Commit 269ac938 authored by David Hildenbrand's avatar David Hildenbrand Committed by Michael S. Tsirkin
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virtio-mem: Big Block Mode (BBM) - basic memory hotunplug 



Let's try to unplug completely offline big blocks first. Then, (if
enabled via unplug_offline) try to offline and remove whole big blocks.

No locking necessary - we can deal with concurrent onlining/offlining
just fine.

Note1: This is sub-optimal and might be dangerous in some environments: we
could end up in an infinite loop when offlining (e.g., long-term pinnings),
similar as with DIMMs. We'll introduce safe memory hotunplug via
fake-offlining next, and use this basic mode only when explicitly enabled.

Note2: Without ZONE_MOVABLE, memory unplug will be extremely unreliable
with bigger block sizes.

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: default avatarDavid Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20201112133815.13332-29-david@redhat.com


Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 8dc4bb58

drivers/virtio/virtio_mem.c

+155 −1
Original line number Diff line number Diff line
@@ -390,6 +390,12 @@ static int virtio_mem_bbm_bb_states_prepare_next_bb(struct virtio_mem *vm) 
	     _bb_id++) \

		if (virtio_mem_bbm_get_bb_state(_vm, _bb_id) == _state)



#define virtio_mem_bbm_for_each_bb_rev(_vm, _bb_id, _state) \

	for (_bb_id = vm->bbm.next_bb_id - 1; \

	     _bb_id >= vm->bbm.first_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.

 */
@@ -685,6 +691,18 @@ static int virtio_mem_sbm_remove_mb(struct virtio_mem *vm, unsigned long mb_id) 
	return virtio_mem_remove_memory(vm, addr, size);

}



/*

 * See virtio_mem_remove_memory(): Try to remove all Linux memory blocks covered

 * by the big block.

 */

static int virtio_mem_bbm_remove_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_remove_memory(vm, addr, size);

}



/*

 * Try offlining and removing memory from Linux.

 *
@@ -731,6 +749,19 @@ static int virtio_mem_sbm_offline_and_remove_mb(struct virtio_mem *vm, 
	return virtio_mem_offline_and_remove_memory(vm, addr, size);

}



/*

 * See virtio_mem_offline_and_remove_memory(): Try to offline and remove a

 * all Linux memory blocks covered by the big block.

 */

static int virtio_mem_bbm_offline_and_remove_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_offline_and_remove_memory(vm, addr, size);

}



/*

 * Trigger the workqueue so the device can perform its magic.

 */
@@ -1928,6 +1959,129 @@ static int virtio_mem_sbm_unplug_request(struct virtio_mem *vm, uint64_t diff) 
	return rc;

}



/*

 * Try to offline and remove a big block from Linux and unplug it. Will fail

 * with -EBUSY if some memory is busy and cannot get unplugged.

 *

 * Will modify the state of the memory block. Might temporarily drop the

 * hotplug_mutex.

 */

static int virtio_mem_bbm_offline_remove_and_unplug_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_ADDED))

		return -EINVAL;



	rc = virtio_mem_bbm_offline_and_remove_bb(vm, bb_id);

	if (rc)

		return rc;



	rc = virtio_mem_bbm_unplug_bb(vm, bb_id);

	if (rc)

		virtio_mem_bbm_set_bb_state(vm, bb_id,

					    VIRTIO_MEM_BBM_BB_PLUGGED);

	else

		virtio_mem_bbm_set_bb_state(vm, bb_id,

					    VIRTIO_MEM_BBM_BB_UNUSED);

	return rc;

}



/*

 * Try to remove a big block from Linux and unplug it. Will fail with

 * -EBUSY if some memory is online.

 *

 * Will modify the state of the memory block.

 */

static int virtio_mem_bbm_remove_and_unplug_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_ADDED))

		return -EINVAL;



	rc = virtio_mem_bbm_remove_bb(vm, bb_id);

	if (rc)

		return -EBUSY;



	rc = virtio_mem_bbm_unplug_bb(vm, bb_id);

	if (rc)

		virtio_mem_bbm_set_bb_state(vm, bb_id,

					    VIRTIO_MEM_BBM_BB_PLUGGED);

	else

		virtio_mem_bbm_set_bb_state(vm, bb_id,

					    VIRTIO_MEM_BBM_BB_UNUSED);

	return rc;

}



/*

 * Test if a big block is completely offline.

 */

static bool virtio_mem_bbm_bb_is_offline(struct virtio_mem *vm,

					 unsigned long bb_id)

{

	const unsigned long start_pfn = PFN_DOWN(virtio_mem_bb_id_to_phys(vm, bb_id));

	const unsigned long nr_pages = PFN_DOWN(vm->bbm.bb_size);

	unsigned long pfn;



	for (pfn = start_pfn; pfn < start_pfn + nr_pages;

	     pfn += PAGES_PER_SECTION) {

		if (pfn_to_online_page(pfn))

			return false;

	}



	return true;

}



static int virtio_mem_bbm_unplug_request(struct virtio_mem *vm, uint64_t diff)

{

	uint64_t nb_bb = diff / vm->bbm.bb_size;

	uint64_t bb_id;

	int rc;



	if (!nb_bb)

		return 0;



	/* Try to unplug completely offline big blocks first. */

	virtio_mem_bbm_for_each_bb_rev(vm, bb_id, VIRTIO_MEM_BBM_BB_ADDED) {

		cond_resched();

		/*

		 * As we're holding no locks, this check is racy as memory

		 * can get onlined in the meantime - but we'll fail gracefully.

		 */

		if (!virtio_mem_bbm_bb_is_offline(vm, bb_id))

			continue;

		rc = virtio_mem_bbm_remove_and_unplug_bb(vm, bb_id);

		if (rc == -EBUSY)

			continue;

		if (!rc)

			nb_bb--;

		if (rc || !nb_bb)

			return rc;

	}



	if (!unplug_online)

		return 0;



	/* Try to unplug any big blocks. */

	virtio_mem_bbm_for_each_bb_rev(vm, bb_id, VIRTIO_MEM_BBM_BB_ADDED) {

		cond_resched();

		rc = virtio_mem_bbm_offline_remove_and_unplug_bb(vm, bb_id);

		if (rc == -EBUSY)

			continue;

		if (!rc)

			nb_bb--;

		if (rc || !nb_bb)

			return rc;

	}



	return nb_bb ? -EBUSY : 0;

}



/*

 * Try to unplug the requested amount of memory.

 */
@@ -1935,7 +2089,7 @@ 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;

	return virtio_mem_bbm_unplug_request(vm, diff);

}



/*