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=-8.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 5901BC47E49 for ; Sat, 2 Nov 2019 11:24:05 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0F029222CE for ; Sat, 2 Nov 2019 11:24:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="UbbXzwi9" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0F029222CE Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 88A9E6B0005; Sat, 2 Nov 2019 07:24:04 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 83B3A6B0006; Sat, 2 Nov 2019 07:24:04 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 704D46B0007; Sat, 2 Nov 2019 07:24:04 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0157.hostedemail.com [216.40.44.157]) by kanga.kvack.org (Postfix) with ESMTP id 55B996B0005 for ; Sat, 2 Nov 2019 07:24:04 -0400 (EDT) Received: from smtpin25.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with SMTP id E3AB3181AEF15 for ; Sat, 2 Nov 2019 11:24:03 +0000 (UTC) X-FDA: 76111103166.25.car54_7aa78b5687d06 X-HE-Tag: car54_7aa78b5687d06 X-Filterd-Recvd-Size: 10120 Received: from us-smtp-1.mimecast.com (us-smtp-delivery-1.mimecast.com [207.211.31.120]) by imf45.hostedemail.com (Postfix) with ESMTP for ; Sat, 2 Nov 2019 11:24:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1572693842; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=jYxznwBlff51oTY0T/3kF9sJKP54f67dFipH+ZtQLPo=; b=UbbXzwi9gJAqJ9NKKgZU2UNqxv1c+0+TfNcgu2GXI0VrYCbImH44BM6eNO21KXxiBidEAp XvdOkimSUwS/GifulFKdxQfu3zs+Cuahfvh8eNtL902AlFscug1233eAq1d0PlxndM1cPD T0eRF/LW521PsNr6T3GLmVR2CYsTSo8= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-43-87shtdxlNnOYgmCCtnFLPg-1; Sat, 02 Nov 2019 07:23:58 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 906E32A3; Sat, 2 Nov 2019 11:23:56 +0000 (UTC) Received: from [10.36.116.109] (ovpn-116-109.ams2.redhat.com [10.36.116.109]) by smtp.corp.redhat.com (Postfix) with ESMTP id 533045C54A; Sat, 2 Nov 2019 11:23:53 +0000 (UTC) Subject: Re: [PATCH v2] mm/memory_hotplug: Fix try_offline_node() To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Tang Chen , Greg Kroah-Hartman , "Rafael J. Wysocki" , Andrew Morton , Keith Busch , Jiri Olsa , "Peter Zijlstra (Intel)" , Jani Nikula , Nayna Jain , Michal Hocko , Oscar Salvador , Stephen Rothwell , Dan Williams , Pavel Tatashin References: <20191101221118.5959-1-david@redhat.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <3e6849d9-b6d8-521b-394d-6747b85592f2@redhat.com> Date: Sat, 2 Nov 2019 12:23:52 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20191101221118.5959-1-david@redhat.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-MC-Unique: 87shtdxlNnOYgmCCtnFLPg-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable 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 01.11.19 23:11, David Hildenbrand wrote: > try_offline_node() is pretty much broken right now: > - The node span is updated when onlining memory, not when adding it. We > ignore memory that was mever onlined. Bad. > - We touch possible garbage memmaps. The pfn_to_nid(pfn) can easily > trigger a kernel panic. Bad for memory that is offline but also bad > for subsection hotadd with ZONE_DEVICE, whereby the memmap of the firs= t > PFN of a section might contain garbage. > - Sections belonging to mixed nodes are not properly considered. >=20 > As memory blocks might belong to multiple nodes, we would have to walk al= l > pageblocks (or at least subsections) within present sections. However, > we don't have a way to identify whether a memmap that is not online was > initialized (relevant for ZONE_DEVICE). This makes things more complicate= d. >=20 > Luckily, we can piggy pack on the node span and the nid stored in > memory blocks. Currently, the node span is grown when calling > move_pfn_range_to_zone() - e.g., when onlining memory, and shrunk when > removing memory, before calling try_offline_node(). Sysfs links are > created via link_mem_sections(), e.g., during boot or when adding memory. >=20 > If the node still spans memory or if any memory block belongs to the > nid, we don't set the node offline. As memory blocks that span multiple > nodes cannot get offlined, the nid stored in memory blocks is reliable > enough (for such online memory blocks, the node still spans the memory). >=20 > Note: We will soon stop shrinking the ZONE_DEVICE zone and the node span > when removing ZONE_DEVICE memory to fix similar issues (access of garbage > memmaps) - until we have a reliable way to identify whether these memmaps > were properly initialized. This implies later, that once a node had > ZONE_DEVICE memory, we won't be able to set a node offline - > which should be acceptable. >=20 > Since commit f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded > memory to zones until online") memory that is added is not assoziated > with a zone/node (memmap not initialized). The introducing > commit 60a5a19e7419 ("memory-hotplug: remove sysfs file of node") already > missed that we could have multiple nodes for a section and that the > zone/node span is updated when onlining pages, not when adding them. >=20 > I tested this by hotplugging two DIMMs to a memory-less and cpu-less NUMA > node. The node is properly onlined when adding the DIMMs. When removing > the DIMMs, the node is properly offlined. >=20 > Fixes: 60a5a19e7419 ("memory-hotplug: remove sysfs file of node") > Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memor= y to zones until online") # visiable after d0dc12e86b319 > Cc: Tang Chen > Cc: Greg Kroah-Hartman > Cc: "Rafael J. Wysocki" > Cc: Andrew Morton > Cc: Keith Busch > Cc: Jiri Olsa > Cc: "Peter Zijlstra (Intel)" > Cc: Jani Nikula > Cc: Nayna Jain > Cc: Michal Hocko > Cc: Oscar Salvador > Cc: Stephen Rothwell > Cc: Dan Williams > Cc: Pavel Tatashin > Signed-off-by: David Hildenbrand > --- >=20 > v1 -> v2: > - Drop sysfs handling, simplify, and add a comment > - Make sure to include last section fully >=20 > We stop shrinking the ZONE_DEVICE zone after the following patch: > [PATCH v6 04/10] mm/memory_hotplug: Don't access uninitialized memmaps > in shrink_zone_span() > This implies, the above note regarding ZONE_DEVICE on a node blocking a > node from getting offlined until we sorted out how to properly shrink > the ZONE_DEVICE zone. >=20 > This patch is especially important for: > [PATCH v6 05/10] mm/memory_hotplug: Shrink zones when offlining > memory > As the BUG fixed with this patch becomes now easier to observe when memor= y > is offlined (in contrast to when memory would never have been onlined > before). >=20 > As both patches are stable fixes and in next/master for a long time, we > should probably pull this patch in front of both and also backport this > patch at least to > Cc: stable@vger.kernel.org # v4.13+ > I have not checked yet if there are real blockers to do that. I guess not= . >=20 > --- > mm/memory_hotplug.c | 45 +++++++++++++++++++++++++++++---------------- > 1 file changed, 29 insertions(+), 16 deletions(-) >=20 > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 0140c20837b6..b5f696491577 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -1634,6 +1634,18 @@ static int check_cpu_on_node(pg_data_t *pgdat) > =09return 0; > } > =20 > +static int check_no_memblock_for_node_cb(struct memory_block *mem, void = *arg) > +{ > +=09int nid =3D *(int *)arg; > + > +=09/* > +=09 * If a memory block belongs to multiple nodes, the stored nid is not > +=09 * reliable. However, such blocks are always online (e.g., cannot get > +=09 * offlined) and, therefore, are still spanned by the node. > +=09 */ > +=09return mem->nid =3D=3D nid ? -EEXIST : 0; > +} > + > /** > * try_offline_node > * @nid: the node ID > @@ -1645,26 +1657,27 @@ static int check_cpu_on_node(pg_data_t *pgdat) > */ > void try_offline_node(int nid) > { > +=09const unsigned long end_section_nr =3D __highest_present_section_nr += 1; > =09pg_data_t *pgdat =3D NODE_DATA(nid); > -=09unsigned long start_pfn =3D pgdat->node_start_pfn; > -=09unsigned long end_pfn =3D start_pfn + pgdat->node_spanned_pages; > -=09unsigned long pfn; > - > -=09for (pfn =3D start_pfn; pfn < end_pfn; pfn +=3D PAGES_PER_SECTION) { > -=09=09unsigned long section_nr =3D pfn_to_section_nr(pfn); > - > -=09=09if (!present_section_nr(section_nr)) > -=09=09=09continue; > +=09int rc; > =20 > -=09=09if (pfn_to_nid(pfn) !=3D nid) > -=09=09=09continue; > +=09/* > +=09 * If the node still spans pages (especially ZONE_DEVICE), don't > +=09 * offline it. A node spans memory after move_pfn_range_to_zone(), > +=09 * e.g., after the memory block was onlined. > +=09 */ > +=09if (pgdat->node_spanned_pages) > +=09=09return; > =20 > -=09=09/* > -=09=09 * some memory sections of this node are not removed, and we > -=09=09 * can't offline node now. > -=09=09 */ > +=09/* > +=09 * Especially offline memory blocks might not be spanned by the > +=09 * node. They will get spanned by the node once they get onlined. > +=09 * However, they link to the node in sysfs and can get onlined later. > +=09 */ > +=09rc =3D walk_memory_blocks(0, PFN_PHYS(section_nr_to_pfn(end_section_n= r)), > +=09=09=09=09&nid, check_no_memblock_for_node_cb); walk_memory_block() might be fairly inefficient for this use case (as it=20 uses subsys_find_device_by_id() on any possible memory block, which is a=20 list scan). I guess I will introduce a walk_each_memory_block() that uses=20 bus_for_each_dev() under the hood. Sorry for the noise :) --=20 Thanks, David / dhildenb