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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS 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 6EBB6C43219 for ; Thu, 25 Apr 2019 19:01:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C422F20678 for ; Thu, 25 Apr 2019 19:01:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730142AbfDYTBf (ORCPT ); Thu, 25 Apr 2019 15:01:35 -0400 Received: from mga01.intel.com ([192.55.52.88]:60888 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726715AbfDYTBe (ORCPT ); Thu, 25 Apr 2019 15:01:34 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by fmsmga101.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 25 Apr 2019 12:01:34 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.60,394,1549958400"; d="scan'208";a="134388328" Received: from ray.jf.intel.com (HELO [10.7.201.17]) ([10.7.201.17]) by orsmga007.jf.intel.com with ESMTP; 25 Apr 2019 12:01:33 -0700 Subject: Re: [v3 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, david@redhat.com References: <20190425175440.9354-1-pasha.tatashin@soleen.com> <20190425175440.9354-3-pasha.tatashin@soleen.com> From: Dave Hansen Openpgp: preference=signencrypt Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190425175440.9354-3-pasha.tatashin@soleen.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Pavel, Thanks for doing this! I knew we'd have to get to it eventually, but sounds like you needed it sooner rather than later. ... > 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..6f1640462df9 100644 > --- a/drivers/dax/kmem.c > +++ b/drivers/dax/kmem.c > @@ -71,21 +71,107 @@ 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 Instead of this #ifdef, is there any downside to doing if (!IS_ENABLED(CONFIG_MEMORY_HOTREMOVE)) { /* * Without hotremove, purposely leak ... */ return 0; } > +/* > + * 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. > + */ I'd much rather see comments inline with the code than all piled at the top of a function like this. One thing that would be helpful, though, is a reminder about needing the device hotplug lock. > +static int > +check_memblock_offlined_cb(struct memory_block *mem, void *arg) > +{ > + 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; The two devices confused me for a bit here. Seems worth a comment to remind the reader what this device _is_ versus 'mem_dev'. > + 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); I thought we had a magic resource printk %something. Could we just print one of the device resources here to save all the section/pfn/paddr calculations? Also, should we consider a slightly scarier message? This path has a permanent, user-visible effect (we can never try to unbind again). > + return -EBUSY; > + } > + > + return 0; > +} Even though they're static, I'd prefer that we not create two versions of check_memblock_offlined_cb() in the kernel. Can we give this a better, non-conflicting name? > +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; How could that happen? I can't think of any obvious scenarios. > + 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, > + check_memblock_offlined_cb); Does lock_device_hotplug() also lock memory online/offline? Otherwise, isn't this offline check racy? If not, can you please spell that out in a comment? Also, could you compare this a bit to the walk_memory_range() use in __remove_memory()? Why do we need two walks looking for offline blocks?