From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk1-f198.google.com (mail-qk1-f198.google.com [209.85.222.198]) by kanga.kvack.org (Postfix) with ESMTP id 257F88E0001 for ; Mon, 21 Jan 2019 06:10:52 -0500 (EST) Received: by mail-qk1-f198.google.com with SMTP id z68so18971617qkb.14 for ; Mon, 21 Jan 2019 03:10:52 -0800 (PST) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id v21si11897840qth.252.2019.01.21.03.10.51 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 21 Jan 2019 03:10:51 -0800 (PST) Received: from pps.filterd (m0098421.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x0LB0h0L140117 for ; Mon, 21 Jan 2019 06:10:50 -0500 Received: from e06smtp05.uk.ibm.com (e06smtp05.uk.ibm.com [195.75.94.101]) by mx0a-001b2d01.pphosted.com with ESMTP id 2q5bdmc2v7-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Mon, 21 Jan 2019 06:10:50 -0500 Received: from localhost by e06smtp05.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 21 Jan 2019 11:10:48 -0000 Date: Mon, 21 Jan 2019 13:10:39 +0200 From: Mike Rapoport Subject: Re: [PATCH RFC 20/24] userfaultfd: wp: don't wake up when doing write protect References: <20190121075722.7945-1-peterx@redhat.com> <20190121075722.7945-21-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190121075722.7945-21-peterx@redhat.com> Message-Id: <20190121111039.GB26461@rapoport-lnx> Sender: owner-linux-mm@kvack.org List-ID: To: Peter Xu Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , Maya Gokhale , Jerome Glisse , Johannes Weiner , Martin Cracauer , Denis Plotnikov , Shaohua Li , Andrea Arcangeli , Pavel Emelyanov , Mike Kravetz , Marty McFadden , Mike Rapoport , Mel Gorman , "Kirill A . Shutemov" , "Dr . David Alan Gilbert" On Mon, Jan 21, 2019 at 03:57:18PM +0800, Peter Xu wrote: > It does not make sense to try to wake up any waiting thread when we're > write-protecting a memory region. Only wake up when resolving a write > protected page fault. Probably it would be better to make it default to wake up only when requested explicitly? Then we can simply disallow _DONTWAKE for uffd_wp and only use UFFDIO_WRITEPROTECT_MODE_WP as possible mode. > Signed-off-by: Peter Xu > --- > fs/userfaultfd.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c > index 455b87c0596f..e54ab6076e13 100644 > --- a/fs/userfaultfd.c > +++ b/fs/userfaultfd.c > @@ -1771,6 +1771,7 @@ static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx, > struct uffdio_writeprotect uffdio_wp; > struct uffdio_writeprotect __user *user_uffdio_wp; > struct userfaultfd_wake_range range; > + bool mode_wp, mode_dontwake; > > user_uffdio_wp = (struct uffdio_writeprotect __user *) arg; > > @@ -1786,17 +1787,19 @@ static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx, > if (uffdio_wp.mode & ~(UFFDIO_WRITEPROTECT_MODE_DONTWAKE | > UFFDIO_WRITEPROTECT_MODE_WP)) > return -EINVAL; > - if ((uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP) && > - (uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE)) > + > + mode_wp = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP; > + mode_dontwake = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE; > + > + if (mode_wp && mode_dontwake) > return -EINVAL; > > ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start, > - uffdio_wp.range.len, uffdio_wp.mode & > - UFFDIO_WRITEPROTECT_MODE_WP); > + uffdio_wp.range.len, mode_wp); > if (ret) > return ret; > > - if (!(uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE)) { > + if (!mode_wp && !mode_dontwake) { > range.start = uffdio_wp.range.start; > range.len = uffdio_wp.range.len; > wake_userfault(ctx, &range); > -- > 2.17.1 > -- Sincerely yours, Mike.