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Subject[PATCH RFC v4 07/13] virtio-mem: Allow to offline partially unplugged memory blocks
Date
Dropping the reference count of PageOffline() pages allows offlining
code to skip them. However, we also have to convert PG_reserved to
another flag - let's use PG_dirty - so has_unmovable_pages() will
properly handle them. PG_reserved pages get detected as unmovable right
away.

We need the flag to see if we are onlining pages the first time, or if
we allocated them via alloc_contig_range().

Properly take care of offlining code also modifying the stats and
special handling in case the driver gets unloaded.

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
drivers/virtio/virtio_mem.c | 64 ++++++++++++++++++++++++++++++++++++-
1 file changed, 63 insertions(+), 1 deletion(-)

diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index 5a142a371222..a12a0f9c076b 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -564,6 +564,53 @@ static void virtio_mem_notify_online(struct virtio_mem *vm, unsigned long mb_id,
virtio_mem_retry(vm);
}

+static void virtio_mem_notify_going_offline(struct virtio_mem *vm,
+ unsigned long mb_id)
+{
+ const unsigned long nr_pages = PFN_DOWN(vm->subblock_size);
+ unsigned long pfn;
+ int sb_id, i;
+
+ for (sb_id = 0; sb_id < vm->nb_sb_per_mb; sb_id++) {
+ if (virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id, 1))
+ continue;
+ /*
+ * Drop our reference to the pages so the memory can get
+ * offlined and add the unplugged pages to the managed
+ * page counters (so offlining code can correctly subtract
+ * them again).
+ */
+ pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
+ sb_id * vm->subblock_size);
+ adjust_managed_page_count(pfn_to_page(pfn), nr_pages);
+ for (i = 0; i < nr_pages; i++)
+ page_ref_dec(pfn_to_page(pfn + i));
+ }
+}
+
+static void virtio_mem_notify_cancel_offline(struct virtio_mem *vm,
+ unsigned long mb_id)
+{
+ const unsigned long nr_pages = PFN_DOWN(vm->subblock_size);
+ unsigned long pfn;
+ int sb_id, i;
+
+ for (sb_id = 0; sb_id < vm->nb_sb_per_mb; sb_id++) {
+ if (virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id, 1))
+ continue;
+ /*
+ * Get the reference we dropped when going offline and
+ * subtract the unplugged pages from the managed page
+ * counters.
+ */
+ pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
+ sb_id * vm->subblock_size);
+ adjust_managed_page_count(pfn_to_page(pfn), -nr_pages);
+ for (i = 0; i < nr_pages; i++)
+ page_ref_inc(pfn_to_page(pfn + i));
+ }
+}
+
/*
* This callback will either be called synchonously from add_memory() or
* asynchronously (e.g., triggered via user space). We have to be careful
@@ -611,6 +658,7 @@ static int virtio_mem_memory_notifier_cb(struct notifier_block *nb,
break;
mutex_lock(&vm->hotplug_mutex);
vm->hotplug_active = true;
+ virtio_mem_notify_going_offline(vm, mb_id);
break;
case MEM_GOING_ONLINE:
spin_lock_irq(&vm->removal_lock);
@@ -636,6 +684,12 @@ static int virtio_mem_memory_notifier_cb(struct notifier_block *nb,
mutex_unlock(&vm->hotplug_mutex);
break;
case MEM_CANCEL_OFFLINE:
+ if (!vm->hotplug_active)
+ break;
+ virtio_mem_notify_cancel_offline(vm, mb_id);
+ vm->hotplug_active = false;
+ mutex_unlock(&vm->hotplug_mutex);
+ break;
case MEM_CANCEL_ONLINE:
if (!vm->hotplug_active)
break;
@@ -660,8 +714,11 @@ static void virtio_mem_set_fake_offline(unsigned long pfn,
struct page *page = pfn_to_page(pfn);

__SetPageOffline(page);
- if (!onlined)
+ if (!onlined) {
SetPageDirty(page);
+ /* FIXME: remove after cleanups */
+ ClearPageReserved(page);
+ }
}
}

@@ -1719,6 +1776,11 @@ static void virtio_mem_remove(struct virtio_device *vdev)
rc = virtio_mem_mb_remove(vm, mb_id);
BUG_ON(rc);
}
+ /*
+ * After we unregistered our callbacks, user space can no longer
+ * offline partially plugged online memory blocks. No need to worry
+ * about them.
+ */

/* unregister callbacks */
unregister_virtio_mem_device(vm);
--
2.23.0
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