On 07/22/2018 10:48 PM, Michael S. Tsirkin wrote:
On Fri, Jul 20, 2018 at 04:33:02PM +0800, Wei Wang wrote:
+static unsigned long virtio_balloon_shrinker_scan(struct shrinker *shrinker,
+ struct shrink_control *sc)
+{
+ unsigned long pages_to_free = balloon_pages_to_shrink,
+ pages_freed = 0;
+ struct virtio_balloon *vb = container_of(shrinker,
+ struct virtio_balloon, shrinker);
+
+ /*
+ * One invocation of leak_balloon can deflate at most
+ * VIRTIO_BALLOON_ARRAY_PFNS_MAX balloon pages, so we call it
+ * multiple times to deflate pages till reaching
+ * balloon_pages_to_shrink pages.
+ */
+ while (vb->num_pages && pages_to_free) {
+ pages_to_free = balloon_pages_to_shrink - pages_freed;
+ pages_freed += leak_balloon(vb, pages_to_free);
+ }
+ update_balloon_size(vb);
Are you sure that this is never called if count returned 0?
Yes. Please see do_shrink_slab, it just returns if count is 0.
+
+ return pages_freed / VIRTIO_BALLOON_PAGES_PER_PAGE;
+}
+
+static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker,
+ struct shrink_control *sc)
+{
+ struct virtio_balloon *vb = container_of(shrinker,
+ struct virtio_balloon, shrinker);
+
+ /*
+ * We continue to use VIRTIO_BALLOON_F_DEFLATE_ON_OOM to handle the
+ * case when shrinker needs to be invoked to relieve memory pressure.
+ */
+ if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
+ return 0;
So why not skip notifier registration when deflate on oom
is clear?
Sounds good, thanks.
vb->vb_dev_info.inode->i_mapping->a_ops = &balloon_aops;
#endif
+ err = virtio_balloon_register_shrinker(vb);
+ if (err)
+ goto out_del_vqs;
So we can get scans before device is ready. Leak will fail
then. Why not register later after device is ready?
Probably no.
- it would be better not to set device ready when register_shrinker failed.
- When the device isn't ready, ballooning won't happen, that is,
vb->num_pages will be 0, which results in shrinker_count=0 and
shrinker_scan won't be called.
So I think it would be better to have shrinker registered before
device_ready.
Best,
Wei
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