Re: [PATCH v1 25/29] virtio-mem: Big Block Mode (BBM) memory hotplug

[Wei Yang]

On Mon, Oct 12, 2020 at 02:53:19PM +0200, David Hildenbrand wrote:
>Currently, we do not support device block sizes that exceed the Linux
>memory block size. For example, having a device block size of 1 GiB (e.g.,
>gigantic pages in the hypervisor) won't work with 128 MiB Linux memory
>blocks.
>
>Let's implement Big Block Mode (BBM), whereby we add/remove at least
>one Linux memory block at a time. With a 1 GiB device block size, a Big
>Block (BB) will cover 8 Linux memory blocks.
>
>We'll keep registering the online_page_callback machinery, it will be used
>for safe memory hotunplug in BBM next.
>
>Note: BBM is properly prepared for variable-sized Linux memory
>blocks that we might see in the future. So we won't care how many Linux
>memory blocks a big block actually spans, and how the memory notifier is
>called.
>
>Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
>Cc: Jason Wang <jasowang@xxxxxxxxxx>
>Cc: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx>
>Cc: Michal Hocko <mhocko@xxxxxxxxxx>
>Cc: Oscar Salvador <osalvador@xxxxxxx>
>Cc: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx>
>Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
>---
> drivers/virtio/virtio_mem.c | 484 ++++++++++++++++++++++++++++++------
> 1 file changed, 402 insertions(+), 82 deletions(-)
>
>diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
>index e68d0d99590c..4d396ef98a92 100644
>--- a/drivers/virtio/virtio_mem.c
>+++ b/drivers/virtio/virtio_mem.c
>@@ -30,12 +30,18 @@ MODULE_PARM_DESC(unplug_online, "Try to unplug online memory");
> /*
>  * virtio-mem currently supports the following modes of operation:
>  *
>- * * Sub Block Mode (SBM): A Linux memory block spans 1..X subblocks (SB). The
>+ * * Sub Block Mode (SBM): A Linux memory block spans 2..X subblocks (SB). The
>  *   size of a Sub Block (SB) is determined based on the device block size, the
>  *   pageblock size, and the maximum allocation granularity of the buddy.
>  *   Subblocks within a Linux memory block might either be plugged or unplugged.
>  *   Memory is added/removed to Linux MM in Linux memory block granularity.
>  *
>+ * * Big Block Mode (BBM): A Big Block (BB) spans 1..X Linux memory blocks.
>+ *   Memory is added/removed to Linux MM in Big Block granularity.
>+ *
>+ * The mode is determined automatically based on the Linux memory block size
>+ * and the device block size.
>+ *
>  * User space / core MM (auto onlining) is responsible for onlining added
>  * Linux memory blocks - and for selecting a zone. Linux Memory Blocks are
>  * always onlined separately, and all memory within a Linux memory block is
>@@ -61,6 +67,19 @@ enum virtio_mem_sbm_mb_state {
> 	VIRTIO_MEM_SBM_MB_COUNT
> };
> 
>+/*
>+ * State of a Big Block (BB) in BBM, covering 1..X Linux memory blocks.
>+ */
>+enum virtio_mem_bbm_bb_state {
>+	/* Unplugged, not added to Linux. Can be reused later. */
>+	VIRTIO_MEM_BBM_BB_UNUSED = 0,
>+	/* Plugged, not added to Linux. Error on add_memory(). */
>+	VIRTIO_MEM_BBM_BB_PLUGGED,
>+	/* Plugged and added to Linux. */
>+	VIRTIO_MEM_BBM_BB_ADDED,
>+	VIRTIO_MEM_BBM_BB_COUNT
>+};
>+
> struct virtio_mem {
> 	struct virtio_device *vdev;
> 
>@@ -113,6 +132,9 @@ struct virtio_mem {
> 	atomic64_t offline_size;
> 	uint64_t offline_threshold;
> 
>+	/* If set, the driver is in SBM, otherwise in BBM. */
>+	bool in_sbm;
>+
> 	struct {
> 		/* Id of the first memory block of this device. */
> 		unsigned long first_mb_id;
>@@ -151,9 +173,27 @@ struct virtio_mem {
> 		unsigned long *sb_states;
> 	} sbm;
> 
>+	struct {
>+		/* Id of the first big block of this device. */
>+		unsigned long first_bb_id;
>+		/* Id of the last usable big block of this device. */
>+		unsigned long last_usable_bb_id;
>+		/* Id of the next device bock to prepare when needed. */
>+		unsigned long next_bb_id;
>+
>+		/* Summary of all big block states. */
>+		unsigned long bb_count[VIRTIO_MEM_BBM_BB_COUNT];
>+
>+		/* One byte state per big block. See sbm.mb_states. */
>+		uint8_t *bb_states;
>+
>+		/* The block size used for (un)plugged, adding/removing. */
>+		uint64_t bb_size;
>+	} bbm;
>+
> 	/*
>-	 * Mutex that protects the sbm.mb_count, sbm.mb_states, and
>-	 * sbm.sb_states.
>+	 * Mutex that protects the sbm.mb_count, sbm.mb_states,
>+	 * sbm.sb_states, bbm.bb_count, and bbm.bb_states
> 	 *
> 	 * When this lock is held the pointers can't change, ONLINE and
> 	 * OFFLINE blocks can't change the state and no subblocks will get
>@@ -247,6 +287,24 @@ static unsigned long virtio_mem_mb_id_to_phys(unsigned long mb_id)
> 	return mb_id * memory_block_size_bytes();
> }
> 
>+/*
>+ * Calculate the big block id of a given address.
>+ */
>+static unsigned long virtio_mem_phys_to_bb_id(struct virtio_mem *vm,
>+					      uint64_t addr)
>+{
>+	return addr / vm->bbm.bb_size;
>+}
>+
>+/*
>+ * Calculate the physical start address of a given big block id.
>+ */
>+static uint64_t virtio_mem_bb_id_to_phys(struct virtio_mem *vm,
>+					 unsigned long bb_id)
>+{
>+	return bb_id * vm->bbm.bb_size;
>+}
>+
> /*
>  * Calculate the subblock id of a given address.
>  */
>@@ -259,6 +317,67 @@ static unsigned long virtio_mem_phys_to_sb_id(struct virtio_mem *vm,
> 	return (addr - mb_addr) / vm->sbm.sb_size;
> }
> 
>+/*
>+ * Set the state of a big block, taking care of the state counter.
>+ */
>+static void virtio_mem_bbm_set_bb_state(struct virtio_mem *vm,
>+					unsigned long bb_id,
>+					enum virtio_mem_bbm_bb_state state)
>+{
>+	const unsigned long idx = bb_id - vm->bbm.first_bb_id;
>+	enum virtio_mem_bbm_bb_state old_state;
>+
>+	old_state = vm->bbm.bb_states[idx];
>+	vm->bbm.bb_states[idx] = state;
>+
>+	BUG_ON(vm->bbm.bb_count[old_state] == 0);
>+	vm->bbm.bb_count[old_state]--;
>+	vm->bbm.bb_count[state]++;
>+}
>+
>+/*
>+ * Get the state of a big block.
>+ */
>+static enum virtio_mem_bbm_bb_state virtio_mem_bbm_get_bb_state(struct virtio_mem *vm,
>+								unsigned long bb_id)
>+{
>+	return vm->bbm.bb_states[bb_id - vm->bbm.first_bb_id];
>+}
>+
>+/*
>+ * Prepare the big block state array for the next big block.
>+ */
>+static int virtio_mem_bbm_bb_states_prepare_next_bb(struct virtio_mem *vm)
>+{
>+	unsigned long old_bytes = vm->bbm.next_bb_id - vm->bbm.first_bb_id;
>+	unsigned long new_bytes = old_bytes + 1;
>+	int old_pages = PFN_UP(old_bytes);
>+	int new_pages = PFN_UP(new_bytes);
>+	uint8_t *new_array;
>+
>+	if (vm->bbm.bb_states && old_pages == new_pages)
>+		return 0;
>+
>+	new_array = vzalloc(new_pages * PAGE_SIZE);
>+	if (!new_array)
>+		return -ENOMEM;
>+
>+	mutex_lock(&vm->hotplug_mutex);
>+	if (vm->bbm.bb_states)
>+		memcpy(new_array, vm->bbm.bb_states, old_pages * PAGE_SIZE);
>+	vfree(vm->bbm.bb_states);
>+	vm->bbm.bb_states = new_array;
>+	mutex_unlock(&vm->hotplug_mutex);
>+
>+	return 0;
>+}
>+
>+#define virtio_mem_bbm_for_each_bb(_vm, _bb_id, _state) \
>+	for (_bb_id = vm->bbm.first_bb_id; \
>+	     _bb_id < vm->bbm.next_bb_id && _vm->bbm.bb_count[_state]; \
>+	     _bb_id++) \
>+		if (virtio_mem_bbm_get_bb_state(_vm, _bb_id) == _state)
>+
> /*
>  * Set the state of a memory block, taking care of the state counter.
>  */
>@@ -504,6 +623,17 @@ static int virtio_mem_sbm_add_mb(struct virtio_mem *vm, unsigned long mb_id)
> 	return virtio_mem_add_memory(vm, addr, size);
> }
> 
>+/*
>+ * See virtio_mem_add_memory(): Try adding a big block.
>+ */
>+static int virtio_mem_bbm_add_bb(struct virtio_mem *vm, unsigned long bb_id)
>+{
>+	const uint64_t addr = virtio_mem_bb_id_to_phys(vm, bb_id);
>+	const uint64_t size = vm->bbm.bb_size;
>+
>+	return virtio_mem_add_memory(vm, addr, size);
>+}
>+
> /*
>  * Try removing memory from Linux. Will only fail if memory blocks aren't
>  * offline.
>@@ -731,20 +861,33 @@ static int virtio_mem_memory_notifier_cb(struct notifier_block *nb,
> 	struct memory_notify *mhp = arg;
> 	const unsigned long start = PFN_PHYS(mhp->start_pfn);
> 	const unsigned long size = PFN_PHYS(mhp->nr_pages);
>-	const unsigned long mb_id = virtio_mem_phys_to_mb_id(start);
> 	int rc = NOTIFY_OK;
>+	unsigned long id;
> 
> 	if (!virtio_mem_overlaps_range(vm, start, size))
> 		return NOTIFY_DONE;
> 
>-	/*
>-	 * Memory is onlined/offlined in memory block granularity. We cannot
>-	 * cross virtio-mem device boundaries and memory block boundaries. Bail
>-	 * out if this ever changes.
>-	 */
>-	if (WARN_ON_ONCE(size != memory_block_size_bytes() ||
>-			 !IS_ALIGNED(start, memory_block_size_bytes())))
>-		return NOTIFY_BAD;
>+	if (vm->in_sbm) {
>+		id = virtio_mem_phys_to_mb_id(start);
>+		/*
>+		 * In SBM, we add memory in separate memory blocks - we expect
>+		 * it to be onlined/offlined in the same granularity. Bail out
>+		 * if this ever changes.
>+		 */
>+		if (WARN_ON_ONCE(size != memory_block_size_bytes() ||
>+				 !IS_ALIGNED(start, memory_block_size_bytes())))
>+			return NOTIFY_BAD;
>+	} else {
>+		id = virtio_mem_phys_to_bb_id(vm, start);
>+		/*
>+		 * In BBM, we only care about onlining/offlining happening
>+		 * within a single big block, we don't care about the
>+		 * actual granularity as we don't track individual Linux
>+		 * memory blocks.
>+		 */
>+		if (WARN_ON_ONCE(id != virtio_mem_phys_to_bb_id(vm, start + size - 1)))
>+			return NOTIFY_BAD;
>+	}
> 
> 	/*
> 	 * Avoid circular locking lockdep warnings. We lock the mutex
>@@ -763,7 +906,8 @@ static int virtio_mem_memory_notifier_cb(struct notifier_block *nb,
> 			break;
> 		}
> 		vm->hotplug_active = true;
>-		virtio_mem_sbm_notify_going_offline(vm, mb_id);
>+		if (vm->in_sbm)
>+			virtio_mem_sbm_notify_going_offline(vm, id);
> 		break;
> 	case MEM_GOING_ONLINE:
> 		mutex_lock(&vm->hotplug_mutex);
>@@ -773,10 +917,12 @@ static int virtio_mem_memory_notifier_cb(struct notifier_block *nb,
> 			break;
> 		}
> 		vm->hotplug_active = true;
>-		rc = virtio_mem_sbm_notify_going_online(vm, mb_id);
>+		if (vm->in_sbm)
>+			rc = virtio_mem_sbm_notify_going_online(vm, id);
> 		break;
> 	case MEM_OFFLINE:
>-		virtio_mem_sbm_notify_offline(vm, mb_id);
>+		if (vm->in_sbm)
>+			virtio_mem_sbm_notify_offline(vm, id);
> 
> 		atomic64_add(size, &vm->offline_size);
> 		/*
>@@ -790,7 +936,8 @@ static int virtio_mem_memory_notifier_cb(struct notifier_block *nb,
> 		mutex_unlock(&vm->hotplug_mutex);
> 		break;
> 	case MEM_ONLINE:
>-		virtio_mem_sbm_notify_online(vm, mb_id);
>+		if (vm->in_sbm)
>+			virtio_mem_sbm_notify_online(vm, id);
> 
> 		atomic64_sub(size, &vm->offline_size);
> 		/*
>@@ -809,7 +956,8 @@ static int virtio_mem_memory_notifier_cb(struct notifier_block *nb,
> 	case MEM_CANCEL_OFFLINE:
> 		if (!vm->hotplug_active)
> 			break;
>-		virtio_mem_sbm_notify_cancel_offline(vm, mb_id);
>+		if (vm->in_sbm)
>+			virtio_mem_sbm_notify_cancel_offline(vm, id);
> 		vm->hotplug_active = false;
> 		mutex_unlock(&vm->hotplug_mutex);
> 		break;
>@@ -980,27 +1128,29 @@ static void virtio_mem_fake_offline_cancel_offline(unsigned long pfn,
> static void virtio_mem_online_page_cb(struct page *page, unsigned int order)
> {
> 	const unsigned long addr = page_to_phys(page);
>-	const unsigned long mb_id = virtio_mem_phys_to_mb_id(addr);
>+	unsigned long id, sb_id;
> 	struct virtio_mem *vm;
>-	int sb_id;
>+	bool do_online;
> 
>-	/*
>-	 * We exploit here that subblocks have at least MAX_ORDER_NR_PAGES.
>-	 * size/alignment and that this callback is is called with such a
>-	 * size/alignment. So we cannot cross subblocks and therefore
>-	 * also not memory blocks.
>-	 */
> 	rcu_read_lock();
> 	list_for_each_entry_rcu(vm, &virtio_mem_devices, next) {
> 		if (!virtio_mem_contains_range(vm, addr, PFN_PHYS(1 << order)))
> 			continue;
> 
>-		sb_id = virtio_mem_phys_to_sb_id(vm, addr);
>-		/*
>-		 * If plugged, online the pages, otherwise, set them fake
>-		 * offline (PageOffline).
>-		 */
>-		if (virtio_mem_sbm_test_sb_plugged(vm, mb_id, sb_id, 1))
>+		if (vm->in_sbm) {
>+			/*
>+			 * We exploit here that subblocks have at least
>+			 * MAX_ORDER_NR_PAGES size/alignment - so we cannot
>+			 * cross subblocks within one call.
>+			 */
>+			id = virtio_mem_phys_to_mb_id(addr);
>+			sb_id = virtio_mem_phys_to_sb_id(vm, addr);
>+			do_online = virtio_mem_sbm_test_sb_plugged(vm, id,
>+								   sb_id, 1);
>+		} else {
>+			do_online = true;
>+		}
>+		if (do_online)
> 			generic_online_page(page, order);
> 		else
> 			virtio_mem_set_fake_offline(PFN_DOWN(addr), 1 << order,
>@@ -1180,6 +1330,32 @@ static int virtio_mem_sbm_unplug_sb(struct virtio_mem *vm, unsigned long mb_id,
> 	return rc;
> }
> 
>+/*
>+ * Request to unplug a big block.
>+ *
>+ * Will not modify the state of the big block.
>+ */
>+static int virtio_mem_bbm_unplug_bb(struct virtio_mem *vm, unsigned long bb_id)
>+{
>+	const uint64_t addr = virtio_mem_bb_id_to_phys(vm, bb_id);
>+	const uint64_t size = vm->bbm.bb_size;
>+
>+	return virtio_mem_send_unplug_request(vm, addr, size);
>+}
>+
>+/*
>+ * Request to plug a big block.
>+ *
>+ * Will not modify the state of the big block.
>+ */
>+static int virtio_mem_bbm_plug_bb(struct virtio_mem *vm, unsigned long bb_id)
>+{
>+	const uint64_t addr = virtio_mem_bb_id_to_phys(vm, bb_id);
>+	const uint64_t size = vm->bbm.bb_size;
>+
>+	return virtio_mem_send_plug_request(vm, addr, size);
>+}
>+
> /*
>  * Unplug the desired number of plugged subblocks of a offline or not-added
>  * memory block. Will fail if any subblock cannot get unplugged (instead of
>@@ -1365,10 +1541,7 @@ static int virtio_mem_sbm_plug_any_sb(struct virtio_mem *vm,
> 	return 0;
> }
> 
>-/*
>- * Try to plug the requested amount of memory.
>- */
>-static int virtio_mem_plug_request(struct virtio_mem *vm, uint64_t diff)
>+static int virtio_mem_sbm_plug_request(struct virtio_mem *vm, uint64_t diff)
> {
> 	uint64_t nb_sb = diff / vm->sbm.sb_size;
> 	unsigned long mb_id;
>@@ -1435,6 +1608,112 @@ static int virtio_mem_plug_request(struct virtio_mem *vm, uint64_t diff)
> 	return rc;
> }
> 
>+/*
>+ * Plug a big block and add it to Linux.
>+ *
>+ * Will modify the state of the big block.
>+ */
>+static int virtio_mem_bbm_plug_and_add_bb(struct virtio_mem *vm,
>+					  unsigned long bb_id)
>+{
>+	int rc;
>+
>+	if (WARN_ON_ONCE(virtio_mem_bbm_get_bb_state(vm, bb_id) !=
>+			 VIRTIO_MEM_BBM_BB_UNUSED))
>+		return -EINVAL;
>+
>+	rc = virtio_mem_bbm_plug_bb(vm, bb_id);
>+	if (rc)
>+		return rc;
>+	virtio_mem_bbm_set_bb_state(vm, bb_id, VIRTIO_MEM_BBM_BB_ADDED);
>+
>+	rc = virtio_mem_bbm_add_bb(vm, bb_id);
>+	if (rc) {
>+		if (!virtio_mem_bbm_unplug_bb(vm, bb_id))
>+			virtio_mem_bbm_set_bb_state(vm, bb_id,
>+						    VIRTIO_MEM_BBM_BB_UNUSED);
>+		else
>+			/* Retry from the main loop. */
>+			virtio_mem_bbm_set_bb_state(vm, bb_id,
>+						    VIRTIO_MEM_BBM_BB_PLUGGED);
>+		return rc;
>+	}
>+	return 0;
>+}
>+
>+/*
>+ * Prepare tracking data for the next big block.
>+ */
>+static int virtio_mem_bbm_prepare_next_bb(struct virtio_mem *vm,
>+					  unsigned long *bb_id)
>+{
>+	int rc;
>+
>+	if (vm->bbm.next_bb_id > vm->bbm.last_usable_bb_id)
>+		return -ENOSPC;
>+
>+	/* Resize the big block state array if required. */
>+	rc = virtio_mem_bbm_bb_states_prepare_next_bb(vm);
>+	if (rc)
>+		return rc;
>+
>+	vm->bbm.bb_count[VIRTIO_MEM_BBM_BB_UNUSED]++;
>+	*bb_id = vm->bbm.next_bb_id;
>+	vm->bbm.next_bb_id++;
>+	return 0;
>+}
>+
>+static int virtio_mem_bbm_plug_request(struct virtio_mem *vm, uint64_t diff)
>+{
>+	uint64_t nb_bb = diff / vm->bbm.bb_size;
>+	unsigned long bb_id;
>+	int rc;
>+
>+	if (!nb_bb)
>+		return 0;
>+
>+	/* Try to plug and add unused big blocks */
>+	virtio_mem_bbm_for_each_bb(vm, bb_id, VIRTIO_MEM_BBM_BB_UNUSED) {
>+		if (!virtio_mem_could_add_memory(vm, vm->bbm.bb_size))
>+			return -ENOSPC;
>+
>+		rc = virtio_mem_bbm_plug_and_add_bb(vm, bb_id);
>+		if (!rc)
>+			nb_bb--;
>+		if (rc || !nb_bb)
>+			return rc;
>+		cond_resched();
>+	}
>+
>+	/* Try to prepare, plug and add new big blocks */
>+	while (nb_bb) {
>+		if (!virtio_mem_could_add_memory(vm, vm->bbm.bb_size))
>+			return -ENOSPC;
>+
>+		rc = virtio_mem_bbm_prepare_next_bb(vm, &bb_id);
>+		if (rc)
>+			return rc;
>+		rc = virtio_mem_bbm_plug_and_add_bb(vm, bb_id);
>+		if (!rc)
>+			nb_bb--;
>+		if (rc)
>+			return rc;
>+		cond_resched();
>+	}
>+
>+	return 0;
>+}
>+
>+/*
>+ * Try to plug the requested amount of memory.
>+ */
>+static int virtio_mem_plug_request(struct virtio_mem *vm, uint64_t diff)
>+{
>+	if (vm->in_sbm)
>+		return virtio_mem_sbm_plug_request(vm, diff);
>+	return virtio_mem_bbm_plug_request(vm, diff);
>+}
>+
> /*
>  * Unplug the desired number of plugged subblocks of an offline memory block.
>  * Will fail if any subblock cannot get unplugged (instead of skipping it).
>@@ -1573,10 +1852,7 @@ static int virtio_mem_sbm_unplug_any_sb_online(struct virtio_mem *vm,
> 	return 0;
> }
> 
>-/*
>- * Try to unplug the requested amount of memory.
>- */
>-static int virtio_mem_unplug_request(struct virtio_mem *vm, uint64_t diff)
>+static int virtio_mem_sbm_unplug_request(struct virtio_mem *vm, uint64_t diff)
> {
> 	uint64_t nb_sb = diff / vm->sbm.sb_size;
> 	unsigned long mb_id;
>@@ -1642,20 +1918,42 @@ static int virtio_mem_unplug_request(struct virtio_mem *vm, uint64_t diff)
> 	return rc;
> }
> 
>+/*
>+ * Try to unplug the requested amount of memory.
>+ */
>+static int virtio_mem_unplug_request(struct virtio_mem *vm, uint64_t diff)
>+{
>+	if (vm->in_sbm)
>+		return virtio_mem_sbm_unplug_request(vm, diff);
>+	return -EBUSY;
>+}
>+
> /*
>  * Try to unplug all blocks that couldn't be unplugged before, for example,
>  * because the hypervisor was busy.
>  */
> static int virtio_mem_unplug_pending_mb(struct virtio_mem *vm)
> {
>-	unsigned long mb_id;
>+	unsigned long id;
> 	int rc;
> 
>-	virtio_mem_sbm_for_each_mb(vm, mb_id, VIRTIO_MEM_SBM_MB_PLUGGED) {
>-		rc = virtio_mem_sbm_unplug_mb(vm, mb_id);
>+	if (!vm->in_sbm) {
>+		virtio_mem_bbm_for_each_bb(vm, id,
>+					   VIRTIO_MEM_BBM_BB_PLUGGED) {
>+			rc = virtio_mem_bbm_unplug_bb(vm, id);
>+			if (rc)
>+				return rc;
>+			virtio_mem_bbm_set_bb_state(vm, id,
>+						    VIRTIO_MEM_BBM_BB_UNUSED);
>+		}
>+		return 0;
>+	}
>+
>+	virtio_mem_sbm_for_each_mb(vm, id, VIRTIO_MEM_SBM_MB_PLUGGED) {
>+		rc = virtio_mem_sbm_unplug_mb(vm, id);
> 		if (rc)
> 			return rc;
>-		virtio_mem_sbm_set_mb_state(vm, mb_id,
>+		virtio_mem_sbm_set_mb_state(vm, id,
> 					    VIRTIO_MEM_SBM_MB_UNUSED);
> 	}
> 
>@@ -1681,7 +1979,13 @@ static void virtio_mem_refresh_config(struct virtio_mem *vm)
> 			usable_region_size, &usable_region_size);
> 	end_addr = vm->addr + usable_region_size;
> 	end_addr = min(end_addr, phys_limit);
>-	vm->sbm.last_usable_mb_id = virtio_mem_phys_to_mb_id(end_addr) - 1;
>+
>+	if (vm->in_sbm)
>+		vm->sbm.last_usable_mb_id =
>+					 virtio_mem_phys_to_mb_id(end_addr) - 1;
>+	else
>+		vm->bbm.last_usable_bb_id =
>+				     virtio_mem_phys_to_bb_id(vm, end_addr) - 1;
> 
> 	/* see if there is a request to change the size */
> 	virtio_cread_le(vm->vdev, struct virtio_mem_config, requested_size,
>@@ -1804,6 +2108,7 @@ static int virtio_mem_init_vq(struct virtio_mem *vm)
> static int virtio_mem_init(struct virtio_mem *vm)
> {
> 	const uint64_t phys_limit = 1UL << MAX_PHYSMEM_BITS;
>+	uint64_t sb_size, addr;
> 	uint16_t node_id;
> 
> 	if (!vm->vdev->config->get) {
>@@ -1836,16 +2141,6 @@ static int virtio_mem_init(struct virtio_mem *vm)
> 	if (vm->nid == NUMA_NO_NODE)
> 		vm->nid = memory_add_physaddr_to_nid(vm->addr);
> 
>-	/*
>-	 * We always hotplug memory in memory block granularity. This way,
>-	 * we have to wait for exactly one memory block to online.
>-	 */
>-	if (vm->device_block_size > memory_block_size_bytes()) {
>-		dev_err(&vm->vdev->dev,
>-			"The block size is not supported (too big).\n");
>-		return -EINVAL;
>-	}
>-
> 	/* bad device setup - warn only */
> 	if (!IS_ALIGNED(vm->addr, memory_block_size_bytes()))
> 		dev_warn(&vm->vdev->dev,
>@@ -1865,20 +2160,35 @@ static int virtio_mem_init(struct virtio_mem *vm)
> 	 * - Is required for now for alloc_contig_range() to work reliably -
> 	 *   it doesn't properly handle smaller granularity on ZONE_NORMAL.
> 	 */
>-	vm->sbm.sb_size = max_t(uint64_t, MAX_ORDER_NR_PAGES,
>-				pageblock_nr_pages) * PAGE_SIZE;
>-	vm->sbm.sb_size = max_t(uint64_t, vm->device_block_size,
>-				vm->sbm.sb_size);
>-	vm->sbm.sbs_per_mb = memory_block_size_bytes() / vm->sbm.sb_size;
>+	sb_size = max_t(uint64_t, MAX_ORDER_NR_PAGES,
>+			pageblock_nr_pages) * PAGE_SIZE;
>+	sb_size = max_t(uint64_t, vm->device_block_size, sb_size);
>+
>+	if (sb_size < memory_block_size_bytes()) {
>+		/* SBM: At least two subblocks per Linux memory block. */
>+		vm->in_sbm = true;
>+		vm->sbm.sb_size = sb_size;
>+		vm->sbm.sbs_per_mb = memory_block_size_bytes() /
>+				     vm->sbm.sb_size;
>+
>+		/* Round up to the next full memory block */
>+		addr = vm->addr + memory_block_size_bytes() - 1;
>+		vm->sbm.first_mb_id = virtio_mem_phys_to_mb_id(addr);
>+		vm->sbm.next_mb_id = vm->sbm.first_mb_id;
>+	} else {
>+		/* BBM: At least one Linux memory block. */
>+		vm->bbm.bb_size = vm->device_block_size;
> 
>-	/* Round up to the next full memory block */
>-	vm->sbm.first_mb_id = virtio_mem_phys_to_mb_id(vm->addr - 1 +
>-						       memory_block_size_bytes());
>-	vm->sbm.next_mb_id = vm->sbm.first_mb_id;
>+		vm->bbm.first_bb_id = virtio_mem_phys_to_bb_id(vm, vm->addr);

Per my understanding, vm->addr is not guaranteed to be bb_size aligned, right?

Why not round up to next big block?

>+		vm->bbm.next_bb_id = vm->bbm.first_bb_id;
>+	}
> 
> 	/* Prepare the offline threshold - make sure we can add two blocks. */
> 	vm->offline_threshold = max_t(uint64_t, 2 * memory_block_size_bytes(),
> 				      VIRTIO_MEM_DEFAULT_OFFLINE_THRESHOLD);
>+	/* In BBM, we also want at least two big blocks. */
>+	vm->offline_threshold = max_t(uint64_t, 2 * vm->bbm.bb_size,
>+				      vm->offline_threshold);
> 
> 	dev_info(&vm->vdev->dev, "start address: 0x%llx", vm->addr);
> 	dev_info(&vm->vdev->dev, "region size: 0x%llx", vm->region_size);
>@@ -1886,8 +2196,12 @@ static int virtio_mem_init(struct virtio_mem *vm)
> 		 (unsigned long long)vm->device_block_size);
> 	dev_info(&vm->vdev->dev, "memory block size: 0x%lx",
> 		 memory_block_size_bytes());
>-	dev_info(&vm->vdev->dev, "subblock size: 0x%llx",
>-		 (unsigned long long)vm->sbm.sb_size);
>+	if (vm->in_sbm)
>+		dev_info(&vm->vdev->dev, "subblock size: 0x%llx",
>+			 (unsigned long long)vm->sbm.sb_size);
>+	else
>+		dev_info(&vm->vdev->dev, "big block size: 0x%llx",
>+			 (unsigned long long)vm->bbm.bb_size);
> 	if (vm->nid != NUMA_NO_NODE && IS_ENABLED(CONFIG_NUMA))
> 		dev_info(&vm->vdev->dev, "nid: %d", vm->nid);
> 
>@@ -2044,22 +2358,24 @@ static void virtio_mem_remove(struct virtio_device *vdev)
> 	cancel_work_sync(&vm->wq);
> 	hrtimer_cancel(&vm->retry_timer);
> 
>-	/*
>-	 * After we unregistered our callbacks, user space can online partially
>-	 * plugged offline blocks. Make sure to remove them.
>-	 */
>-	virtio_mem_sbm_for_each_mb(vm, mb_id,
>-				   VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL) {
>-		rc = virtio_mem_sbm_remove_mb(vm, mb_id);
>-		BUG_ON(rc);
>-		virtio_mem_sbm_set_mb_state(vm, mb_id,
>-					    VIRTIO_MEM_SBM_MB_UNUSED);
>+	if (vm->in_sbm) {
>+		/*
>+		 * After we unregistered our callbacks, user space can online
>+		 * partially plugged offline blocks. Make sure to remove them.
>+		 */
>+		virtio_mem_sbm_for_each_mb(vm, mb_id,
>+					   VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL) {
>+			rc = virtio_mem_sbm_remove_mb(vm, mb_id);
>+			BUG_ON(rc);
>+			virtio_mem_sbm_set_mb_state(vm, mb_id,
>+						    VIRTIO_MEM_SBM_MB_UNUSED);
>+		}
>+		/*
>+		 * After we unregistered our callbacks, user space can no longer
>+		 * offline partially plugged online memory blocks. No need to
>+		 * worry about them.
>+		 */
> 	}
>-	/*
>-	 * 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);
>@@ -2078,8 +2394,12 @@ static void virtio_mem_remove(struct virtio_device *vdev)
> 	}
> 
> 	/* remove all tracking data - no locking needed */
>-	vfree(vm->sbm.mb_states);
>-	vfree(vm->sbm.sb_states);
>+	if (vm->in_sbm) {
>+		vfree(vm->sbm.mb_states);
>+		vfree(vm->sbm.sb_states);
>+	} else {
>+		vfree(vm->bbm.bb_states);
>+	}
> 
> 	/* reset the device and cleanup the queues */
> 	vdev->config->reset(vdev);
>-- 
>2.26.2

-- 
Wei Yang
Help you, Help me