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Thu, 10 Sep 2020 08:01:03 -0400 X-MC-Unique: Lf9liWlsNcSxsdSUk2WfEQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 87F82100831F; Thu, 10 Sep 2020 12:01:01 +0000 (UTC) Received: from [10.36.113.88] (ovpn-113-88.ams2.redhat.com [10.36.113.88]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2B61C702E7; Thu, 10 Sep 2020 12:00:59 +0000 (UTC) Subject: Re: [PATCH] mm: don't rely on system state to detect hot-plug operations To: Laurent Dufour , Michal Hocko Cc: akpm@linux-foundation.org, Oscar Salvador , rafael@kernel.org, nathanl@linux.ibm.com, cheloha@linux.ibm.com, stable@vger.kernel.org, Greg Kroah-Hartman , linux-mm@kvack.org, LKML References: <5cbd92e1-c00a-4253-0119-c872bfa0f2bc@redhat.com> <20200908170835.85440-1-ldufour@linux.ibm.com> <20200909074011.GD7348@dhcp22.suse.cz> <9faac1ce-c02d-7dbc-f79a-4aaaa5a73d28@linux.ibm.com> <20200909090953.GE7348@dhcp22.suse.cz> <4cdb54be-1a92-4ba4-6fee-3b415f3468a9@linux.ibm.com> <20200909105914.GF7348@dhcp22.suse.cz> <74a62b00-235e-7deb-2814-f3b240fea25e@linux.ibm.com> <20200910072331.GB28354@dhcp22.suse.cz> <31cfdf35-618f-6f56-ef16-0d999682ad02@linux.ibm.com> <20200910111246.GE28354@dhcp22.suse.cz> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Rspamd-Queue-Id: 33EE318229835 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 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 10.09.20 13:35, Laurent Dufour wrote: > Le 10/09/2020 =C3=A0 13:12, Michal Hocko a =C3=A9crit=C2=A0: >> On Thu 10-09-20 09:51:39, Laurent Dufour wrote: >>> Le 10/09/2020 =C3=A0 09:23, Michal Hocko a =C3=A9crit=C2=A0: >>>> On Wed 09-09-20 18:07:15, Laurent Dufour wrote: >>>>> Le 09/09/2020 =C3=A0 12:59, Michal Hocko a =C3=A9crit=C2=A0: >>>>>> On Wed 09-09-20 11:21:58, Laurent Dufour wrote: >>>> [...] >>>>>>> For the point a, using the enum allows to know in >>>>>>> register_mem_sect_under_node() if the link operation is due to a = hotplug >>>>>>> operation or done at boot time. >>>>>> >>>>>> Yes, but let me repeat. We have a mess here and different paths ch= eck >>>>>> for the very same condition by different ways. We need to unify th= ose. >>>>> >>>>> What are you suggesting to unify these checks (using a MP_* enum as >>>>> suggested by David, something else)? >>>> >>>> We do have system_state check spread at different places. I would us= e >>>> this one and wrap it behind a helper. Or have I missed any reason wh= y >>>> that wouldn't work for this case? >>> >>> That would not work in that case because memory can be hot-added at t= he >>> SYSTEM_SCHEDULING system state and the regular memory is also registe= red at >>> that system state too. So system state is not enough to discriminate = between >>> the both. >> >> If that is really the case all other places need a fix as well. >> Btw. could you be more specific about memory hotplug during early boot= ? >> How that happens? I am only aware of https://lkml.kernel.org/r/2020081= 8110046.6664-1-osalvador@suse.de >> and that doesn't happen as early as SYSTEM_SCHEDULING. >=20 > That points has been raised by David, quoting him here: >=20 >> IIRC, ACPI can hotadd memory while SCHEDULING, this patch would break = that. >> >> Ccing Oscar, I think he mentioned recently that this is the case with = ACPI. >=20 > Oscar told that he need to investigate further on that. >=20 > On my side I can't get these ACPI "early" hot-plug operations to happen= so I=20 > can't check that. >=20 > If this is clear that ACPI memory hotplug doesn't happen at SYSTEM_SCHE= DULING,=20 > the patch I proposed at first is enough to fix the issue. >=20 Booting a qemu guest with 4 coldplugged DIMMs gives me: :/root# dmesg | grep link_mem [ 0.302247] link_mem_sections() during 1 [ 0.445086] link_mem_sections() during 1 [ 0.445766] link_mem_sections() during 1 [ 0.446749] link_mem_sections() during 1 [ 0.447746] link_mem_sections() during 1 So AFAICs everything happens during SYSTEM_SCHEDULING - boot memory and ACPI (cold)plug. To make forward progress with this, relying on the system_state is obviously not sufficient. 1. We have to fix this instance and the instance directly in get_nid_for_pfn() by passing in the context (I once had a patch to clean that up, to not have two state checks, but it got lost somewhere). 2. The "system_state < SYSTEM_RUNNING" check in register_memory_resource() is correct. Actual memory hotplug after boot is not impacted. (I remember we discussed this exact behavior back then) 3. build_all_zonelists() should work as expected, called from start_kernel() before sched_init(). --=20 Thanks, David / dhildenb