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[195.135.220.15]) by mx.google.com with ESMTPS id i21si2721119edg.433.2019.06.26.01.27.59 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 26 Jun 2019 01:27:59 -0700 (PDT) Received-SPF: pass (google.com: domain of osalvador@suse.de designates 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=pass (google.com: domain of osalvador@suse.de designates 195.135.220.15 as permitted sender) smtp.mailfrom=osalvador@suse.de 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) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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