linux-kernel - Re: [PATCH v2 00/28] The new cgroup slab memory controller

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Date:   Wed, 2 Sep 2020 06:39:07 -0400 (EDT)
From:   David Hildenbrand <dhildenb@...hat.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Pavel Tatashin <pasha.tatashin@...een.com>,
        Roman Gushchin <guro@...com>,
        Bharata B Rao <bharata@...ux.ibm.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        Yafang Shao <laoar.shao@...il.com>,
        stable <stable@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH v2 00/28] The new cgroup slab memory controller



> Am 02.09.2020 um 11:53 schrieb Vlastimil Babka <vbabka@...e.cz>:
> 
> On 8/28/20 6:47 PM, Pavel Tatashin wrote:
>> There appears to be another problem that is related to the
>> cgroup_mutex -> mem_hotplug_lock deadlock described above.
>> 
>> In the original deadlock that I described, the workaround is to
>> replace crash dump from piping to Linux traditional save to files
>> method. However, after trying this workaround, I still observed
>> hardware watchdog resets during machine  shutdown.
>> 
>> The new problem occurs for the following reason: upon shutdown systemd
>> calls a service that hot-removes memory, and if hot-removing fails for
> 
> Why is that hotremove even needed if we're shutting down? Are there any
> (virtualization?) platforms where it makes some difference over plain
> shutdown/restart?

If all it‘s doing is offlining random memory that sounds unnecessary and dangerous. Any pointers to this service so we can figure out what it‘s doing and why? (Arch? Hypervisor?)