On Thu, Feb 06, 2020 at 04:01:47PM +0800, 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 <[email protected]>
I'd rather avoid module parameters, but otherwise looks
like a reasonable idea.
Tyler, what do you think?
> ---
> 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))
I'd rather have an API for that in mm/. In particular, do we want other
shrinkers to run, not just pagecache? To pick an example I'm familiar
with, kvm mmu cache for nested virt?
> + 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;
> --
> 2.17.1
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