what's zero_pages for in paging_int

[Ni@m]

Hello, rocky.
Mostly zeropage is needed to catch NULL-dereferencing.

Regards.
-- Dima

2009/10/30 胡杨树 <914059751 at qq.com>

> Hi, guys
>
>     In paging_int, after setting up bootmem allocator, why zero page is
> needed? i cannot see any things usefull resides on that page, something i
> missing obviously?
>
>    thanks
> ----rocky
>
>  ---------------------Linux-2.6.30/arch/arm/mm/mmu.c-----------------------
>
> void __init paging_init(struct machine_desc *mdesc)
> {
>         void *zero_page;
>
>         build_mem_type_table();
>         sanity_check_meminfo();
>         prepare_page_table();
>         bootmem_init();
>         devicemaps_init(mdesc);
>         kmap_init();/*DF: most embedded system do NOT have any HIGH MEM */
>         top_pmd = pmd_off_k(0xffff0000);
>
>
>         /*
>          * allocate the zero page.  Note that this always succeeds and
>          * returns a zeroed result.
>          */
>         zero_page = alloc_bootmem_low_pages(PAGE_SIZE);   /* DF: what’s
> this for? */
>         empty_zero_page = virt_to_page(zero_page);
>         flush_dcache_page(empty_zero_page);
>
> }
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