mm/memory_hotplug: extend offline_and_remove_memory() to handle more than one memory...

virtio-mem soon wants to use offline_and_remove_memory() memory that
exceeds a single Linux memory block (memory_block_size_bytes()). Let's
remove that restriction.

Let's remember the old state and try to restore that if anything goes
wrong. While re-onlining can, in general, fail, it's highly unlikely to
happen (usually only when a notifier fails to allocate memory, and these
are rather rare).

This will be used by virtio-mem to offline+remove memory ranges that are
bigger than a single memory block - for example, with a device block
size of 1 GiB (e.g., gigantic pages in the hypervisor) and a Linux memory
block size of 128MB.

While we could compress the state into 2 bit, using 8 bit is much
easier.

This handling is similar, but different to acpi_scan_try_to_offline():

a) We don't try to offline twice. I am not sure if this CONFIG_MEMCG
optimization is still relevant - it should only apply to ZONE_NORMAL
(where we have no guarantees). If relevant, we can always add it.

b) acpi_scan_try_to_offline() simply onlines all memory in case
something goes wrong. It doesn't restore previous online type. Let's do
that, so we won't overwrite what e.g., user space configured.

Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20201112133815.13332-28-david@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 63b2e46..2b6cc42 100644 (file)
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1788,39 +1788,112 @@ int remove_memory(int nid, u64 start, u64 size)
 }
 EXPORT_SYMBOL_GPL(remove_memory);
 
 }
 EXPORT_SYMBOL_GPL(remove_memory);
 

+static int try_offline_memory_block(struct memory_block *mem, void *arg)
+{
+       uint8_t online_type = MMOP_ONLINE_KERNEL;
+       uint8_t **online_types = arg;
+       struct page *page;
+       int rc;
+
+       /*
+        * Sense the online_type via the zone of the memory block. Offlining
+        * with multiple zones within one memory block will be rejected
+        * by offlining code ... so we don't care about that.
+        */
+       page = pfn_to_online_page(section_nr_to_pfn(mem->start_section_nr));
+       if (page && zone_idx(page_zone(page)) == ZONE_MOVABLE)
+               online_type = MMOP_ONLINE_MOVABLE;
+
+       rc = device_offline(&mem->dev);
+       /*
+        * Default is MMOP_OFFLINE - change it only if offlining succeeded,
+        * so try_reonline_memory_block() can do the right thing.
+        */
+       if (!rc)
+               **online_types = online_type;
+
+       (*online_types)++;
+       /* Ignore if already offline. */
+       return rc < 0 ? rc : 0;
+}
+
+static int try_reonline_memory_block(struct memory_block *mem, void *arg)
+{
+       uint8_t **online_types = arg;
+       int rc;
+
+       if (**online_types != MMOP_OFFLINE) {
+               mem->online_type = **online_types;
+               rc = device_online(&mem->dev);
+               if (rc < 0)
+                       pr_warn("%s: Failed to re-online memory: %d",
+                               __func__, rc);
+       }
+
+       /* Continue processing all remaining memory blocks. */
+       (*online_types)++;
+       return 0;
+}
+

 /*
 /*

- * 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.
+ * Try to offline and remove memory. 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
+ * that memory.

  */
 int offline_and_remove_memory(int nid, u64 start, u64 size)
 {
  */
 int offline_and_remove_memory(int nid, u64 start, u64 size)
 {

-       struct memory_block *mem;
-       int rc = -EINVAL;
+       const unsigned long mb_count = size / memory_block_size_bytes();
+       uint8_t *online_types, *tmp;
+       int rc;

 
        if (!IS_ALIGNED(start, memory_block_size_bytes()) ||
 
        if (!IS_ALIGNED(start, memory_block_size_bytes()) ||

-           size != memory_block_size_bytes())
-               return rc;
+           !IS_ALIGNED(size, memory_block_size_bytes()) || !size)
+               return -EINVAL;
+
+       /*
+        * We'll remember the old online type of each memory block, so we can
+        * try to revert whatever we did when offlining one memory block fails
+        * after offlining some others succeeded.
+        */
+       online_types = kmalloc_array(mb_count, sizeof(*online_types),
+                                    GFP_KERNEL);
+       if (!online_types)
+               return -ENOMEM;
+       /*
+        * Initialize all states to MMOP_OFFLINE, so when we abort processing in
+        * try_offline_memory_block(), we'll skip all unprocessed blocks in
+        * try_reonline_memory_block().
+        */
+       memset(online_types, MMOP_OFFLINE, mb_count);

 
        lock_device_hotplug();
 
        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;
+
+       tmp = online_types;
+       rc = walk_memory_blocks(start, size, &tmp, try_offline_memory_block);

 
        /*
 
        /*

-        * In case we succeeded to offline the memory block, remove it.
+        * In case we succeeded to offline all memory, remove it.

         * This cannot fail as it cannot get onlined in the meantime.
         */
        if (!rc) {
                rc = try_remove_memory(nid, start, size);
         * This cannot fail as it cannot get onlined in the meantime.
         */
        if (!rc) {
                rc = try_remove_memory(nid, start, size);

-               WARN_ON_ONCE(rc);
+               if (rc)
+                       pr_err("%s: Failed to remove memory: %d", __func__, rc);
+       }
+
+       /*
+        * Rollback what we did. While memory onlining might theoretically fail
+        * (nacked by a notifier), it barely ever happens.
+        */
+       if (rc) {
+               tmp = online_types;
+               walk_memory_blocks(start, size, &tmp,
+                                  try_reonline_memory_block);

        }
        unlock_device_hotplug();
 
        }
        unlock_device_hotplug();
 

+       kfree(online_types);

        return rc;
 }
 EXPORT_SYMBOL_GPL(offline_and_remove_memory);
        return rc;
 }
 EXPORT_SYMBOL_GPL(offline_and_remove_memory);