From fad7b7b27b6a168ca8ebc84482043886f837b89d Mon Sep 17 00:00:00 2001 From: Petr Mladek Date: Mon, 25 Jan 2016 17:38:05 +0100 Subject: virtio_balloon: Use a workqueue instead of "vballoon" kthread This patch moves the deferred work from the "vballoon" kthread into a system freezable workqueue. We do not need to maintain and run a dedicated kthread. Also the event driven workqueues API makes the logic much easier. Especially, we do not longer need an own wait queue, wait function, and freeze point. The conversion is pretty straightforward. One cycle of the main loop is put into a work. The work is queued instead of waking the kthread. fill_balloon() and leak_balloon() have a limit for the amount of modified pages. The work re-queues itself when necessary. For this, we make fill_balloon() to return the number of really modified pages. Note that leak_balloon() already did this. virtballoon_restore() queues the work only when really needed. The only complication is that we need to prevent queuing the work when the balloon is being removed. It was easier before because the kthread simply removed itself from the wait queue. We need an extra boolean and spin lock now. My initial idea was to use a dedicated workqueue. Michael S. Tsirkin suggested using a system one. Tejun Heo confirmed that the system workqueue has a pretty high concurrency level (256) by default. Therefore we need not be afraid of too long blocking. Signed-off-by: Petr Mladek Signed-off-by: Michael S. Tsirkin --- drivers/virtio/virtio_balloon.c | 108 +++++++++++++++++++--------------------- 1 file changed, 51 insertions(+), 57 deletions(-) (limited to 'drivers/virtio/virtio_balloon.c') diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index 0c3691f46575..2c9a92f1e525 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -22,8 +22,7 @@ #include #include #include -#include -#include +#include #include #include #include @@ -49,11 +48,12 @@ struct virtio_balloon { struct virtio_device *vdev; struct virtqueue *inflate_vq, *deflate_vq, *stats_vq; - /* Where the ballooning thread waits for config to change. */ - wait_queue_head_t config_change; + /* The balloon servicing is delegated to a freezable workqueue. */ + struct work_struct work; - /* The thread servicing the balloon. */ - struct task_struct *thread; + /* Prevent updating balloon when it is being canceled. */ + spinlock_t stop_update_lock; + bool stop_update; /* Waiting for host to ack the pages we released. */ wait_queue_head_t acked; @@ -135,9 +135,10 @@ static void set_page_pfns(u32 pfns[], struct page *page) pfns[i] = page_to_balloon_pfn(page) + i; } -static void fill_balloon(struct virtio_balloon *vb, size_t num) +static unsigned fill_balloon(struct virtio_balloon *vb, size_t num) { struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info; + unsigned num_allocated_pages; /* We can only do one array worth at a time. */ num = min(num, ARRAY_SIZE(vb->pfns)); @@ -162,10 +163,13 @@ static void fill_balloon(struct virtio_balloon *vb, size_t num) adjust_managed_page_count(page, -1); } + num_allocated_pages = vb->num_pfns; /* Did we get any? */ if (vb->num_pfns != 0) tell_host(vb, vb->inflate_vq); mutex_unlock(&vb->balloon_lock); + + return num_allocated_pages; } static void release_pages_balloon(struct virtio_balloon *vb) @@ -251,14 +255,19 @@ static void update_balloon_stats(struct virtio_balloon *vb) * with a single buffer. From that point forward, all conversations consist of * a hypervisor request (a call to this function) which directs us to refill * the virtqueue with a fresh stats buffer. Since stats collection can sleep, - * we notify our kthread which does the actual work via stats_handle_request(). + * we delegate the job to a freezable workqueue that will do the actual work via + * stats_handle_request(). */ static void stats_request(struct virtqueue *vq) { struct virtio_balloon *vb = vq->vdev->priv; vb->need_stats_update = 1; - wake_up(&vb->config_change); + + spin_lock(&vb->stop_update_lock); + if (!vb->stop_update) + queue_work(system_freezable_wq, &vb->work); + spin_unlock(&vb->stop_update_lock); } static void stats_handle_request(struct virtio_balloon *vb) @@ -281,8 +290,12 @@ static void stats_handle_request(struct virtio_balloon *vb) static void virtballoon_changed(struct virtio_device *vdev) { struct virtio_balloon *vb = vdev->priv; + unsigned long flags; - wake_up(&vb->config_change); + spin_lock_irqsave(&vb->stop_update_lock, flags); + if (!vb->stop_update) + queue_work(system_freezable_wq, &vb->work); + spin_unlock_irqrestore(&vb->stop_update_lock, flags); } static inline s64 towards_target(struct virtio_balloon *vb) @@ -345,43 +358,25 @@ static int virtballoon_oom_notify(struct notifier_block *self, return NOTIFY_OK; } -static int balloon(void *_vballoon) +static void balloon(struct work_struct *work) { - struct virtio_balloon *vb = _vballoon; - DEFINE_WAIT_FUNC(wait, woken_wake_function); - - set_freezable(); - while (!kthread_should_stop()) { - s64 diff; - - try_to_freeze(); - - add_wait_queue(&vb->config_change, &wait); - for (;;) { - if ((diff = towards_target(vb)) != 0 || - vb->need_stats_update || - kthread_should_stop() || - freezing(current)) - break; - wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT); - } - remove_wait_queue(&vb->config_change, &wait); + struct virtio_balloon *vb; + s64 diff; - if (vb->need_stats_update) - stats_handle_request(vb); - if (diff > 0) - fill_balloon(vb, diff); - else if (diff < 0) - leak_balloon(vb, -diff); - update_balloon_size(vb); + vb = container_of(work, struct virtio_balloon, work); + diff = towards_target(vb); - /* - * For large balloon changes, we could spend a lot of time - * and always have work to do. Be nice if preempt disabled. - */ - cond_resched(); - } - return 0; + if (vb->need_stats_update) + stats_handle_request(vb); + + if (diff > 0) + diff -= fill_balloon(vb, diff); + else if (diff < 0) + diff += leak_balloon(vb, -diff); + update_balloon_size(vb); + + if (diff) + queue_work(system_freezable_wq, work); } static int init_vqs(struct virtio_balloon *vb) @@ -499,9 +494,11 @@ static int virtballoon_probe(struct virtio_device *vdev) goto out; } + INIT_WORK(&vb->work, balloon); + spin_lock_init(&vb->stop_update_lock); + vb->stop_update = false; vb->num_pages = 0; mutex_init(&vb->balloon_lock); - init_waitqueue_head(&vb->config_change); init_waitqueue_head(&vb->acked); vb->vdev = vdev; vb->need_stats_update = 0; @@ -523,16 +520,8 @@ static int virtballoon_probe(struct virtio_device *vdev) virtio_device_ready(vdev); - vb->thread = kthread_run(balloon, vb, "vballoon"); - if (IS_ERR(vb->thread)) { - err = PTR_ERR(vb->thread); - goto out_del_vqs; - } - return 0; -out_del_vqs: - unregister_oom_notifier(&vb->nb); out_oom_notify: vdev->config->del_vqs(vdev); out_free_vb: @@ -559,7 +548,12 @@ static void virtballoon_remove(struct virtio_device *vdev) struct virtio_balloon *vb = vdev->priv; unregister_oom_notifier(&vb->nb); - kthread_stop(vb->thread); + + spin_lock_irq(&vb->stop_update_lock); + vb->stop_update = true; + spin_unlock_irq(&vb->stop_update_lock); + cancel_work_sync(&vb->work); + remove_common(vb); kfree(vb); } @@ -570,10 +564,9 @@ static int virtballoon_freeze(struct virtio_device *vdev) struct virtio_balloon *vb = vdev->priv; /* - * The kthread is already frozen by the PM core before this + * The workqueue is already frozen by the PM core before this * function is called. */ - remove_common(vb); return 0; } @@ -589,7 +582,8 @@ static int virtballoon_restore(struct virtio_device *vdev) virtio_device_ready(vdev); - fill_balloon(vb, towards_target(vb)); + if (towards_target(vb)) + virtballoon_changed(vdev); update_balloon_size(vb); return 0; } -- cgit v1.2.3-59-g8ed1b From fd0e21c31e1e6383af978239d07ced6e4e5d82c3 Mon Sep 17 00:00:00 2001 From: Petr Mladek Date: Mon, 25 Jan 2016 17:38:06 +0100 Subject: virtio_balloon: Allow to resize and update the balloon stats in parallel The virtio balloon statistics are not updated when the balloon is being resized. But it seems that both tasks could be done in parallel. stats_handle_request() updates the statistics in the balloon structure and then communicates with the host. update_balloon_stats() calls all_vm_events() that just reads some per-CPU variables. The values might change during and after the call but it is expected and happens even without this patch. update_balloon_stats() also calls si_meminfo(). It is a bit more complex function. It too just reads some variables and looks lock-less safe. In each case, it seems to be called lock-less on several similar locations, e.g. from post_status() in dm_thread_func(), or from vmballoon_send_get_target(). The communication with the host is done via a separate virtqueue, see vb->stats_vq vs. vb->inflate_vq and vb->deflate_vq. Therefore it could be used in parallel with fill_balloon() and leak_balloon(). This patch splits the existing work into two pieces. One is for updating the balloon stats. The other is for resizing of the balloon. It seems that they can be proceed in parallel without any extra locking. Signed-off-by: Petr Mladek Signed-off-by: Michael S. Tsirkin --- drivers/virtio/virtio_balloon.c | 36 +++++++++++++++++++++--------------- 1 file changed, 21 insertions(+), 15 deletions(-) (limited to 'drivers/virtio/virtio_balloon.c') diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index 2c9a92f1e525..9057cc768ca5 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -49,7 +49,8 @@ struct virtio_balloon { struct virtqueue *inflate_vq, *deflate_vq, *stats_vq; /* The balloon servicing is delegated to a freezable workqueue. */ - struct work_struct work; + struct work_struct update_balloon_stats_work; + struct work_struct update_balloon_size_work; /* Prevent updating balloon when it is being canceled. */ spinlock_t stop_update_lock; @@ -76,7 +77,6 @@ struct virtio_balloon { u32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX]; /* Memory statistics */ - int need_stats_update; struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR]; /* To register callback in oom notifier call chain */ @@ -123,6 +123,7 @@ static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq) /* When host has read buffer, this completes via balloon_ack */ wait_event(vb->acked, virtqueue_get_buf(vq, &len)); + } static void set_page_pfns(u32 pfns[], struct page *page) @@ -262,11 +263,9 @@ static void stats_request(struct virtqueue *vq) { struct virtio_balloon *vb = vq->vdev->priv; - vb->need_stats_update = 1; - spin_lock(&vb->stop_update_lock); if (!vb->stop_update) - queue_work(system_freezable_wq, &vb->work); + queue_work(system_freezable_wq, &vb->update_balloon_stats_work); spin_unlock(&vb->stop_update_lock); } @@ -276,7 +275,6 @@ static void stats_handle_request(struct virtio_balloon *vb) struct scatterlist sg; unsigned int len; - vb->need_stats_update = 0; update_balloon_stats(vb); vq = vb->stats_vq; @@ -294,7 +292,7 @@ static void virtballoon_changed(struct virtio_device *vdev) spin_lock_irqsave(&vb->stop_update_lock, flags); if (!vb->stop_update) - queue_work(system_freezable_wq, &vb->work); + queue_work(system_freezable_wq, &vb->update_balloon_size_work); spin_unlock_irqrestore(&vb->stop_update_lock, flags); } @@ -358,17 +356,24 @@ static int virtballoon_oom_notify(struct notifier_block *self, return NOTIFY_OK; } -static void balloon(struct work_struct *work) +static void update_balloon_stats_func(struct work_struct *work) +{ + struct virtio_balloon *vb; + + vb = container_of(work, struct virtio_balloon, + update_balloon_stats_work); + stats_handle_request(vb); +} + +static void update_balloon_size_func(struct work_struct *work) { struct virtio_balloon *vb; s64 diff; - vb = container_of(work, struct virtio_balloon, work); + vb = container_of(work, struct virtio_balloon, + update_balloon_size_work); diff = towards_target(vb); - if (vb->need_stats_update) - stats_handle_request(vb); - if (diff > 0) diff -= fill_balloon(vb, diff); else if (diff < 0) @@ -494,14 +499,14 @@ static int virtballoon_probe(struct virtio_device *vdev) goto out; } - INIT_WORK(&vb->work, balloon); + INIT_WORK(&vb->update_balloon_stats_work, update_balloon_stats_func); + INIT_WORK(&vb->update_balloon_size_work, update_balloon_size_func); spin_lock_init(&vb->stop_update_lock); vb->stop_update = false; vb->num_pages = 0; mutex_init(&vb->balloon_lock); init_waitqueue_head(&vb->acked); vb->vdev = vdev; - vb->need_stats_update = 0; balloon_devinfo_init(&vb->vb_dev_info); #ifdef CONFIG_BALLOON_COMPACTION @@ -552,7 +557,8 @@ static void virtballoon_remove(struct virtio_device *vdev) spin_lock_irq(&vb->stop_update_lock); vb->stop_update = true; spin_unlock_irq(&vb->stop_update_lock); - cancel_work_sync(&vb->work); + cancel_work_sync(&vb->update_balloon_size_work); + cancel_work_sync(&vb->update_balloon_stats_work); remove_common(vb); kfree(vb); -- cgit v1.2.3-59-g8ed1b