Messages in this thread | | | Date | Thu, 2 Jul 2015 00:34:30 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH 05/11] mm: debug: dump page into a string rather than directly on screen |
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On Wed, Jul 01, 2015 at 02:25:56PM -0700, David Rientjes wrote: > 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);
Huh? How would we reach this, if VM_BUG_ON() will trigger BUG()?
> } > > 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.
-- Kirill A. Shutemov
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