From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f44.google.com (mail-pa0-f44.google.com [209.85.220.44]) by kanga.kvack.org (Postfix) with ESMTP id 153046B0035 for ; Wed, 27 Aug 2014 21:30:32 -0400 (EDT) Received: by mail-pa0-f44.google.com with SMTP id rd3so345580pab.31 for ; Wed, 27 Aug 2014 18:30:31 -0700 (PDT) Received: from mail-pa0-f42.google.com (mail-pa0-f42.google.com [209.85.220.42]) by mx.google.com with ESMTPS id yz5si3241628pbb.242.2014.08.27.18.30.30 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 27 Aug 2014 18:30:31 -0700 (PDT) Received: by mail-pa0-f42.google.com with SMTP id lf10so355996pab.29 for ; Wed, 27 Aug 2014 18:30:30 -0700 (PDT) Message-ID: <53FE8633.10305@amacapital.net> Date: Wed, 27 Aug 2014 18:30:27 -0700 From: Andy Lutomirski MIME-Version: 1.0 Subject: Re: [PATCH v10 00/21] Support ext4 on NV-DIMMs References: <20140827130613.c8f6790093d279a447196f17@linux-foundation.org> <20140827211250.GH3285@linux.intel.com> <20140827144622.ed81195a1d94799bb57a3207@linux-foundation.org> In-Reply-To: <20140827144622.ed81195a1d94799bb57a3207@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton , Matthew Wilcox Cc: Matthew Wilcox , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On 08/27/2014 02:46 PM, Andrew Morton wrote: > I assume (because I wasn't told!) that there are two objectives here: > > 1) reduce memory consumption by not maintaining pagecache and > 2) reduce CPU cost by avoiding the double-copies. > > These things are pretty easily quantified. And really they must be > quantified as part of the developer testing, because if you find > they've worsened then holy cow, what went wrong. > There are two more huge ones: 3) Writes via mmap are immediately durable (or at least they're durable after a *very* lightweight flush). 4) No page faults ever once a page is writable (I hope -- I'm not sure whether this series actually achieves that goal). A note on #3: there is ongoing work to enable write-through memory for things like this. Once that's done, then writes via mmap might actually be synchronously durable, depending on chipset details. --Andy -- 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