On 01/30/2013 04:56 PM, Dave Hansen wrote:
> This code was an optimization for 32-bit NUMA systems.
>
> It has probably been the cause of a number of subtle bugs over
> the years, although the conditions to excite them would have
> been hard to trigger. Essentially, we remap part of the kernel
> linear mapping area, and then sometimes part of that area gets
> freed back in to the bootmem allocator. If those pages get
> used by kernel data structures (say mem_map[] or a dentry),
> there's no big deal. But, if anyone ever tried to use the
> linear mapping for these pages _and_ cared about their physical
> address, bad things happen.
>
> For instance, say you passed __GFP_ZERO to the page allocator
> and then happened to get handed one of these pages, it zero the
> remapped page, but it would make a pte to the _old_ page.
> There are probably a hundred other ways that it could screw
> with things.
>
> We don't need to hang on to performance optimizations for
> these old boxes any more. All my 32-bit NUMA systems are long
> dead and buried, and I probably had access to more than most
> people.
>
> This code is causing real things to break today:
>
> https://lkml.org/lkml/2013/1/9/376
>
> I looked in to actually fixing this, but it requires surgery
> to way too much brittle code, as well as stuff like
> per_cpu_ptr_to_phys().
>
I get a build failure on i386 allyesconfig with this patch:
arch/x86/power/built-in.o: In function `swsusp_arch_resume':
(.text+0x14e4): undefined reference to `resume_map_numa_kva'
It looks trivial to fix up; I assume resume_map_numa_kva() just goes
away like it does in the non-NUMA case, but it would be nice if you
could confirm that.
-hpa
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