Re: oops in copy_page_rep()

[Linus Torvalds <torvalds@linux-foundation.org>]

On Tue, Jan 8, 2013 at 8:31 AM, Kirill A. Shutemov <kirill@shutemov.name> wrote:
>>
>> Heh. I was more thinking about why do_huge_pmd_wp_page() needs it, but
>> do_huge_pmd_numa_page() does not.
>
> It does. The check should be moved up.
>
>> Also, do we actually need it for huge_pmd_set_accessed()? The
>> *placement* of that thing confuses me. And because it confuses me, I'd
>> like to understand it.
>
> We need it for huge_pmd_set_accessed() too.
>
> Looks like a mis-merge. The original patch for huge_pmd_set_accessed() was
> correct: http://lkml.org/lkml/2012/10/25/402

Not a merge error: the pmd_trans_splitting() check was removed by
commit d10e63f29488 ("mm: numa: Create basic numa page hinting
infrastructure").

Now, *why* it was removed, I can't tell. And it's not clear why the
original code just had it in a conditional, while the suggested patch
has that "goto repeat" thing. I suspect re-trying the fault (which I
assume the original code did) is actually better, because that way you
go through all the "should I reschedule as I return through the
exception" stuff. I dunno.

Mel, that original patch came from you , although it was based on
previous work by Peter/Ingo/Andrea. Can you walk us through the
history and thinking about the loss of pmd_trans_splitting(). Was it
purely a mistake? It looks intentional.

               Linus

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