From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f177.google.com (mail-pd0-f177.google.com [209.85.192.177]) by kanga.kvack.org (Postfix) with ESMTP id 05D896B0071 for ; Thu, 27 Feb 2014 17:08:15 -0500 (EST) Received: by mail-pd0-f177.google.com with SMTP id g10so2965484pdj.8 for ; Thu, 27 Feb 2014 14:08:15 -0800 (PST) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTP id q5si6008871pbh.74.2014.02.27.14.08.14 for ; Thu, 27 Feb 2014 14:08:15 -0800 (PST) Date: Thu, 27 Feb 2014 14:08:13 -0800 From: Andrew Morton Subject: Re: [PATCHv3 1/2] mm: introduce vm_ops->map_pages() Message-Id: <20140227140813.988b225351b91937f840404b@linux-foundation.org> In-Reply-To: <530FB55F.2070106@linux.intel.com> References: <1393530827-25450-1-git-send-email-kirill.shutemov@linux.intel.com> <1393530827-25450-2-git-send-email-kirill.shutemov@linux.intel.com> <530FB55F.2070106@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: "Kirill A. Shutemov" , Linus Torvalds , Mel Gorman , Rik van Riel , Andi Kleen , Matthew Wilcox , Alexander Viro , Dave Chinner , Ning Qu , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org On Thu, 27 Feb 2014 13:59:59 -0800 Dave Hansen wrote: > On 02/27/2014 11:53 AM, Kirill A. Shutemov wrote: > > +#define FAULT_AROUND_ORDER 4 > > +#define FAULT_AROUND_PAGES (1UL << FAULT_AROUND_ORDER) > > +#define FAULT_AROUND_MASK ~((1UL << (PAGE_SHIFT + FAULT_AROUND_ORDER)) - 1) > > Looking at the performance data made me think of this: do we really want > this to be static? It seems like the kind of thing that will cause a > regression _somewhere_. Yes, allowing people to tweak it at runtime would improve testability a lot. I don't think we want to let yet another tunable out into the wild unless we really need to - perhaps a not-for-mainline add-on patch, or something in debugfs so we have the option of taking it away later. > Also, the folks with larger base bage sizes probably don't want a > FAULT_AROUND_ORDER=4. That's 1MB of fault-around for ppc64, for example. Yup, we don't want the same app to trigger dramatically different kernel behaviour when it is moved from x86 to ppc. -- 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