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SubjectRe: [PATCH RFC] virtio_balloon: conservative balloon page shrinking
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On 06.02.20 09:01, Wei Wang wrote:
> There are cases that users want to shrink balloon pages after the
> pagecache depleted. The conservative_shrinker lets the shrinker
> shrink balloon pages when all the pagecache has been reclaimed.
>
> Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> ---
> drivers/virtio/virtio_balloon.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 93f995f6cf36..b4c5bb13a867 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -42,6 +42,10 @@
> static struct vfsmount *balloon_mnt;
> #endif
>
> +static bool conservative_shrinker = true;
> +module_param(conservative_shrinker, bool, 0644);
> +MODULE_PARM_DESC(conservative_shrinker, "conservatively shrink balloon pages");
> +
> enum virtio_balloon_vq {
> VIRTIO_BALLOON_VQ_INFLATE,
> VIRTIO_BALLOON_VQ_DEFLATE,
> @@ -796,6 +800,10 @@ static unsigned long shrink_balloon_pages(struct virtio_balloon *vb,
> {
> unsigned long pages_freed = 0;
>
> + /* Balloon pages only gets shrunk when the pagecache depleted */
> + if (conservative_shrinker && global_node_page_state(NR_FILE_PAGES))
> + return 0;
> +
> /*
> * One invocation of leak_balloon can deflate at most
> * VIRTIO_BALLOON_ARRAY_PFNS_MAX balloon pages, so we call it
> @@ -837,7 +845,11 @@ static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker,
> struct virtio_balloon, shrinker);
> unsigned long count;
>
> - count = vb->num_pages / VIRTIO_BALLOON_PAGES_PER_PAGE;
> + if (conservative_shrinker && global_node_page_state(NR_FILE_PAGES))
> + count = 0;
> + else
> + count = vb->num_pages / VIRTIO_BALLOON_PAGES_PER_PAGE;
> +
> count += vb->num_free_page_blocks * VIRTIO_BALLOON_HINT_BLOCK_PAGES;
>
> return count;
>

so dropping caches (echo 3 > /proc/sys/vm/drop_caches) will no longer
deflate the balloon when conservative_shrinker=true?

--
Thanks,

David / dhildenb

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