Hi,
I was going through the Memory Initialization document at www.linux-mm.org/
I am trying to understand the bootmem allocator.Nothing much is written about those functions
except for a few lines.
I believe the virtual memory above PAGE_OFFSET is reserved for kernel.
Here is my analysis of the setup_arch() from kernel/setup.c.Please correct me if I am wrong.
1. /*
* Partially used pages are not usable - thus
* we are rounding upwards.
*/
start_pfn = PFN_UP(__pa(&_end));
This is the page frame number in the physical memory above which the bootmem would be allocated.
2. The next part of the code is a for loop that calculates the highest page frame number which would
be nothing but the end of physical memory.
3. Then there is a call to init_bootmem.
4. In the init_bootmem routine, I would like to know what is the "mapsize" for.What does it indicate?
5. In the same routine, a bootmem structure is filled with values for the virtual address of start_pfn,
the start address and an entry for the highest page frame number.Then the memory starting at
bootmem_map is initialized.
6.Returning to setup_arch(),.there is a for loop that does not do a lot.
7.Then there is a call to reserve_bootmem() with the physical address of the first usable page frame
as one of its arguments.
8. In the reserve_bootmem routine, what do sidx,eidx and end point to? I am not sure if sidx and eidx
point to the physical page numbers needed for bootmem.
I could be wrong at a few places.
Thanks,
Manoj
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