From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx121.postini.com [74.125.245.121]) by kanga.kvack.org (Postfix) with SMTP id A51E26B0031 for ; Wed, 17 Jul 2013 20:58:03 -0400 (EDT) Received: by mail-pb0-f53.google.com with SMTP id xb12so2488488pbc.40 for ; Wed, 17 Jul 2013 17:58:02 -0700 (PDT) Date: Wed, 17 Jul 2013 17:58:13 -0700 (PDT) From: Hugh Dickins 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> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: 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 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, 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