On 06/30/2015 07:35 PM, David Rientjes wrote:
> I don't know how others feel, but this looks strange to me and seems like
> it's only a result of how we must now dump page information
> (dump_page(page) is no longer available, we must do pr_alert("%pZp",
> page)).
>
> Since we're relying on print formats, this would arguably be better as
>
> pr_alert("Not movable balloon page:\n");
> pr_alert("%pZp", page);
>
> to avoid introducing newlines into potentially lengthy messages that need
> a specified loglevel like you've done above.
>
> But that's not much different than the existing dump_page()
> implementation.
>
> So for this to be worth it, it seems like we'd need a compelling usecase
> for something like pr_alert("%pZp %pZv", page, vma) and I'm not sure we're
> ever actually going to see that. I would argue that
>
> dump_page(page);
> dump_vma(vma);
>
> would be simpler in such circumstances.
I think we can find usecases where we want to dump more information than what's
contained in just one page/vma/mm struct. Things like the following from mm/gup.c:
VM_BUG_ON_PAGE(compound_head(page) != head, page);
Where seeing 'head' would be interesting as well.
Or for VMAs, from include/linux/rmap.h:
VM_BUG_ON_VMA(vma->anon_vma != next->anon_vma, vma);
Would it be interesting to see both vma, and next? Probably.
Or opportunities to add information from other variables, such as in:
VM_BUG_ON_PAGE(stable_node->kpfn != page_to_pfn(oldpage), oldpage);
Is stable_node->kpfn interesting? Might be.
We *could* go ahead and open code all of that, but that's not happening, It's not
intuitive and people just slap VM_BUG_ON()s and hope they can figure it out when
those VM_BUG_ON()s happen.
Are there any pieces of code that open code what you suggested?
Thanks,
Sasha
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