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=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=unavailable 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 BAAB6C04AB5 for ; Thu, 6 Jun 2019 17:34:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9013E2083D for ; Thu, 6 Jun 2019 17:34:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730163AbfFFReZ (ORCPT ); Thu, 6 Jun 2019 13:34:25 -0400 Received: from mx2.suse.de ([195.135.220.15]:33886 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726924AbfFFReZ (ORCPT ); Thu, 6 Jun 2019 13:34:25 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 5384EAE4D; Thu, 6 Jun 2019 17:34:24 +0000 (UTC) Date: Thu, 6 Jun 2019 19:34:21 +0200 From: Oscar Salvador To: Dan Williams Cc: akpm@linux-foundation.org, Michal Hocko , Vlastimil Babka , Logan Gunthorpe , Pavel Tatashin , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , linux-mm@kvack.org, linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v9 01/12] mm/sparsemem: Introduce struct mem_section_usage Message-ID: <20190606173421.GD31194@linux> References: <155977186863.2443951.9036044808311959913.stgit@dwillia2-desk3.amr.corp.intel.com> <155977187407.2443951.16503493275720588454.stgit@dwillia2-desk3.amr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <155977187407.2443951.16503493275720588454.stgit@dwillia2-desk3.amr.corp.intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 05, 2019 at 02:57:54PM -0700, Dan Williams wrote: > Towards enabling memory hotplug to track partial population of a > section, introduce 'struct mem_section_usage'. > > A pointer to a 'struct mem_section_usage' instance replaces the existing > pointer to a 'pageblock_flags' bitmap. Effectively it adds one more > 'unsigned long' beyond the 'pageblock_flags' (usemap) allocation to > house a new 'subsection_map' bitmap. The new bitmap enables the memory > hot{plug,remove} implementation to act on incremental sub-divisions of a > section. > > The default SUBSECTION_SHIFT is chosen to keep the 'subsection_map' no > larger than a single 'unsigned long' on the major architectures. > Alternatively an architecture can define ARCH_SUBSECTION_SHIFT to > override the default PMD_SHIFT. Note that PowerPC needs to use > ARCH_SUBSECTION_SHIFT to workaround PMD_SHIFT being a non-constant > expression on PowerPC. > > The primary motivation for this functionality is to support platforms > that mix "System RAM" and "Persistent Memory" within a single section, > or multiple PMEM ranges with different mapping lifetimes within a single > section. The section restriction for hotplug has caused an ongoing saga > of hacks and bugs for devm_memremap_pages() users. > > Beyond the fixups to teach existing paths how to retrieve the 'usemap' > from a section, and updates to usemap allocation path, there are no > expected behavior changes. > > Cc: Michal Hocko > Cc: Vlastimil Babka > Cc: Logan Gunthorpe > Cc: Oscar Salvador > Cc: Pavel Tatashin > Cc: Benjamin Herrenschmidt > Cc: Paul Mackerras > Cc: Michael Ellerman > Signed-off-by: Dan Williams Reviewed-by: Oscar Salvador -- Oscar Salvador SUSE L3