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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 0CB8FC48BD3 for ; Wed, 26 Jun 2019 08:28:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DCBAB208E3 for ; Wed, 26 Jun 2019 08:28:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726988AbfFZI2A (ORCPT ); Wed, 26 Jun 2019 04:28:00 -0400 Received: from mx2.suse.de ([195.135.220.15]:60496 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725379AbfFZI17 (ORCPT ); Wed, 26 Jun 2019 04:27:59 -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 AD0FBAD7E; Wed, 26 Jun 2019 08:27:58 +0000 (UTC) Date: Wed, 26 Jun 2019 10:27:56 +0200 From: Oscar Salvador To: David Hildenbrand Cc: akpm@linux-foundation.org, mhocko@suse.com, dan.j.williams@intel.com, pasha.tatashin@soleen.com, Jonathan.Cameron@huawei.com, anshuman.khandual@arm.com, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 0/5] Allocate memmap from hotadded memory Message-ID: <20190626082756.GD30863@linux> References: <20190625075227.15193-1-osalvador@suse.de> <2ebfbd36-11bd-9576-e373-2964c458185b@redhat.com> <20190626080249.GA30863@linux> <2750c11a-524d-b248-060c-49e6b3eb8975@redhat.com> <20190626081516.GC30863@linux> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190626081516.GC30863@linux> 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 26, 2019 at 10:15:16AM +0200, Oscar Salvador wrote: > On Wed, Jun 26, 2019 at 10:11:06AM +0200, David Hildenbrand wrote: > > Back then, I already mentioned that we might have some users that > > remove_memory() they never added in a granularity it wasn't added. My > > concerns back then were never fully sorted out. > > > > arch/powerpc/platforms/powernv/memtrace.c > > > > - Will remove memory in memory block size chunks it never added > > - What if that memory resides on a DIMM added via MHP_MEMMAP_DEVICE? > > > > Will it at least bail out? Or simply break? > > > > IOW: I am not yet 100% convinced that MHP_MEMMAP_DEVICE is save to be > > introduced. > > Uhm, I will take a closer look and see if I can clear your concerns. > TBH, I did not try to use arch/powerpc/platforms/powernv/memtrace.c > yet. > > I will get back to you once I tried it out. On a second though, it would be quite trivial to implement a check in remove_memory() that does not allow to remove memory used with MHP_MEMMAP_DEVICE in a different granularity: +static bool check_vmemmap_granularity(u64 start, u64 size); +{ + unsigned long pfn; + unsigned int nr_pages; + struct page *p; + + pfn = PHYS_PFN(start); + p = pfn_to_page(pfn); + nr_pages = size >> PAGE_SIZE; + + if (PageVmemmap(p)) { + struct page *h = vmemmap_get_head(p); + unsigned long sections = (unsigned long)h->private; + + if (sections * PAGES_PER_SECTION > nr_pages) + fail; + } + no_fail; +} + + static int __ref try_remove_memory(int nid, u64 start, u64 size) { int rc = 0; BUG_ON(check_hotplug_memory_range(start, size)); mem_hotplug_begin(); + rc = check_vmemmap_granularity(start, size); + if (rc) + goto done; The above is quite hacky, but it gives an idea. I will try the code from arch/powerpc/platforms/powernv/memtrace.c and see how can I implement a check. -- Oscar Salvador SUSE L3