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Subject[PATCH RFC v4 08/13] mm/memory_hotplug: Introduce offline_and_remove_memory()
Date
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.

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 | 35 ++++++++++++++++++++++++++++++++++
2 files changed, 36 insertions(+)

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index ba0dca6aac6e..586f5c59c291 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -310,6 +310,7 @@ 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 da01453a04e6..d04369e6d3cc 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1825,4 +1825,39 @@ 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 && try_remove_memory(nid, start, size))
+ BUG();
+ unlock_device_hotplug();
+
+ return rc;
+}
+EXPORT_SYMBOL_GPL(offline_and_remove_memory);
#endif /* CONFIG_MEMORY_HOTREMOVE */
--
2.23.0
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