Linux Virtualization - Apr 2020 - [PATCH v2 07/10] mm/memory_hotplug: Introduce offline_and_remove_memory()

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 at suse.com> [1]

[1] https://lkml.kernel.org/r/20200302142737.GP4380 at dhcp22.suse.cz

-- 
Thanks,

David / dhildenb

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 at suse.com> [1]
> 
> [1] https://lkml.kernel.org/r/20200302142737.GP4380 at dhcp22.suse.cz

Andrew, could you pls ack merging this through the vhost tree,
with the rest of the patchset?
> -- 
> Thanks,
> 
> David / dhildenb

On Tue, 14 Apr 2020 12:35:02 -0400 "Michael S. Tsirkin" <mst at
redhat.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 at suse.com> [1]
> > 
> > [1] https://lkml.kernel.org/r/20200302142737.GP4380 at 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 at linux-foundation.org>