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.
>
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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