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> 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? > 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. > 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. |
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