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Date: Tue, 8 Jan 2013 19:03:46 +0100
From: Andrea Arcangeli <aarcange@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
        Hillf Danton <dhillf@gmail.com>, Hugh Dickins <hughd@google.com>,
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        Linux Kernel <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>, Linux-MM <linux-mm@kvack.org>,
        Rik van Riel <riel@redhat.com>
Subject: Re: oops in copy_page_rep()
Message-ID: <20130108180346.GH9163@redhat.com>
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On Tue, Jan 08, 2013 at 09:51:47AM -0800, Linus Torvalds wrote:
> On Tue, Jan 8, 2013 at 9:37 AM, Andrea Arcangeli <aarcange@redhat.com> wrote:
> >
> > The reason it returned to userland and retried the fault is that this
> > should be infrequent enough not to worry about it and this was
> > marginally simpler but it could be changed.
> 
> Yeah, that was my suspicion. And as mentioned, returning to user land
> might actually help with scheduling and/or signal handling latencies
> etc, so it might be the right thing to do.  Especially if the
> alternative is to just busy-loop.
> 
> > If we don't want to return to userland we should wait on the splitting
> > bit and then take the pte walking routines like if the pmd wasn't
> > huge. This is not related to the below though.
> 
> How does this patch sound to people? It does the splitting check
> before the access bit set (even though I don't think it matters), and
> at least talks about the alternatives and the issues a bit.
> 
> Hmm?

It looks very fine to me, but I suggest to move it above the
pmd_numa() check because of the newly introduced
migrate_misplaced_transhuge_page method relying on pmd_same too.

Thanks!