From owner-svn-src-user@FreeBSD.ORG Sun Jun 16 18:31:13 2013 Return-Path: Delivered-To: svn-src-user@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by hub.freebsd.org (Postfix) with ESMTP id F26B072C; Sun, 16 Jun 2013 18:31:12 +0000 (UTC) (envelope-from attilio@FreeBSD.org) Received: from svn.freebsd.org (svn.freebsd.org [IPv6:2001:1900:2254:2068::e6a:0]) by mx1.freebsd.org (Postfix) with ESMTP id E467512C3; Sun, 16 Jun 2013 18:31:12 +0000 (UTC) Received: from svn.freebsd.org ([127.0.1.70]) by svn.freebsd.org (8.14.7/8.14.7) with ESMTP id r5GIVCeQ031048; Sun, 16 Jun 2013 18:31:12 GMT (envelope-from attilio@svn.freebsd.org) Received: (from attilio@localhost) by svn.freebsd.org (8.14.7/8.14.5/Submit) id r5GIVCZ3031047; Sun, 16 Jun 2013 18:31:12 GMT (envelope-from attilio@svn.freebsd.org) Message-Id: <201306161831.r5GIVCZ3031047@svn.freebsd.org> From: Attilio Rao Date: Sun, 16 Jun 2013 18:31:12 +0000 (UTC) To: src-committers@freebsd.org, svn-src-user@freebsd.org Subject: svn commit: r251813 - user/attilio/vmobj-readlock/sys/vm X-SVN-Group: user MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-user@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: "SVN commit messages for the experimental " user" src tree" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 16 Jun 2013 18:31:13 -0000 Author: attilio Date: Sun Jun 16 18:31:12 2013 New Revision: 251813 URL: http://svnweb.freebsd.org/changeset/base/251813 Log: Tentatively document the hard/soft busy logic. Sponsored by: EMC / Isilon storage division Modified: user/attilio/vmobj-readlock/sys/vm/vm_page.h Modified: user/attilio/vmobj-readlock/sys/vm/vm_page.h ============================================================================== --- user/attilio/vmobj-readlock/sys/vm/vm_page.h Sun Jun 16 18:27:53 2013 (r251812) +++ user/attilio/vmobj-readlock/sys/vm/vm_page.h Sun Jun 16 18:31:12 2013 (r251813) @@ -109,6 +109,17 @@ * contains the dirty field. In the machine-independent layer, * the implementation of read-modify-write operations on the * field is encapsulated in vm_page_clear_dirty_mask(). + * + * Page content access is regulated (mostly) by the busy mechanism. + * When the page content is changing (for example, during a page READ + * operation) the page owner must acquire an hard busy token. Similarly, + * when the page content is just being accessed for reading purposes + * (for example, during a page WRITE operation) the page owner must + * acquire a soft busy token. + * The hard busy mechanism is controlled using vm_page_busy() and + * vm_page_unbusy() interfaces. Likewise the soft busy mechanism is + * controlled through the usage of vm_page_io_start() and + * vm_page_io_finish(). */ #if PAGE_SIZE == 4096