[PATCH -mm] mincore: apply page table walker on do_mincore() (Re: [PATCH 00/10] mm: pagewalk: huge page cleanups and VMA passing)

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

On Mon, Jun 02, 2014 at 02:53:34PM -0700, Dave Hansen wrote:
> On 06/02/2014 02:52 PM, Naoya Horiguchi wrote:
> > What version is this patchset based on?
> > Recently I comprehensively rewrote page table walker (from the same motivation
> > as yours) and the patchset is now in linux-mm. I guess most of your patchset
> > (I've not read them yet) conflict with this patchset.
> > So could you take a look on it?
> 
> It's on top of a version of Linus's from the last week.  I'll take a
> look at how it sits on top of -mm.

I've looked over your series, but unfortunately most of works (patch 1, 2, 3,
5, 6, 7) were already done or we don't have to do it in current linux-mm code.
Problems you try to handle in these patches come from current code's poor
design of page table walker, worst thing is that we do vma-loop inside pgd loop.
I know you tried harder to make things better, but I don't think it make sense
to maintain current bad base code for long.

As for patch 4, yes, we can apply page table walker do_mincore() and I have
a patch applicable onto linux-mm code (attached). And for other potential
page walk users, I'm investigating whether we can really apply page table
walker (some caller doesn't hold mmap_sem, so can't simply apply it.)

And for patch 8, 9, and 10, I don't think it's good idea to add a new callback
which can handle both pmd and pte (because they are essentially differnt thing).
But the underneath idea of doing pmd_trans_huge_lock() in the common code in
walk_single_entry_locked() looks nice to me. So it would be great if we can do
the same thing in walk_pmd_range() (of linux-mm) to reduce code in callbacks.

Thanks,
Naoya Horiguchi
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