linux-kernel - Re: [PATCH RFC 7/8] mm: allow to control onlining/offlining of memory by a driver

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Message-ID: <92ff9057-7f1e-d9b7-610e-0a7022b8da01@redhat.com>
Date:   Fri, 13 Apr 2018 18:32:39 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-mm@...ck.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:XEN HYPERVISOR INTERFACE" 
        <xen-devel@...ts.xenproject.org>
Subject: Re: [PATCH RFC 7/8] mm: allow to control onlining/offlining of memory
 by a driver

On 13.04.2018 17:59, Michal Hocko wrote:
> On Fri 13-04-18 15:33:28, David Hildenbrand wrote:
>> Some devices (esp. paravirtualized) might want to control
>> - when to online/offline a memory block
>> - how to online memory (MOVABLE/NORMAL)
>> - in which granularity to online/offline memory
>>
>> So let's add a new flag "driver_managed" and disallow to change the
>> state by user space. Device onlining/offlining will still work, however
>> the memory will not be actually onlined/offlined. That has to be handled
>> by the device driver that owns the memory.
> 
> Is there any reason to create the memblock sysfs interface to this
> memory at all? ZONE_DEVICE mem hotplug users currently do not do that
> and manage the memory themselves. It seems you want to achieve the same
> thing, no?
> 

Yes, I think so, namely kdump. We have to retrigger kexec() whenever a
memory block is added/removed. udev events are sent for that reason when
a memory block is created/deleted. And I think this is not done for
ZONE_DEVICE devices, or am I wrong?

-- 

Thanks,

David / dhildenb