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SubjectRe: [PATCH v2 07/10] mm/memory_hotplug: Introduce offline_and_remove_memory()
> 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.
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Oscar Salvador <osalvador@suse.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> Cc: Wei Yang <richard.weiyang@gmail.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Qian Cai <cai@lca.pw>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> include/linux/memory_hotplug.h | 1 +
> mm/memory_hotplug.c | 37 ++++++++++++++++++++++++++++++++++
> 2 files changed, 38 insertions(+)
>
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index f4d59155f3d4..a98aa16dbfa1 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -311,6 +311,7 @@ extern void try_offline_node(int nid);
> extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages);
> extern int remove_memory(int nid, u64 start, u64 size);
> extern void __remove_memory(int nid, u64 start, u64 size);
> +extern int offline_and_remove_memory(int nid, u64 start, u64 size);
>
> #else
> static inline bool is_mem_section_removable(unsigned long pfn,
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index ab1c31e67fd1..d0d337918a15 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1818,4 +1818,41 @@ int remove_memory(int nid, u64 start, u64 size)
> return rc;
> }
> EXPORT_SYMBOL_GPL(remove_memory);
> +
> +/*
> + * Try to offline and remove a memory block. Might take a long time to
> + * finish in case memory is still in use. Primarily useful for memory devices
> + * that logically unplugged all memory (so it's no longer in use) and want to
> + * offline + remove the memory block.
> + */
> +int offline_and_remove_memory(int nid, u64 start, u64 size)
> +{
> + struct memory_block *mem;
> + int rc = -EINVAL;
> +
> + if (!IS_ALIGNED(start, memory_block_size_bytes()) ||
> + size != memory_block_size_bytes())
> + return rc;
> +
> + lock_device_hotplug();
> + mem = find_memory_block(__pfn_to_section(PFN_DOWN(start)));
> + if (mem)
> + rc = device_offline(&mem->dev);
> + /* Ignore if the device is already offline. */
> + if (rc > 0)
> + rc = 0;
> +
> + /*
> + * In case we succeeded to offline the memory block, remove it.
> + * This cannot fail as it cannot get onlined in the meantime.
> + */
> + if (!rc) {
> + rc = try_remove_memory(nid, start, size);
> + WARN_ON_ONCE(rc);
> + }
> + unlock_device_hotplug();
> +
> + return rc;
> +}
> +EXPORT_SYMBOL_GPL(offline_and_remove_memory);
> #endif /* CONFIG_MEMORY_HOTREMOVE */

Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>

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