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Thu, 10 Sep 2020 11:35:33 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6EA9DA4055; Thu, 10 Sep 2020 11:35:33 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B76CBA4051; Thu, 10 Sep 2020 11:35:32 +0000 (GMT) Received: from pomme.local (unknown [9.145.147.189]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 10 Sep 2020 11:35:32 +0000 (GMT) Subject: Re: [PATCH] mm: don't rely on system state to detect hot-plug operations To: Michal Hocko Cc: akpm@linux-foundation.org, David Hildenbrand , 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: Laurent Dufour Message-ID: Date: Thu, 10 Sep 2020 13:35:32 +0200 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20200910111246.GE28354@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687 definitions=2020-09-10_03:2020-09-10,2020-09-10 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 bulkscore=0 adultscore=0 lowpriorityscore=0 phishscore=0 clxscore=1015 malwarescore=0 spamscore=0 mlxlogscore=999 mlxscore=0 impostorscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009100107 X-Rspamd-Queue-Id: 38F12180AD804 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 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: 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 h= otplug >>>>>> operation or done at boot time. >>>>> >>>>> Yes, but let me repeat. We have a mess here and different paths che= ck >>>>> for the very same condition by different ways. We need to unify tho= se. >>>> >>>> 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 use >>> this one and wrap it behind a helper. Or have I missed any reason why >>> that wouldn't work for this case? >> >> That would not work in that case because memory can be hot-added at th= e >> SYSTEM_SCHEDULING system state and the regular memory is also register= ed at >> that system state too. So system state is not enough to discriminate b= etween >> the both. >=20 > 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/20200818= 110046.6664-1-osalvador@suse.de > and that doesn't happen as early as SYSTEM_SCHEDULING. That points has been raised by David, quoting him here: > IIRC, ACPI can hotadd memory while SCHEDULING, this patch would break t= hat. >=20 > Ccing Oscar, I think he mentioned recently that this is the case with A= CPI. Oscar told that he need to investigate further on that. On my side I can't get these ACPI "early" hot-plug operations to happen s= o I=20 can't check that. If this is clear that ACPI memory hotplug doesn't happen at SYSTEM_SCHEDU= LING,=20 the patch I proposed at first is enough to fix the issue.