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Subject: Re: [PATCH v36 2/5] virtio_balloon: replace oom notifier with shrinker
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 failthen. 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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