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Date: Wed, 17 Sep 2014 14:42:15 +0300
From: Gleb Natapov <gleb@kernel.org>
Subject: Re: [PATCH] kvm: Faults which trigger IO release the mmap_sem
Message-ID: <20140917114214.GB30733@minantech.com>
References: <1410811885-17267-1-git-send-email-andreslc@google.com>
 <20140917102635.GA30733@minantech.com>
 <20140917112713.GB1273@potion.brq.redhat.com>
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To: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
Cc: Andres Lagar-Cavilla <andreslc@google.com>, Gleb Natapov <gleb@redhat.com>, Rik van Riel <riel@redhat.com>, Peter Zijlstra <peterz@infradead.org>, Mel Gorman <mgorman@suse.de>, Andy Lutomirski <luto@amacapital.net>, Andrew Morton <akpm@linux-foundation.org>, Andrea Arcangeli <aarcange@redhat.com>, Sasha Levin <sasha.levin@oracle.com>, Jianyu Zhan <nasa4836@gmail.com>, Paul Cassella <cassella@cray.com>, Hugh Dickins <hughd@google.com>, Peter Feiner <pfeiner@google.com>, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org

On Wed, Sep 17, 2014 at 01:27:14PM +0200, Radim Kr=C4=8Dm=C3=A1=C5=99 wrote:
> 2014-09-17 13:26+0300, Gleb Natapov:
> > For async_pf_execute() you do not need to even retry. Next guest's page=
 fault
> > will retry it for you.
>=20
> Wouldn't that be a waste of vmentries?
This is how it will work with or without this second gup. Page is not
mapped into a shadow page table on this path, it happens on a next fault.

--
			Gleb.

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