From owner-svn-src-head@freebsd.org Wed Jul 20 17:20:23 2016 Return-Path: Delivered-To: svn-src-head@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 86B6DB9F60A; Wed, 20 Jul 2016 17:20:23 +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 59E4A14E5; Wed, 20 Jul 2016 17:20:23 +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 u6KHKMYh018496; Wed, 20 Jul 2016 17:20:22 GMT (envelope-from alc@FreeBSD.org) Received: (from alc@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id u6KHKMOZ018495; Wed, 20 Jul 2016 17:20:22 GMT (envelope-from alc@FreeBSD.org) Message-Id: <201607201720.u6KHKMOZ018495@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: alc set sender to alc@FreeBSD.org using -f From: Alan Cox Date: Wed, 20 Jul 2016 17:20:22 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r303101 - head/sys/vm X-SVN-Group: head MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 20 Jul 2016 17:20:23 -0000 Author: alc Date: Wed Jul 20 17:20:22 2016 New Revision: 303101 URL: https://svnweb.freebsd.org/changeset/base/303101 Log: Add a comment describing the 'fast path' that was introduced in r270011. Reviewed by: kib MFC after: 3 days Sponsored by: EMC / Isilon Storage Division Modified: head/sys/vm/vm_fault.c Modified: head/sys/vm/vm_fault.c ============================================================================== --- head/sys/vm/vm_fault.c Wed Jul 20 17:19:47 2016 (r303100) +++ head/sys/vm/vm_fault.c Wed Jul 20 17:20:22 2016 (r303101) @@ -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() */