From owner-freebsd-bugs@freebsd.org Tue Sep 3 15:01:35 2019 Return-Path: Delivered-To: freebsd-bugs@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id A11C8D29C4 for ; Tue, 3 Sep 2019 15:01:35 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from mailman.nyi.freebsd.org (mailman.nyi.freebsd.org [IPv6:2610:1c1:1:606c::50:13]) by mx1.freebsd.org (Postfix) with ESMTP id 46N9C32m06z4TVN for ; Tue, 3 Sep 2019 15:01:35 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: by mailman.nyi.freebsd.org (Postfix) id 5B3FFD29C3; Tue, 3 Sep 2019 15:01:35 +0000 (UTC) Delivered-To: bugs@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 5AECCD29C2 for ; Tue, 3 Sep 2019 15:01:35 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) server-signature RSA-PSS (4096 bits) client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 46N9C310Jcz4TV4 for ; Tue, 3 Sep 2019 15:01:35 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from kenobi.freebsd.org (kenobi.freebsd.org [IPv6:2610:1c1:1:606c::50:1d]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id F11C149CF for ; Tue, 3 Sep 2019 15:01:34 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from kenobi.freebsd.org ([127.0.1.5]) by kenobi.freebsd.org (8.15.2/8.15.2) with ESMTP id x83F1Yt2075382 for ; Tue, 3 Sep 2019 15:01:34 GMT (envelope-from bugzilla-noreply@freebsd.org) Received: (from www@localhost) by kenobi.freebsd.org (8.15.2/8.15.2/Submit) id x83F1YPN075376 for bugs@FreeBSD.org; Tue, 3 Sep 2019 15:01:34 GMT (envelope-from bugzilla-noreply@freebsd.org) X-Authentication-Warning: kenobi.freebsd.org: www set sender to bugzilla-noreply@freebsd.org using -f From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 240061] MADV_FREE rewinds time to before fork() Date: Tue, 03 Sep 2019 15:01:33 +0000 X-Bugzilla-Reason: AssignedTo X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: Base System X-Bugzilla-Component: kern X-Bugzilla-Version: CURRENT X-Bugzilla-Keywords: X-Bugzilla-Severity: Affects Only Me X-Bugzilla-Who: markj@FreeBSD.org X-Bugzilla-Status: New X-Bugzilla-Resolution: X-Bugzilla-Priority: --- X-Bugzilla-Assigned-To: bugs@FreeBSD.org X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: https://bugs.freebsd.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: freebsd-bugs@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Bug reports List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 03 Sep 2019 15:01:35 -0000 https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D240061 --- Comment #6 from Mark Johnston --- One possible alternative is to convert MADV_FREE to MADV_DONTNEED if the ob= ject has a backing object. pmap_advise() needs to be updated to preserve the modified bits, but this should be fine since vm_page_advise(MADV_FREE) calls vm_page_undirty() anyway. Some basic testing on my workstation showed that virtually all calls to vm_object_madvise(MADV_FREE) are acting on an object with no backing object= .=20 Obviously this may not be true in general. # dtrace -n 'fbt::vm_object_madvise:entry /args[0] && args[3] =3D=3D 5/{@[args[0]->backing_object =3D=3D NULL] =3D count();}' ^C 0 13 1 17504 Untested patch here: https://people.freebsd.org/~markj/patches/madvise_cow.= diff --=20 You are receiving this mail because: You are the assignee for the bug.=