From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753080AbZGWRYf (ORCPT ); Thu, 23 Jul 2009 13:24:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752508AbZGWRYe (ORCPT ); Thu, 23 Jul 2009 13:24:34 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:43425 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752472AbZGWRYd (ORCPT ); Thu, 23 Jul 2009 13:24:33 -0400 Date: Thu, 23 Jul 2009 10:23:16 -0700 From: Andrew Morton To: Mel Gorman Cc: Christoph Lameter , kosaki.motohiro@jp.fujitsu.com, maximlevitsky@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Lee.Schermerhorn@hp.com, penberg@cs.helsinki.fi, hannes@cmpxchg.org, jirislaby@gmail.com Subject: Re: [PATCH] mm: Warn once when a page is freed with PG_mlocked set V2 Message-Id: <20090723102316.b94a2e4f.akpm@linux-foundation.org> In-Reply-To: <20090723102938.GA27731@csn.ul.ie> References: <20090715125822.GB29749@csn.ul.ie> <20090722160649.61176c61.akpm@linux-foundation.org> <20090723102938.GA27731@csn.ul.ie> X-Mailer: Sylpheed 2.4.8 (GTK+ 2.12.5; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 23 Jul 2009 11:29:39 +0100 Mel Gorman wrote: > On Wed, Jul 22, 2009 at 04:06:49PM -0700, Andrew Morton wrote: > > On Wed, 15 Jul 2009 10:31:54 -0400 (EDT) > > Christoph Lameter wrote: > > > > > On Wed, 15 Jul 2009, Mel Gorman wrote: > > > > > > > -static inline int free_pages_check(struct page *page) > > > > +static inline int free_pages_check(struct page *page, int wasMlocked) > > > > { > > > > + WARN_ONCE(wasMlocked, KERN_WARNING > > > > + "Page flag mlocked set for process %s at pfn:%05lx\n" > > > > + "page:%p flags:0x%lX\n", > > > > + current->comm, page_to_pfn(page), > > > > + page, page->flags|__PG_MLOCKED); > > > > + > > > > if (unlikely(page_mapcount(page) | > > > > > > There is already a free_page_mlocked() that is only called if the mlock > > > bit is set. Move it into there to avoid having to run two checks in the > > > hot codee path? > > > > Agreed. > > > > This patch gratuitously adds hotpath overhead. Moving the change to be > > inside those preexisting wasMlocked tests will reduce its overhead a lot. > > > > It adds code duplication then, one of which is in a fast path. > > > As it stands, I'm really doubting that the patch's utility is worth its > > cost. > > > > I'm happy to let this one drop. It seemed like it would be nice for debugging > while there are still corner cases where mlocked pages are getting freed > instead of torn down but we already account for that situation occuring. While > I think it'll be tricky to spot, it's probably preferable to having warnings > spew out onto dmesg. If we do in it the way which Christoph recommends, the additional overhead is miniscule?