Re: [uml-devel] duplicated mem_map (struct page) array?

[Richard W. <ric...@gm...>]

On Fri, May 30, 2014 at 10:24 AM, enjoy mindful <enj...@gm...> wrote:
> Hi,
>  When I'm trace uml kernel with gdb, I found there are two mem_map
> (struct page) arrays.
>
> 1) the first one created in init_maps function, and pointed by *local*
> pointer struct page *map in init_maps function
>
> arch/um/kernel/um_arch.c
> 264 int __init linux_main(int argc, char **argv)
> .....
> 350         setup_physmem(uml_physmem, uml_reserved, physmem_size, highmem);
> 351         if (init_maps(physmem_size, iomem_size, highmem)) {
> 352                 printf("Failed to allocate mem_map for %Lu bytes
> of physical "
> 353                        "memory and %Lu bytes of highmem\n", physmem_size,
> 354                        highmem);
> 355                 exit(1);
> 356         }
>
> 2) the second mem_map created in
> start_kernel -> setup_arch -> paging_init -> free_area_init ->
> free_area_init_core -> alloc_node_mem_map
>
> and it has been pointer by global pointer "contig_page_data->node_mem_map"
>
> Why need struct page array (the first one) for boot memory allocate? I
> tried to deleted the 351~356 lines in linux_main function and the
> built/run the uml kernel. The new kernel can boot and run. But it may
> panic.

Linux has only one mem_map array, defined in mm/memory.
I also fail to see how the kernel can work if you delete the call to
init_maps().

*confused* :)

-- 
Thanks,
//richard