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Date: Thu, 5 May 2016 17:09:07 +0200
From: Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [BUG] vfio device assignment regression with THP ref counting
 redesign
Message-ID: <20160505150907.GF28755@redhat.com>
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To: Alex Williamson <alex.williamson@redhat.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>, kirill.shutemov@linux.intel.com, linux-kernel@vger.kernel.org, "linux-mm@kvack.org" <linux-mm@kvack.org>

On Thu, May 05, 2016 at 04:39:24PM +0200, Andrea Arcangeli wrote:
> I'm currently testing this:

I must have been testing an earlier version, this below has better
chance not to oops. There's a reason I didn't attempt a proper submit
yet.. this is just for testing until we're sure this ok.

I also had a version of it initially that added a "*local_rmap"
instead of a *total_mapcount parameter to reuse_swap_page but then I
don't think gcc would have optimized things away enough depending on
the kernel config. reuse_swap_page couldn't just forward the
"total_mapcount" pointer from caller to callee anymore. So this
results in less code at the very least but then we've to check
"total_mapcount == 1" instead of just a true/false "local_rmap" (which
might have been more self explanatory) if reuse_swap_page returns
true.