linux-kernel - Re: [PATCH RFC v3 8/9] mm/memory_hotplug: Introduce offline_and_remove

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Message-ID: <20191016114708.GY317@dhcp22.suse.cz>
Date:   Wed, 16 Oct 2019 13:47:08 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        virtualization@...ts.linux-foundation.org,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Wei Yang <richard.weiyang@...il.com>,
        Dan Williams <dan.j.williams@...el.com>, Qian Cai <cai@....pw>
Subject: Re: [PATCH RFC v3 8/9] mm/memory_hotplug: Introduce
 offline_and_remove_memory()

On Thu 19-09-19 16:22:27, David Hildenbrand wrote:
> virtio-mem wants to offline and remove a memory block once it unplugged
> all subblocks (e.g., using alloc_contig_range()). Let's provide
> an interface to do that from a driver. virtio-mem already supports to
> offline partially unplugged memory blocks. Offlining a fully unplugged
> memory block will not require to migrate any pages. All unplugged
> subblocks are PageOffline() and have a reference count of 0 - so
> offlining code will simply skip them.
> 
> All we need an interface to trigger the "offlining" and the removing in a
> single operation - to make sure the memory block cannot get onlined by
> user space again before it gets removed.
> 
> To keep things simple, allow to only work on a single memory block.

Without a user it is not really clear why do we need this interface.
I am also not really sure why do you want/need to control beyond the
offlining stage. Care to explain some more?
-- 
Michal Hocko
SUSE Labs