From 997e120843e82609c8d99a9d5714e6cf91e14cbe Mon Sep 17 00:00:00 2001 From: "Denis V. Lunev" Date: Thu, 20 Aug 2015 00:49:49 +0300 Subject: [PATCH] virtio_balloon: do not change memory amount visible via /proc/meminfo Balloon device is frequently used as a mean of cooperative memory control in between guest and host to manage memory overcommitment. This is the typical case for any hosting workload when KVM guest is provided for end-user. Though there is a problem in this setup. The end-user and hosting provider have signed SLA agreement in which some amount of memory is guaranted for the guest. The good thing is that this memory will be given to the guest when the guest will really need it (f.e. with OOM in guest and with VIRTIO_BALLOON_F_DEFLATE_ON_OOM configuration flag set). The bad thing is that end-user does not know this. Balloon by default reduce the amount of memory exposed to the end-user each time when the page is stolen from guest or returned back by using adjust_managed_page_count and thus /proc/meminfo shows reduced amount of memory. Fortunately the solution is simple, we should just avoid to call adjust_managed_page_count with VIRTIO_BALLOON_F_DEFLATE_ON_OOM set. Signed-off-by: Denis V. Lunev CC: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin --- drivers/virtio/virtio_balloon.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index 8543c9a97307..7efc32945810 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -157,7 +157,9 @@ static void fill_balloon(struct virtio_balloon *vb, size_t num) } set_page_pfns(vb->pfns + vb->num_pfns, page); vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE; - adjust_managed_page_count(page, -1); + if (!virtio_has_feature(vb->vdev, + VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) + adjust_managed_page_count(page, -1); } /* Did we get any? */ @@ -173,7 +175,9 @@ static void release_pages_balloon(struct virtio_balloon *vb) /* Find pfns pointing at start of each page, get pages and free them. */ for (i = 0; i < vb->num_pfns; i += VIRTIO_BALLOON_PAGES_PER_PAGE) { struct page *page = balloon_pfn_to_page(vb->pfns[i]); - adjust_managed_page_count(page, 1); + if (!virtio_has_feature(vb->vdev, + VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) + adjust_managed_page_count(page, 1); put_page(page); /* balloon reference */ } } -- 2.30.2