On Fri, 2009-08-07 at 13:28 -0700, Russell King - ARM Linux wrote: > The kernel direct mapping maps all system (low) memory with normal > memory cacheable attributes. > > So using vmalloc, dma_alloc_coherent, using pages in userspace all > create duplicate mappings of pages. > If we do want to remove all these duplicate mappings, as part of solution to deal with the speculative prefetching, probably one way is to not map all the RAM into the direct-mapped space at paging_init() time, and instead map them on-demand by different upper layer allocation functions, such as vmalloc/dma_alloc_coherent/do_brk/kmalloc/ get_free_pages/etc. But then the distinction between upper layer allocation functions and non-upper layer ones must be made clear though. I know that mapping the RAM at paging_init() time can take advantage of 1M section mapping most of the time, and thus save many 1KB L2 page tables. But a lot of memory still ends up being remapped with L2 page tables later on, and meanwhile 1KB might not be as "precious" as it used to be as well-:) David -- 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
