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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 C4D8CC10F11 for ; Wed, 24 Apr 2019 20:55:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 822A22183E for ; Wed, 24 Apr 2019 20:55:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387555AbfDXUzj (ORCPT ); Wed, 24 Apr 2019 16:55:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47782 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387467AbfDXUzi (ORCPT ); Wed, 24 Apr 2019 16:55:38 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id B0330308402F; Wed, 24 Apr 2019 20:55:37 +0000 (UTC) Received: from [10.36.116.32] (ovpn-116-32.ams2.redhat.com [10.36.116.32]) by smtp.corp.redhat.com (Postfix) with ESMTP id F09AA600C4; Wed, 24 Apr 2019 20:55:31 +0000 (UTC) Subject: Re: [v2 2/2] device-dax: "Hotremove" persistent memory that is used like normal RAM To: Pavel Tatashin , jmorris@namei.org, sashal@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-nvdimm@lists.01.org, akpm@linux-foundation.org, mhocko@suse.com, dave.hansen@linux.intel.com, dan.j.williams@intel.com, keith.busch@intel.com, vishal.l.verma@intel.com, dave.jiang@intel.com, zwisler@kernel.org, thomas.lendacky@amd.com, ying.huang@intel.com, fengguang.wu@intel.com, bp@suse.de, bhelgaas@google.com, baiyaowei@cmss.chinamobile.com, tiwai@suse.de, jglisse@redhat.com References: <20190421014429.31206-1-pasha.tatashin@soleen.com> <20190421014429.31206-3-pasha.tatashin@soleen.com> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190421014429.31206-3-pasha.tatashin@soleen.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.40]); Wed, 24 Apr 2019 20:55:38 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 21.04.19 03:44, Pavel Tatashin wrote: > It is now allowed to use persistent memory like a regular RAM, but > currently there is no way to remove this memory until machine is > rebooted. > > This work expands the functionality to also allows hotremoving > previously hotplugged persistent memory, and recover the device for use > for other purposes. > > To hotremove persistent memory, the management software must first > offline all memory blocks of dax region, and than unbind it from > device-dax/kmem driver. So, operations should look like this: > > echo offline > echo offline > /sys/devices/system/memory/memoryN/state > ... > echo dax0.0 > /sys/bus/dax/drivers/kmem/unbind > > Note: if unbind is done without offlining memory beforehand, it won't be > possible to do dax0.0 hotremove, and dax's memory is going to be part of > System RAM until reboot. > > Signed-off-by: Pavel Tatashin > --- > drivers/dax/dax-private.h | 2 + > drivers/dax/kmem.c | 91 +++++++++++++++++++++++++++++++++++++-- > 2 files changed, 89 insertions(+), 4 deletions(-) > > diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h > index a45612148ca0..999aaf3a29b3 100644 > --- a/drivers/dax/dax-private.h > +++ b/drivers/dax/dax-private.h > @@ -53,6 +53,7 @@ struct dax_region { > * @pgmap - pgmap for memmap setup / lifetime (driver owned) > * @ref: pgmap reference count (driver owned) > * @cmp: @ref final put completion (driver owned) > + * @dax_mem_res: physical address range of hotadded DAX memory > */ > struct dev_dax { > struct dax_region *region; > @@ -62,6 +63,7 @@ struct dev_dax { > struct dev_pagemap pgmap; > struct percpu_ref ref; > struct completion cmp; > + struct resource *dax_kmem_res; > }; > > static inline struct dev_dax *to_dev_dax(struct device *dev) > diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c > index 4c0131857133..d4896b281036 100644 > --- a/drivers/dax/kmem.c > +++ b/drivers/dax/kmem.c > @@ -71,21 +71,104 @@ int dev_dax_kmem_probe(struct device *dev) > kfree(new_res); > return rc; > } > + dev_dax->dax_kmem_res = new_res; > > return 0; > } > > +#ifdef CONFIG_MEMORY_HOTREMOVE > +/* > + * Check that device-dax's memory_blocks are offline. If a memory_block is not > + * offline a warning is printed and an error is returned. dax hotremove can > + * succeed only when every memory_block is offlined beforehand. > + */ > +static int > +offline_memblock_cb(struct memory_block *mem, void *arg) Function name suggests that you are actually trying to offline memory here. Maybe check_memblocks_offline_cb(), just like we have in mm/memory_hotplug.c. > +{ > + struct device *mem_dev = &mem->dev; > + bool is_offline; > + > + device_lock(mem_dev); > + is_offline = mem_dev->offline; > + device_unlock(mem_dev); > + > + if (!is_offline) { > + struct device *dev = (struct device *)arg; > + unsigned long spfn = section_nr_to_pfn(mem->start_section_nr); > + unsigned long epfn = section_nr_to_pfn(mem->end_section_nr); > + phys_addr_t spa = spfn << PAGE_SHIFT; > + phys_addr_t epa = epfn << PAGE_SHIFT; > + > + dev_warn(dev, "memory block [%pa-%pa] is not offline\n", > + &spa, &epa); > + > + return -EBUSY; > + } > + > + return 0; > +} > + > +static int dev_dax_kmem_remove(struct device *dev) > +{ > + struct dev_dax *dev_dax = to_dev_dax(dev); > + struct resource *res = dev_dax->dax_kmem_res; > + resource_size_t kmem_start; > + resource_size_t kmem_size; > + unsigned long start_pfn; > + unsigned long end_pfn; > + int rc; > + > + /* > + * dax kmem resource does not exist, means memory was never hotplugged. > + * So, nothing to do here. > + */ > + if (!res) > + return 0; > + > + kmem_start = res->start; > + kmem_size = resource_size(res); > + start_pfn = kmem_start >> PAGE_SHIFT; > + end_pfn = start_pfn + (kmem_size >> PAGE_SHIFT) - 1; > + > + /* > + * Walk and check that every singe memory_block of dax region is > + * offline > + */ > + lock_device_hotplug(); > + rc = walk_memory_range(start_pfn, end_pfn, dev, offline_memblock_cb); > + unlock_device_hotplug(); > + > + /* > + * If admin has not offlined memory beforehand, we cannot hotremove dax. > + * Unfortunately, because unbind will still succeed there is no way for > + * user to hotremove dax after this. > + */ > + if (rc) > + return rc; Can't it happen that there is a race between you checking if memory is offline and an admin onlining memory again? maybe pull the remove_memory() into the locked region, using __remove_memory() instead. > + > + /* Hotremove memory, cannot fail because memory is already offlined */ > + remove_memory(dev_dax->target_node, kmem_start, kmem_size); > + > + /* Release and free dax resources */ > + release_resource(res); > + kfree(res); > + dev_dax->dax_kmem_res = NULL; > + > + return 0; > +} > +#else > static int dev_dax_kmem_remove(struct device *dev) > { > /* > - * Purposely leak the request_mem_region() for the device-dax > - * range and return '0' to ->remove() attempts. The removal of > - * the device from the driver always succeeds, but the region > - * is permanently pinned as reserved by the unreleased > + * Without hotremove purposely leak the request_mem_region() for the > + * device-dax range and return '0' to ->remove() attempts. The removal > + * of the device from the driver always succeeds, but the region is > + * permanently pinned as reserved by the unreleased > * request_mem_region(). > */ > return 0; > } > +#endif /* CONFIG_MEMORY_HOTREMOVE */ > > static struct dax_device_driver device_dax_kmem_driver = { > .drv = { > -- Thanks, David / dhildenb