From mboxrd@z Thu Jan  1 00:00:00 1970
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Subject: Re: [RFC][PATCH v3 1/6] mm: Don't unmap gup()ed page
Date: Wed, 15 Apr 2009 20:39:04 +0900
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Cc: Nick Piggin <nickpiggin@yahoo.com.au>,
	LKML <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@osdl.org>,
	Andrew Morton <akpm@osdl.org>, Jeff Moyer <jmoyer@redhat.com>,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
	Hugh Dickins <hugh@veritas.com>
To: Andrea Arcangeli <aarcange@redhat.com>
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>> + =A0 =A0 if (!migration) {
>> + =A0 =A0 =A0 =A0 =A0 =A0 /* re-check */
>> + =A0 =A0 =A0 =A0 =A0 =A0 if (PageSwapCache(page) &&
>> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 page_count(page) !=3D page_mapcoun=
t(page) + 2) {
>> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 /* We lose race against ge=
t_user_pages_fast() */
>> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 set_pte_at(mm, address, pt=
e, pteval);
>> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ret =3D SWAP_FAIL;
>> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 goto out_unmap;
>> + =A0 =A0 =A0 =A0 =A0 =A0 }
>> + =A0 =A0 }
>> + =A0 =A0 mmu_notifier_invalidate_page(vma->vm_mm, address);
>
> With regard to mmu notifier, this is the opposite of the right
> ordering. One mmu_notifier_invalidate_page must run _before_ the firs=
t
> check. The ptep_clear_flush_notify will then stay and there's no need
> of a further mmu_notifier_invalidate_page after the second check.

OK. but I have one question.

Can we assume mmu_notifier is only used by kvm now?
if not, we need to make new notifier.
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