From owner-svn-src-stable-11@freebsd.org Sat Jul 23 21:56:53 2016 Return-Path: Delivered-To: svn-src-stable-11@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 58844BA2FE1; Sat, 23 Jul 2016 21:56:53 +0000 (UTC) (envelope-from alc@FreeBSD.org) Received: from repo.freebsd.org (repo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 2B19319D4; Sat, 23 Jul 2016 21:56:53 +0000 (UTC) (envelope-from alc@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id u6NLuqvq039347; Sat, 23 Jul 2016 21:56:52 GMT (envelope-from alc@FreeBSD.org) Received: (from alc@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id u6NLuq6I039346; Sat, 23 Jul 2016 21:56:52 GMT (envelope-from alc@FreeBSD.org) Message-Id: <201607232156.u6NLuq6I039346@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: alc set sender to alc@FreeBSD.org using -f From: Alan Cox Date: Sat, 23 Jul 2016 21:56:52 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-11@freebsd.org Subject: svn commit: r303251 - stable/11/sys/vm X-SVN-Group: stable-11 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-stable-11@freebsd.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: SVN commit messages for only the 11-stable src tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 23 Jul 2016 21:56:53 -0000 Author: alc Date: Sat Jul 23 21:56:52 2016 New Revision: 303251 URL: https://svnweb.freebsd.org/changeset/base/303251 Log: MFC r303101 Add a comment describing the 'fast path' that was introduced in r270011. Approved by: re (gjb) Modified: stable/11/sys/vm/vm_fault.c Directory Properties: stable/11/ (props changed) Modified: stable/11/sys/vm/vm_fault.c ============================================================================== --- stable/11/sys/vm/vm_fault.c Sat Jul 23 21:22:26 2016 (r303250) +++ stable/11/sys/vm/vm_fault.c Sat Jul 23 21:56:52 2016 (r303251) @@ -354,6 +354,15 @@ RetryFault:; KASSERT((fault_flags & VM_FAULT_WIRE) == 0, ("!wired && VM_FAULT_WIRE")); + /* + * Try to avoid lock contention on the top-level object through + * special-case handling of some types of page faults, specifically, + * those that are both (1) mapping an existing page from the top- + * level object and (2) not having to mark that object as containing + * dirty pages. Under these conditions, a read lock on the top-level + * object suffices, allowing multiple page faults of a similar type to + * run in parallel on the same top-level object. + */ if (fs.vp == NULL /* avoid locked vnode leak */ && (fault_flags & (VM_FAULT_WIRE | VM_FAULT_DIRTY)) == 0 && /* avoid calling vm_object_set_writeable_dirty() */