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

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Message-ID: <874kul3dz4.fsf@vitty.brq.redhat.com>
Date:   Wed, 18 Mar 2020 16:00:15 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
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, 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>,
        Michal Hocko <mhocko@...nel.org>,
        Michal Hocko <mhocko@...e.com>,
        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

Baoquan He <bhe@...hat.com> writes:

> Is there a reason hyperV need boot with small memory, then enlarge it
> with huge memory? Since it's a real case in hyperV, I guess there must
> be reason, I am just curious.
>

It doesn't really *need* to but this can be utilized in e.g. 'hot
standby' schemes I believe. Also, it may be enough if the administrator
is just trying to e.g. double the size of RAM but the VM is already
under memory pressure. I wouldn't say that these cases are common but
afair bugs like 'I tried adding more memory to my VM and it just OOMed'
were reported in the past.

-- 
Vitaly