel > Development by Robert Love) Um, no that's not true at all. GFP_DMA only allocates memory from ZONE_DMA and fails otherwise. You only need memory from ZONE_DMA if you cannot address physical memory above 24 bits (the old ISA restriction). This only applies if you're a standard ISA device and you're going actually to DMA to the memory in question. Neither of which applies in the arcmsr case, since you're only using the memory as a copy buffer within the kernel (it never sees an actual DMA transfer), and arcmsr doesn't have the ISA restrictions. > Or the basic is that you don't think it is necessary to allocate a memory > space from DMA area? > Please give me some comments. It's unnecessary because you never DMA to it, but even if you did, since arcmsr is a non-ISA device (with 64 bit DMA mask falling back to 32) you can just use ordinary kmalloc'd memory for that (provided you obey the coherence requirements). James - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
