Hi, On Mon, Jun 25, 2012 at 9:01 PM, 卜弋天 <buyit@xxxxxxx> wrote: > >> Suppose your machine has 1 GB of RAM with a physical addresses of >> 0x40000000 thru 0x7FFFFFFF >> >> Let's suppose that PHYS_OFFSET = 0xC0000000 >> Let's suppose that VMALLOC_START is set to 0xE0000000 and VMALLOC_END >> is at 0xEFFFFFFF (256 Mb) >> > is this PAGE_OFFSET or PHYS_OFFSET? PAGE_OFFSET is a virtual address, and PHYS_OFFSET is a physical address, so you are correct. That should have been PAGE_OFFSET. >> So what we have is that memory from 0xC0000000 thru 0xDFFFFFFF (512 >> Mb) is kernel direct mapped memory and maps to physical addresses >> 0x40000000 thru 0x5FFFFFFF >> >> Physical memory from 0x60000000 thru 0x7FFFFFFF (512Mb) is considered >> high-mem. For the most part this is only usable by user-space. From >> kernel space, you need to use the kmap/kunmap functions to even access >> the memory. >> > i don't think high-memory is only used by user-space. > vmalloc() funciton will try to allocate physical memory from high_memory > first, if there is no high_memory, then allocate from normal region. That also seems to be correct. The code in vmalloc that calls the underlying page allocator passes in __GFP_HIGHMEM, so it will try to use highmem for vmalloc'd pages. >> However, if you call vmalloc and lets suppose that vmalloc just >> happens to return 0xE0000000. The physical address of the first page >> might be 0xD2345000. >> > suppose vmalloc() return 0xE0000000, which is the VMALLOC_START, then the > physical memory address > should be 0x60000000 thru 0x7FFFFFFF in your example. > > >> What's important is that the physical pages which back up the vmalloc >> area all come from the kernel direct mapped area. They won't ever be >> backed by pages from high-memory. So the physical addresses will all >> be in the range 0x40000000 thru 0x5FFFFFFF. >> > what do you mean "back up", maybe i have some misunderstanding. > in my opnion, vmalloc area should map to physical address 0x60000000 thru > 0x7FFFFFFF first, > if this resion is exhausted, then normal area will be allocated. By backed-by, I meant the associated physical page. I was incorrect in saying that only lowmem pages would be used. -- Dave Hylands Shuswap, BC, Canada http://www.davehylands.com _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
