From owner-cvs-src-old@FreeBSD.ORG Mon May 31 01:43:11 2010 Return-Path: Delivered-To: cvs-src-old@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id D195C106567C for ; Mon, 31 May 2010 01:43:11 +0000 (UTC) (envelope-from alc@FreeBSD.org) Received: from repoman.freebsd.org (unknown [IPv6:2001:4f8:fff6::29]) by mx1.freebsd.org (Postfix) with ESMTP id BEDC48FC08 for ; Mon, 31 May 2010 01:43:11 +0000 (UTC) Received: from repoman.freebsd.org (localhost [127.0.0.1]) by repoman.freebsd.org (8.14.3/8.14.3) with ESMTP id o4V1hBPj055471 for ; Mon, 31 May 2010 01:43:11 GMT (envelope-from alc@repoman.freebsd.org) Received: (from svn2cvs@localhost) by repoman.freebsd.org (8.14.3/8.14.3/Submit) id o4V1hBwl055470 for cvs-src-old@freebsd.org; Mon, 31 May 2010 01:43:11 GMT (envelope-from alc@repoman.freebsd.org) Message-Id: <201005310143.o4V1hBwl055470@repoman.freebsd.org> X-Authentication-Warning: repoman.freebsd.org: svn2cvs set sender to alc@repoman.freebsd.org using -f From: Alan Cox Date: Mon, 31 May 2010 01:43:02 +0000 (UTC) To: cvs-src-old@freebsd.org X-FreeBSD-CVS-Branch: HEAD Subject: cvs commit: src/sys/mips/mips pmap.c X-BeenThere: cvs-src-old@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: **OBSOLETE** CVS commit messages for the src tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 31 May 2010 01:43:11 -0000 alc 2010-05-31 01:43:02 UTC FreeBSD src repository Modified files: sys/mips/mips pmap.c Log: SVN rev 208665 on 2010-05-31 01:43:02Z by alc Merge portions of r208645 and supporting code from the i386 pmap: When I pushed down the page queues lock into pmap_is_modified(), I created an ordering dependence: A pmap operation that clears PG_WRITEABLE and calls vm_page_dirty() must perform the call first. Otherwise, pmap_is_modified() could return FALSE without acquiring the page queues lock because the page is not (currently) writeable, and the caller to pmap_is_modified() might believe that the page's dirty field is clear because it has not seen the effect of the vm_page_dirty() call. When I pushed down the page queues lock into pmap_is_modified(), I overlooked one place where this ordering dependence is violated: pmap_enter(). In a rare situation pmap_enter() can be called to replace a dirty mapping to one page with a mapping to another page. (I say rare because replacements generally occur as a result of a copy-on-write fault, and so the old page is not dirty.) This change delays clearing PG_WRITEABLE until after vm_page_dirty() has been called. Fixing the ordering dependency also makes it easy to introduce a small optimization: When pmap_enter() used to replace a mapping to one page with a mapping to another page, it freed the pv entry for the first mapping and later called the pv entry allocator for the new mapping. Now, pmap_enter() attempts to recycle the old pv entry, saving two calls to the pv entry allocator. Revision Changes Path 1.57 +45 -34 src/sys/mips/mips/pmap.c