linux-kernel - Re: [PATCH v2 07/10] mm/memory_hotplug: Introduce offline_and_remove

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Message-Id: <20200414173046.dc097faf7062f76a8c68f580@linux-foundation.org>
Date:   Tue, 14 Apr 2020 17:30:46 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, virtio-dev@...ts.oasis-open.org,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        Michal Hocko <mhocko@...nel.org>,
        Oscar Salvador <osalvador@...e.com>,
        Michal Hocko <mhocko@...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 v2 07/10] mm/memory_hotplug: Introduce
 offline_and_remove_memory()

On Tue, 14 Apr 2020 12:35:02 -0400 "Michael S. Tsirkin" <mst@...hat.com> wrote:

> On Wed, Mar 11, 2020 at 06:19:04PM +0100, David Hildenbrand wrote:
> > On 11.03.20 18:14, 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 is an interface to offline and remove the memory from kernel
> > > module context, where we don't have access to the memory block devices
> > > (esp. find_memory_block() and device_offline()) and the device hotplug
> > > lock.
> > > 
> > > To keep things simple, allow to only work on a single memory block.
> > > 
> > 
> > Lost the ACK from Michael
> > 
> > Acked-by: Michal Hocko <mhocko@...e.com> [1]
> > 
> > [1] https://lkml.kernel.org/r/20200302142737.GP4380@dhcp22.suse.cz
> 
> 
> Andrew, could you pls ack merging this through the vhost tree,
> with the rest of the patchset?

I wish the device_offline() return value was documented :(

Yes, please go ahead and merge.

Acked-by: Andrew Morton <akpm@...ux-foundation.org>