Michael S. Tsirkin wrote:
> This is a replacement for
> [PATCH] virtio: avoid possible OOM lockup at virtballoon_oom_notify()
> but unlike that patch it actually deflates on oom even in presence of
> lock contention.
But Wei Wang is proposing VIRTIO_BALLOON_F_SG which will try to allocate
memory, isn't he?
>
> drivers/virtio/virtio_balloon.c | 30 ++++++++++++++++++++++--------
> include/linux/balloon_compaction.h | 38 +++++++++++++++++++++++++++++++++++++-
> mm/balloon_compaction.c | 27 +++++++++++++++++++++------
> 3 files changed, 80 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index f0b3a0b..725e366 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -143,16 +143,14 @@ static void set_page_pfns(struct virtio_balloon *vb,
>
> static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
> {
> - struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
> unsigned num_allocated_pages;
> + unsigned num_pfns;
> + struct page *page;
> + LIST_HEAD(pages);
>
> - /* We can only do one array worth at a time. */
> - num = min(num, ARRAY_SIZE(vb->pfns));
> -
I don't think moving this min() to later is correct, for
"num" can be e.g. 1048576, can't it?
> - mutex_lock(&vb->balloon_lock);
> - for (vb->num_pfns = 0; vb->num_pfns < num;
> - vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
> - struct page *page = balloon_page_enqueue(vb_dev_info);
> + for (num_pfns = 0; num_pfns < num;
> + num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
> + struct page *page = balloon_page_alloc();
>
> if (!page) {
> dev_info_ratelimited(&vb->vdev->dev,
> @@ -162,6 +160,22 @@ static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
> msleep(200);
> break;
> }
> +
> + balloon_page_push(&pages, page);
> + }
If balloon_page_alloc() did not fail, it will queue "num"
(e.g. 1048576) pages into pages list, won't it?
> +
> + /* We can only do one array worth at a time. */
> + num = min(num, ARRAY_SIZE(vb->pfns));
> +
Now we cap "num" to VIRTIO_BALLOON_ARRAY_PFNS_MAX (which is 256), but
> + mutex_lock(&vb->balloon_lock);
> +
> + vb->num_pfns = 0;
> +
> + while ((page = balloon_page_pop(&pages))) {
this loop will repeat for e.g. 1048576 times, and
> + balloon_page_enqueue(&vb->vb_dev_info, page);
> +
> + vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE;
> +
we increment vb->num_pfns for e.g. 1048576 times which will go
beyond VIRTIO_BALLOON_ARRAY_PFNS_MAX array index.
> set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
> vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
> if (!virtio_has_feature(vb->vdev,
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