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[91.12.103.110]) by smtp.gmail.com with ESMTPSA id a127sm9585796wme.40.2021.10.08.01.33.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 08 Oct 2021 01:33:14 -0700 (PDT) Subject: Re: [PATCH v1 3/3] memory-hotplug.rst: document the "auto-movable" online policy To: Mike Rapoport Cc: linux-kernel@vger.kernel.org, Andrew Morton , Jonathan Corbet , Michal Hocko , Oscar Salvador , linux-doc@vger.kernel.org, linux-mm@kvack.org References: <20210930144117.23641-1-david@redhat.com> <20210930144117.23641-4-david@redhat.com> <4bab9000-0b49-a852-d574-1c8b2fe10de1@redhat.com> From: David Hildenbrand Organization: Red Hat Message-ID: <09027675-5737-a076-7616-277aeb38427c@redhat.com> Date: Fri, 8 Oct 2021 10:33:13 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: E2E4E60022CF X-Stat-Signature: du9gixw97watz51c1efqkguhuz4p4x4g Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=IB28LEMA; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf10.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com X-HE-Tag: 1633681997-99767 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: >> It's essentially ignored with the auto-movable policy for memory hotplugged >> after boot (!MEMBLOCK_HOTPLUG). That's why only the description of >> "contig-zones" below describes how it interacts with the ``movable_node``, >> and we make it clear here that it's restricted to the "contig-zones" policy >> as well. >> >>
>> Bare metal, where we care about reliably unplugging hotplugged memory >> usually configures auto-onlining to "online_movable": for example, that's >> the case on RHEL. auto-movable doesn't make too much sense for bare metal: >> the nature of "movable_node" is to essentially online anything that might >> get hotunplugged MOVABLE, especially after hotplugging memory and rebooting: >> that is highly dangerous especially in virtualized environments. >> >> "auto-movable" is valuable in virtualized environments, where we add memory >> via: >> * add_memory_driver_managed() like virtio-mem, whereby such memory is >> never part of the firmware provided memory-map, so the policy is >> always in control even after a reboot. >> * Hotplugged virtual DIMMs, such as provided by x86-64/arm64, whereby we >> don't include these DIMMs in the firmware-provided memory map, but >> ACPI code adds them after early boot, making it behave similar to >> add_memory_driver_managed() -- the policy is always in control even >> after a reboot. >>
> > Do you want to put it somewhere in Documentation/ ? > It's already written anyway ;-) > I'll add to the "auto-movable" description: "This policy ignores the ``movable_node`` kernel command line parameter and isn't really applicable in environments that require it (e.g., bare metal with hotunpluggable nodes) where hotplugged memory might be exposed via the firmware-provided memory map early during boot to the system instead of getting detected, added and onlined later during boot (such as done by virito-mem or by some hypervisors implementing emulated DIMMs)." Thanks Mike! -- Thanks, David / dhildenb