Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758010Ab3GRA6H (ORCPT ); Wed, 17 Jul 2013 20:58:07 -0400 Received: from mail-pa0-f54.google.com ([209.85.220.54]:46292 "EHLO mail-pa0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756626Ab3GRA6E (ORCPT ); Wed, 17 Jul 2013 20:58:04 -0400 Date: Wed, 17 Jul 2013 17:58:13 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Dave Hansen cc: Dave Jones , Andrew Morton , "Kirill A. Shutemov" , Andrea Arcangeli , Al Viro , Hugh Dickins , Wu Fengguang , Jan Kara , Mel Gorman , linux-mm@kvack.org, Andi Kleen , Matthew Wilcox , "Kirill A. Shutemov" , Hillf Danton , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 5/8] thp, mm: locking tail page is a bug In-Reply-To: <51E71E29.6030703@sr71.net> Message-ID: References: <1373885274-25249-1-git-send-email-kirill.shutemov@linux.intel.com> <1373885274-25249-6-git-send-email-kirill.shutemov@linux.intel.com> <20130717140953.7560e88e607f8f5df1b1fdd8@linux-foundation.org> <51E71E29.6030703@sr71.net> User-Agent: Alpine 2.00 (LNX 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1080 Lines: 26 On Wed, 17 Jul 2013, Dave Hansen wrote: > On 07/17/2013 02:09 PM, Andrew Morton wrote: > > lock_page() is a pretty commonly called function, and I assume quite a > > lot of people run with CONFIG_DEBUG_VM=y. > > > > Is the overhead added by this patch really worthwhile? > > I always thought of it as a developer-only thing. I don't think any of > the big distros turn it on by default. That's how I think of it too (and the problem is often that too few mm developers turn it on); but Dave Jones did confirm last November that Fedora turns it on. I believe Fedora turns it on to help us all, and wouldn't mind a mere VM_BUG_ON(PageTail(page)) in __lock_page() if it's helpful to Kirill. But if VM_BUG_ONs become expensive, I do think it's for Fedora to turn off CONFIG_DEBUG_VM, rather than for mm developers to avoid it. Hugh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/