Cyrill Gorcunov

Email: MailTo(gorcunov AT SPAMFREE gmail DOT com)

Interesting links

• Virtual Memory: Issues Of Implementation http://www.eng.umd.edu/~blj/papers/computer31-6.pdf

• Memory Subsystem (lecture) http://www.ece.gatech.edu/academic/courses/summer2007/ece3055/Lectures/VirtualMemory/VirtualMemory-lee.pdf

My notes on Linux kernel internals

x86-32 memory initialization

Paging is initialized in arch/x86/mm/init_32.c. The function 'paging_init()' is called once by setup_arch during kernel initialization. It immediately calls pagetable_init(). pagetable_init() starts by defining the base of the page table directory:

*pgd_base = swapper_pg_dir;

swapper_pg_dir is defined in head_32.S as

.section ".bss.page_aligned","wa"
        .align PAGE_SIZE_asm
ENTRY(swapper_pg_dir)
        .fill 1024,4,0

that creates an array of 1024 entries each of 4 bytes length (Page Directory entries in terms of Intel manual). A such definition allows ld program to place swapper_pg_dir at special predefined memory address while linking a kernel. It points to 0x1000 above the 'root' of kernel memory. Kernel memory is defined to start at PAGE_OFFSET, which is 0XC0000000 for x86, or 3 gigabytes. (This is where the 3G/1G split is defined.) Every virtual address above PAGE_OFFSET is the kernel, any address below PAGE_OFFSET is a user space. Further is available on http://linux-mm.org/VirtualMemory

x86-32 memory initialization (SMP)

To be continued...

TODO

POWERPC

 + add for_each_child_node() macro
 - convert all cycles for(...) to for_each_child_node()
 ~ convert all for(...) to for_each_compatible_node()
 - check for NULL dereference on of_find_property()
 - check for of_node_put() call after node has been used
Legend:
 (+) - done
 (~) - in progress
 (-) - have to

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