From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx145.postini.com [74.125.245.145]) by kanga.kvack.org (Postfix) with SMTP id 47D306B0033 for ; Wed, 17 Jul 2013 22:53:46 -0400 (EDT) Date: Wed, 17 Jul 2013 22:04:14 -0400 From: Dave Jones Subject: Re: [PATCH 5/8] thp, mm: locking tail page is a bug Message-ID: <20130718020414.GA1786@redhat.com> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: Dave Hansen , Andrew Morton , "Kirill A. Shutemov" , Andrea Arcangeli , Al Viro , 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 On Wed, Jul 17, 2013 at 05:58:13PM -0700, Hugh Dickins wrote: > 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. I'm ambivalent about whether we keep it on or off, we have no shortage of bugs to fix already, though I think as mentioned above, very few people actually enable it, so we're going to lose a lot of testing. Another idea, perhaps is an extra config option for more expensive debug options ? Dave -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org