On Thu, Aug 23, 2012 at 09:33:53PM -0300, Rafael Aquini wrote:
> On Fri, Aug 24, 2012 at 02:36:16AM +0300, Michael S. Tsirkin wrote:
> > I would wake it each time after adding a page, then it
> > can stop waiting when it leaks enough.
> > But again, it's cleaner to just keep tracking all
> > pages, let mm hang on to them by keeping a reference.
> >
Btw, it's also late here, and there still some work to be done around those
bits, but I guess that has potential to get this issue nailed.
> Here is a rough idea on how it's getting:
>
> Basically, I'm have introducing an atomic counter to track isolated pages, I
> also have changed vb->num_pages into an atomic conter. All inc/dec operations
> take place under pages_lock spinlock, and we only perform work under page
> lock.
>
> It's still missing the wait-part (I'll write it during the weekend) and your
> concerns (and mine) will be addressed, IMHO.
>
> ---8<---
> +/*
> + *
> + */
> +static inline void __wait_on_isolated_pages(struct virtio_balloon *vb,
> + size_t num)
> +{
> + /* There are no isolated pages for this balloon device */
> + if (!atomic_read(&vb->num_isolated_pages))
> + return;
> +
> + /* the leak target is smaller than # of pages on vb->pages list */
> + if (num < (atomic_read(&vb->num_pages) -
> + atomic_read(&vb->num_isolated_pages)))
> + return;
> + else {
> + spin_unlock(&vb->pages_lock);
> + /* wait stuff goes here */
> + spin_lock(&vb->pages_lock);
> + }
> +}
> +
> static void leak_balloon(struct virtio_balloon *vb, size_t num)
> {
> - struct page *page;
> + /* The array of pfns we tell the Host about. */
> + unsigned int num_pfns;
> + u32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
>
> /* We can only do one array worth at a time. */
> - num = min(num, ARRAY_SIZE(vb->pfns));
> + num = min(num, ARRAY_SIZE(pfns));
>
> - for (vb->num_pfns = 0; vb->num_pfns < num;
> - vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
> - page = list_first_entry(&vb->pages, struct page, lru);
> - list_del(&page->lru);
> - set_page_pfns(vb->pfns + vb->num_pfns, page);
> - vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
> + for (num_pfns = 0; num_pfns < num;
> + num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
> + struct page *page = NULL;
> + spin_lock(&vb->pages_lock);
> + __wait_on_isolated_pages(vb, num);
> +
> + if (!list_empty(&vb->pages))
> + page = list_first_entry(&vb->pages, struct page, lru);
> + /*
> + * Grab the page lock to avoid racing against threads
> isolating
> + * pages from, or migrating pages back to vb->pages list.
> + * (both tasks are done under page lock protection)
> + *
> + * Failing to grab the page lock here means this page is being
> + * isolated already, or its migration has not finished yet.
> + */
> + if (page && trylock_page(page)) {
> + clear_balloon_mapping(page);
> + list_del(&page->lru);
> + set_page_pfns(pfns + num_pfns, page);
> + atomic_sub(VIRTIO_BALLOON_PAGES_PER_PAGE,
> + &vb->num_pages);
> + unlock_page(page);
> + }
> + spin_unlock(&vb->pages_lock);
> }
>
> /*
> @@ -182,8 +251,10 @@ static void leak_balloon(struct virtio_balloon *vb,
> size_t
> num)
> * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
> * is true, we *have* to do it in this order
> */
> + mutex_lock(&vb->balloon_lock);
> tell_host(vb, vb->deflate_vq);
> - release_pages_by_pfn(vb->pfns, vb->num_pfns);
> + mutex_unlock(&vb->balloon_lock);
> + release_pages_by_pfn(pfns, num_pfns);
> }
> ---8<---
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