linux-kernel - Re: [PATCH v2 0/8] mm/memory_hotplug: allow to specify a default online

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Message-ID: <20200318135408.GP21362@dhcp22.suse.cz>
Date:   Wed, 18 Mar 2020 14:54:08 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Baoquan He <bhe@...hat.com>
Cc:     David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        linux-hyperv@...r.kernel.org,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Yumei Huang <yuhuang@...hat.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Eduardo Habkost <ehabkost@...hat.com>,
        Milan Zamazal <mzamazal@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Oscar Salvador <osalvador@...e.de>,
        Paul Mackerras <paulus@...ba.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>,
        Wei Yang <richard.weiyang@...il.com>
Subject: Re: [PATCH v2 0/8] mm/memory_hotplug: allow to specify a default
 online_type

On Wed 18-03-20 21:05:17, Baoquan He wrote:
> On 03/17/20 at 11:49am, David Hildenbrand wrote:
> > Distributions nowadays use udev rules ([1] [2]) to specify if and
> > how to online hotplugged memory. The rules seem to get more complex with
> > many special cases. Due to the various special cases,
> > CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE cannot be used. All memory hotplug
> > is handled via udev rules.
> > 
> > Everytime we hotplug memory, the udev rule will come to the same
> > conclusion. Especially Hyper-V (but also soon virtio-mem) add a lot of
> > memory in separate memory blocks and wait for memory to get onlined by user
> > space before continuing to add more memory blocks (to not add memory faster
> > than it is getting onlined). This of course slows down the whole memory
> > hotplug process.
> > 
> > To make the job of distributions easier and to avoid udev rules that get
> > more and more complicated, let's extend the mechanism provided by
> > - /sys/devices/system/memory/auto_online_blocks
> > - "memhp_default_state=" on the kernel cmdline
> > to be able to specify also "online_movable" as well as "online_kernel"
> 
> This patch series looks good, thanks. Since Andrew has merged it to -mm again,
> I won't add my Reviewed-by to bother. 

JFYI, Andrew usually adds R-b or A-b tags as they are posted.

-- 
Michal Hocko
SUSE Labs