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Date: Wed, 01 Dec 2010 21:24:25 -0700
From: Warner Losh <imp@bsdimp.com>
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To: freebsd-mips@freebsd.org, Alan Cox <alc@cs.rice.edu>
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Subject: Re: vm_page_startup()
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On 11/30/2010 23:03, Alan Cox wrote:
> Given this bit of code in the MIPS pmap:
>
> vm_offset_t
> pmap_map(vm_offset_t *virt, vm_offset_t start, vm_offset_t end, int prot)
> {
>    vm_offset_t va, sva;
>
>    if (MIPS_DIRECT_MAPPABLE(end))
>        return (MIPS_PHYS_TO_DIRECT(start));
All mips architectures have at least a small direct map...

> The following in vm_page_startup() can apply to MIPS (as well as amd64):
>
> #ifdef __amd64__
>    /*
>     * pmap_map on amd64 comes out of the direct-map, not kvm like i386,
>     * so the pages must be tracked for a crashdump to include this data.
>     * This includes the vm_page_array and the early UMA bootstrap pages.
>     */
>    for (pa = new_end; pa < phys_avail[biggestone + 1]; pa += PAGE_SIZE)
>        dump_add_page(pa);
> #endif
>
> Even if a particular MIPS-based machine didn't wind up using the 
> direct map for the pmap_map calls in vm_page_startup() there would be 
> no harm in having called dump_add_page().  On the other hand, if you 
> don't call dump_add_page() when the direct map is used, you're crash 
> dump will be missing some kernel data structures.
So would you suggest having:

#if defined(__mips__) || defined(__amd64__)

or

#if __VM_HAS_DIRECT_MAP

and adding that define to pmap.h for mips and amd64?  I'm leaning to the 
latter, since I don't like #ifdef arch in vm/* code on general 
principles, but you're the maintainer...

Warner