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[209.132.183.28]) by mx.google.com with ESMTPS id d3si4492591qkk.167.2019.06.26.01.38.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 26 Jun 2019 01:38:08 -0700 (PDT) Received-SPF: pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 296DE3086213; Wed, 26 Jun 2019 08:37:55 +0000 (UTC) Received: from [10.36.116.174] (ovpn-116-174.ams2.redhat.com [10.36.116.174]) by smtp.corp.redhat.com (Postfix) with ESMTP id ED3CA5D71B; Wed, 26 Jun 2019 08:37:50 +0000 (UTC) Subject: Re: [PATCH v2 0/5] Allocate memmap from hotadded memory To: Oscar Salvador 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 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> <20190626082756.GD30863@linux> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190626082756.GD30863@linux> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Wed, 26 Jun 2019 08:38:07 +0000 (UTC) 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 26.06.19 10:27, Oscar Salvador wrote: > 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. > Yeah, I would consider such a safety check mandatory for MHP_MEMMAP_DEVICE. -- Thanks, David / dhildenb