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[195.135.220.15]) by mx.google.com with ESMTPS id f25si10463315ede.206.2019.06.24.13.45.32 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 24 Jun 2019 13:45:32 -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 CC8C4AE34; Mon, 24 Jun 2019 20:45:31 +0000 (UTC) Message-ID: <1561409129.3058.1.camel@suse.de> Subject: Re: [PATCH v10 09/13] mm/sparsemem: Support sub-section hotplug From: Oscar Salvador To: Dan Williams , akpm@linux-foundation.org Cc: Michal Hocko , Vlastimil Babka , Logan Gunthorpe , Pavel Tatashin , linux-mm@kvack.org, linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org Date: Mon, 24 Jun 2019 22:45:29 +0200 In-Reply-To: <156092354368.979959.6232443923440952359.stgit@dwillia2-desk3.amr.corp.intel.com> References: <156092349300.979959.17603710711957735135.stgit@dwillia2-desk3.amr.corp.intel.com> <156092354368.979959.6232443923440952359.stgit@dwillia2-desk3.amr.corp.intel.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.26.1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit 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 Tue, 2019-06-18 at 22:52 -0700, Dan Williams wrote: > The libnvdimm sub-system has suffered a series of hacks and broken > workarounds for the memory-hotplug implementation's awkward > section-aligned (128MB) granularity. For example the following > backtrace > is emitted when attempting arch_add_memory() with physical address > ranges that intersect 'System RAM' (RAM) with 'Persistent Memory' > (PMEM) > within a given section: > > # cat /proc/iomem | grep -A1 -B1 Persistent\ Memory > 100000000-1ffffffff : System RAM > 200000000-303ffffff : Persistent Memory (legacy) > 304000000-43fffffff : System RAM > 440000000-23ffffffff : Persistent Memory > 2400000000-43bfffffff : Persistent Memory > 2400000000-43bfffffff : namespace2.0 > > WARNING: CPU: 38 PID: 928 at arch/x86/mm/init_64.c:850 > add_pages+0x5c/0x60 > [..] > RIP: 0010:add_pages+0x5c/0x60 > [..] > Call Trace: > devm_memremap_pages+0x460/0x6e0 > pmem_attach_disk+0x29e/0x680 [nd_pmem] > ? nd_dax_probe+0xfc/0x120 [libnvdimm] > nvdimm_bus_probe+0x66/0x160 [libnvdimm] > > It was discovered that the problem goes beyond RAM vs PMEM collisions > as > some platform produce PMEM vs PMEM collisions within a given section. > The libnvdimm workaround for that case revealed that the libnvdimm > section-alignment-padding implementation has been broken for a long > while. A fix for that long-standing breakage introduces as many > problems > as it solves as it would require a backward-incompatible change to > the > namespace metadata interpretation. Instead of that dubious route [1], > address the root problem in the memory-hotplug implementation. > > Note that EEXIST is no longer treated as success as that is how > sparse_add_section() reports subsection collisions, it was also > obviated > by recent changes to perform the request_region() for 'System RAM' > before arch_add_memory() in the add_memory() sequence. > > [1]: https://lore.kernel.org/r/155000671719.348031.234736316014111923 > 7.stgit@dwillia2-desk3.amr.corp.intel.com > Cc: Michal Hocko > Cc: Vlastimil Babka > Cc: Logan Gunthorpe > Cc: Oscar Salvador > Cc: Pavel Tatashin > Signed-off-by: Dan Williams Reviewed-by: Oscar Salvador -- Oscar Salvador SUSE L3