From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f180.google.com (mail-wi0-f180.google.com [209.85.212.180]) by kanga.kvack.org (Postfix) with ESMTP id 578A16B0038 for ; Wed, 17 Sep 2014 13:21:42 -0400 (EDT) Received: by mail-wi0-f180.google.com with SMTP id ex7so1666411wid.1 for ; Wed, 17 Sep 2014 10:21:41 -0700 (PDT) Received: from mail-wi0-f178.google.com (mail-wi0-f178.google.com [209.85.212.178]) by mx.google.com with ESMTPS id lc8si29146404wjb.43.2014.09.17.10.21.40 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 17 Sep 2014 10:21:40 -0700 (PDT) Received: by mail-wi0-f178.google.com with SMTP id ho1so1659010wib.5 for ; Wed, 17 Sep 2014 10:21:40 -0700 (PDT) Date: Wed, 17 Sep 2014 20:21:37 +0300 From: Gleb Natapov Subject: Re: [PATCH] kvm: Faults which trigger IO release the mmap_sem Message-ID: <20140917172137.GH26540@minantech.com> References: <1410811885-17267-1-git-send-email-andreslc@google.com> <20140917102635.GA30733@minantech.com> <20140917112713.GB1273@potion.brq.redhat.com> <20140917114214.GB30733@minantech.com> <20140917170841.GG26540@minantech.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Andres Lagar-Cavilla Cc: Radim =?utf-8?B?S3LEjW3DocWZ?= , Rik van Riel , Peter Zijlstra , Mel Gorman , Andy Lutomirski , Andrew Morton , Andrea Arcangeli , Sasha Levin , Jianyu Zhan , Paul Cassella , Hugh Dickins , Peter Feiner , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org On Wed, Sep 17, 2014 at 10:13:45AM -0700, Andres Lagar-Cavilla wrote: > On Wed, Sep 17, 2014 at 10:08 AM, Gleb Natapov wrote: > > On Wed, Sep 17, 2014 at 10:00:32AM -0700, Andres Lagar-Cavilla wrote: > >> On Wed, Sep 17, 2014 at 4:42 AM, Gleb Natapov wrote: > >> > 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. > >> >> > >> >> 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 f= ault. > >> > >> The point is that the gup in the async pf completion from the work > >> queue will not relinquish the mmap semaphore. And it most definitely > >> should, given that we are likely looking at swap/filemap. > >> > > I get this point and the patch looks good in general, but my point is > > that when _retry() is called from async_pf_execute() second gup is not > > needed. In the original code gup is called to do IO and nothing else. > > In your patch this is accomplished by the first gup already, so you > > can skip second gup if pagep =3D=3D nullptr. >=20 > I see. However, if this function were to be used elsewhere in the > future, then the "if pagep =3D=3D NULL don't retry" semantics may not > match the new caller's intention. Would you prefer an explicit flag? >=20 We can add explicit flag whenever such caller will be added, if ever. -- Gleb. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org