Commit c627ff5d authored by David Hildenbrand's avatar David Hildenbrand Committed by Michael S. Tsirkin
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virtio-mem: Paravirtualized memory hotunplug part 1 



Unplugging subblocks of memory blocks that are offline is easy. All we
have to do is watch out for concurrent onlining activity.

Tested-by: default avatarPankaj Gupta <pankaj.gupta.linux@gmail.com>
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: default avatarDavid Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20200507140139.17083-5-david@redhat.com


Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent f2af6d39

drivers/virtio/virtio_mem.c

+114 −2
Original line number Diff line number Diff line
@@ -123,7 +123,7 @@ struct virtio_mem { 
	 *

	 * When this lock is held the pointers can't change, ONLINE and

	 * OFFLINE blocks can't change the state and no subblocks will get

	 * plugged.

	 * plugged/unplugged.

	 */

	struct mutex hotplug_mutex;

	bool hotplug_active;
@@ -280,6 +280,12 @@ static int virtio_mem_mb_state_prepare_next_mb(struct virtio_mem *vm) 
	     _mb_id++) \

		if (virtio_mem_mb_get_state(_vm, _mb_id) == _state)



#define virtio_mem_for_each_mb_state_rev(_vm, _mb_id, _state) \

	for (_mb_id = _vm->next_mb_id - 1; \

	     _mb_id >= _vm->first_mb_id && _vm->nb_mb_state[_state]; \

	     _mb_id--) \

		if (virtio_mem_mb_get_state(_vm, _mb_id) == _state)



/*

 * Mark all selected subblocks plugged.

 *
@@ -325,6 +331,19 @@ static bool virtio_mem_mb_test_sb_plugged(struct virtio_mem *vm, 
	       bit + count;

}



/*

 * Test if all selected subblocks are unplugged.

 */

static bool virtio_mem_mb_test_sb_unplugged(struct virtio_mem *vm,

					    unsigned long mb_id, int sb_id,

					    int count)

{

	const int bit = (mb_id - vm->first_mb_id) * vm->nb_sb_per_mb + sb_id;



	/* TODO: Helper similar to bitmap_set() */

	return find_next_bit(vm->sb_bitmap, bit + count, bit) >= bit + count;

}



/*

 * Find the first plugged subblock. Returns vm->nb_sb_per_mb in case there is

 * none.
@@ -513,6 +532,9 @@ static void virtio_mem_notify_offline(struct virtio_mem *vm, 
		BUG();

		break;

	}



	/* trigger the workqueue, maybe we can now unplug memory. */

	virtio_mem_retry(vm);

}



static void virtio_mem_notify_online(struct virtio_mem *vm, unsigned long mb_id,
@@ -1122,6 +1144,94 @@ static int virtio_mem_plug_request(struct virtio_mem *vm, uint64_t diff) 
	return rc;

}



/*

 * Unplug the desired number of plugged subblocks of an offline memory block.

 * Will fail if any subblock cannot get unplugged (instead of skipping it).

 *

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

 * hotplug_mutex.

 *

 * Note: Can fail after some subblocks were successfully unplugged.

 */

static int virtio_mem_mb_unplug_any_sb_offline(struct virtio_mem *vm,

					       unsigned long mb_id,

					       uint64_t *nb_sb)

{

	int rc;



	rc = virtio_mem_mb_unplug_any_sb(vm, mb_id, nb_sb);



	/* some subblocks might have been unplugged even on failure */

	if (!virtio_mem_mb_test_sb_plugged(vm, mb_id, 0, vm->nb_sb_per_mb))

		virtio_mem_mb_set_state(vm, mb_id,

					VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL);

	if (rc)

		return rc;



	if (virtio_mem_mb_test_sb_unplugged(vm, mb_id, 0, vm->nb_sb_per_mb)) {

		/*

		 * Remove the block from Linux - this should never fail.

		 * Hinder the block from getting onlined by marking it

		 * unplugged. Temporarily drop the mutex, so

		 * any pending GOING_ONLINE requests can be serviced/rejected.

		 */

		virtio_mem_mb_set_state(vm, mb_id,

					VIRTIO_MEM_MB_STATE_UNUSED);



		mutex_unlock(&vm->hotplug_mutex);

		rc = virtio_mem_mb_remove(vm, mb_id);

		BUG_ON(rc);

		mutex_lock(&vm->hotplug_mutex);

	}

	return 0;

}



/*

 * Try to unplug the requested amount of memory.

 */

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

{

	uint64_t nb_sb = diff / vm->subblock_size;

	unsigned long mb_id;

	int rc;



	if (!nb_sb)

		return 0;



	/*

	 * We'll drop the mutex a couple of times when it is safe to do so.

	 * This might result in some blocks switching the state (online/offline)

	 * and we could miss them in this run - we will retry again later.

	 */

	mutex_lock(&vm->hotplug_mutex);



	/* Try to unplug subblocks of partially plugged offline blocks. */

	virtio_mem_for_each_mb_state_rev(vm, mb_id,

					 VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL) {

		rc = virtio_mem_mb_unplug_any_sb_offline(vm, mb_id,

							 &nb_sb);

		if (rc || !nb_sb)

			goto out_unlock;

		cond_resched();

	}



	/* Try to unplug subblocks of plugged offline blocks. */

	virtio_mem_for_each_mb_state_rev(vm, mb_id,

					 VIRTIO_MEM_MB_STATE_OFFLINE) {

		rc = virtio_mem_mb_unplug_any_sb_offline(vm, mb_id,

							 &nb_sb);

		if (rc || !nb_sb)

			goto out_unlock;

		cond_resched();

	}



	mutex_unlock(&vm->hotplug_mutex);

	return 0;

out_unlock:

	mutex_unlock(&vm->hotplug_mutex);

	return rc;

}



/*

 * Try to unplug all blocks that couldn't be unplugged before, for example,

 * because the hypervisor was busy.
@@ -1204,8 +1314,10 @@ static void virtio_mem_run_wq(struct work_struct *work) 
		if (vm->requested_size > vm->plugged_size) {

			diff = vm->requested_size - vm->plugged_size;

			rc = virtio_mem_plug_request(vm, diff);

		} else {

			diff = vm->plugged_size - vm->requested_size;

			rc = virtio_mem_unplug_request(vm, diff);

		}

		/* TODO: try to unplug memory */

	}



	switch (rc) {