On Wed, 1 Jul 2015, Sasha Levin wrote:
> 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.
>
I think it's a debate about whether this would be better off handled as
if (VM_BUG_ON(compound_head(page) != head)) {
dump_page(page);
dump_page(head);
}
and avoid VM_BUG_ON_PAGE() and the new print formats entirely. We can
improve upon existing VM_BUG_ON(), and BUG_ON() itself since the VM isn't
anything special in this regard, to print diagnostic information that may
be helpful, but I don't feel like adding special VM_BUG_ON_*() macros or
printing formats makes any of this simpler.
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