From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C3BF9ECE566 for ; Wed, 19 Sep 2018 22:26:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6E7DF2146E for ; Wed, 19 Sep 2018 22:26:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6E7DF2146E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726123AbeITEGI (ORCPT ); Thu, 20 Sep 2018 00:06:08 -0400 Received: from mga06.intel.com ([134.134.136.31]:6642 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725834AbeITEGH (ORCPT ); Thu, 20 Sep 2018 00:06:07 -0400 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga104.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 19 Sep 2018 15:26:05 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.53,395,1531810800"; d="scan'208";a="84965431" Received: from unknown (HELO localhost.localdomain) ([10.232.112.44]) by orsmga003.jf.intel.com with ESMTP; 19 Sep 2018 15:24:27 -0700 Date: Wed, 19 Sep 2018 16:26:22 -0600 From: Keith Busch To: Dave Hansen Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Kirill Shutemov , Dan Williams Subject: Re: [PATCH 0/7] mm: faster get user pages Message-ID: <20180919222621.GA29003@localhost.localdomain> References: <20180919210250.28858-1-keith.busch@intel.com> <40b392d0-0642-2d9b-5325-664a328ff677@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <40b392d0-0642-2d9b-5325-664a328ff677@intel.com> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 19, 2018 at 02:15:28PM -0700, Dave Hansen wrote: > On 09/19/2018 02:02 PM, Keith Busch wrote: > > Pinning user pages out of nvdimm dax memory is significantly slower > > compared to system ram. Analysis points to software overhead incurred > > from a radix tree lookup. This patch series fixes that by removing the > > relatively costly dev_pagemap lookup that was repeated for each page, > > significantly increasing gup time. > > Could you also remind us why DAX pages are such special snowflakes and > *require* radix tree lookups in the first place? Yeah, ZONE_DEVICE memory is special. It has struct page mappings, but not for online general use. The dev_pagemap is the metadata to the zone device memory, and that metadata is stashed in a radix tree. We're looking up the dev_pagemap in this path to take a reference so the zone device can't be unmapped.