linux-kernel - Re: [RFC][PATCH v3 1/6] mm: Don't unmap gup()ed page

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Message-ID: <2f11576a0904150439k6e828307ja97b6729650bcb94@mail.gmail.com>
Date:	Wed, 15 Apr 2009 20:39:04 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...l.org>,
	Andrew Morton <akpm@...l.org>, Jeff Moyer <jmoyer@...hat.com>,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	Hugh Dickins <hugh@...itas.com>
Subject: Re: [RFC][PATCH v3 1/6] mm: Don't unmap gup()ed page

>> +     if (!migration) {
>> +             /* re-check */
>> +             if (PageSwapCache(page) &&
>> +                 page_count(page) != page_mapcount(page) + 2) {
>> +                     /* We lose race against get_user_pages_fast() */
>> +                     set_pte_at(mm, address, pte, pteval);
>> +                     ret = SWAP_FAIL;
>> +                     goto out_unmap;
>> +             }
>> +     }
>> +     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 first
> 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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