forked from Minki/linux
0dd5b7b09e
If max_phys_bits needs to be > 43 (f.e. for T4 chips), things like DEBUG_PAGEALLOC stop working because the 3-level page tables only can cover up to 43 bits. Another problem is that when we increased MAX_PHYS_ADDRESS_BITS up to 47, several statically allocated tables became enormous. Compounding this is that we will need to support up to 49 bits of physical addressing for M7 chips. The two tables in question are sparc64_valid_addr_bitmap and kpte_linear_bitmap. The first holds a bitmap, with 1 bit for each 4MB chunk of physical memory, indicating whether that chunk actually exists in the machine and is valid. The second table is a set of 2-bit values which tell how large of a mapping (4MB, 256MB, 2GB, 16GB, respectively) we can use at each 256MB chunk of ram in the system. These tables are huge and take up an enormous amount of the BSS section of the sparc64 kernel image. Specifically, the sparc64_valid_addr_bitmap is 4MB, and the kpte_linear_bitmap is 128K. So let's solve the space wastage and the DEBUG_PAGEALLOC problem at the same time, by using the kernel page tables (as designed) to manage this information. We have to keep using large mappings when DEBUG_PAGEALLOC is disabled, and we do this by encoding huge PMDs and PUDs. On a T4-2 with 256GB of ram the kernel page table takes up 16K with DEBUG_PAGEALLOC disabled and 256MB with it enabled. Furthermore, this memory is dynamically allocated at run time rather than coded statically into the kernel image. Signed-off-by: David S. Miller <davem@davemloft.net> Acked-by: Bob Picco <bob.picco@oracle.com> |
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