On Wed, Apr 16, 2014 at 11:33 AM, Laura Abbott <lauraa@xxxxxxxxxxxxxx> wrote: > On 4/16/2014 11:11 AM, Lin Ming wrote: >> Hi Peter, >> >> I have a performance problem(on ARM board) that cpu is very bus at >> cache invalidation. >> So I'm trying to alloc an uncached memory to eliminate cache invalidation. >> >> But I also have problem with dma_alloc_coherent(). >> If I don't use dma_alloc_coherent(), is it OK to use below code to >> alloc uncached memory? >> >> struct page *page; >> pgd_t *pgd; >> pud_t *pud; >> pmd_t *pmd; >> pte_t *pte; >> void *cpu_addr; >> dma_addr_t dma_addr; >> unsigned int vaddr; >> >> cpu_addr = kmalloc(PAGE_SIZE, GFP_KERNEL); >> dma_addr = pci_map_single(NULL, cpu_addr, PAGE_SIZE, (int)DMA_FROM_DEVICE); >> vaddr = (unsigned int)uncached->cpu_addr; >> pgd = pgd_offset_k(vaddr); >> pud = pud_offset(pgd, vaddr); >> pmd = pmd_offset(pud, vaddr); >> pte = pte_offset_kernel(pmd, vaddr); >> page = virt_to_page(vaddr); >> set_pte_ext(pte, mk_pte(page, pgprot_dmacoherent(pgprot_kernel)), 0); >> >> /* This kmalloc memory won't be freed */ >> > > No, that will not work. lowmem pages are mapped with 1MB sections underneath > which cannot be (easily) changed at runtime. You really want to be using > dma_alloc_coherent here. For "lowmem pages", do you mean the first 16M physical memory? How about that if I only use highmem pages(>16M)? Thanks. > > Laura > > -- > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, > hosted by The Linux Foundation -- 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=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>