virtio — archive

[Michael S. Tsirkin]

Document the new option, and also clarify behaviour without it. In particular, I noticed that actual field is not the actual number of pages in the balloon as driver might do inflate followed by deflate. Signed-off-by: Michael S. Tsirkin <mst@redhat.com> --- content.tex 25 +++++++++++++++++++++++-- 1 file changed, 23 insertions(+), 2 deletions(-) diff --git a/content.tex b/content.tex index 036f38c..98d5486 100644 --- a/content.tex +++ b/content.tex @@ -4390,6 +4390,9 @@ guest memory statistics to the host. item[VIRTIO_BALLOON_F_STATS_VQ (1)] A virtqueue for reporting guest memory statistics is present. +item[VIRTIO_BALLOON_F_DEFLATE_ON_OOM (2) ] Deflate balloon on + OOM. + end{description} drivernormative{subsubsection}{Feature bits}{Device Types / Memory Balloon Device / Feature bits} @@ -4489,10 +4492,25 @@ requests by using the descriptor. drivernormative{subsubsection}{Device Operation}{Device Types / Memory Balloon Device / Device Operation} The driver SHOULD supply pages to the balloon when field{num_pages} is -greater than field{actual}. +greater than the actual number of pages in the balloon. The driver MAY use pages from the balloon when field{num_pages} is -less than field{actual}. +less than the actual number of pages in the balloon. + +The driver MAY supply pages to the balloon when field{num_pages} is +greater than or equal to the actual number of pages in the balloon. + +If VIRTIO_BALLOON_F_DEFLATE_ON_OOM has not been negotiated, the +driver MUST NOT use pages from the balloon when field{num_pages} +is less than or equal to the actual number of pages in the +balloon. + +If VIRTIO_BALLOON_F_DEFLATE_ON_OOM has been negotiated, the +driver MAY use pages from the balloon when field{num_pages} +is less than or equal to the actual number of pages in the +balloon if this is required for system stability +(e.g. if memory is required by applications running within + the guest). The driver MUST use the deflateq to inform the device of pages that it wants to use from the balloon. @@ -4517,6 +4535,9 @@ request. The driver MUST update field{actual} after changing the number of pages in the balloon. +The driver MAY update field{actual} once after multiple +inflate and deflate operations. + devicenormative{subsubsection}{Device Operation}{Device Types / Memory Balloon Device / Device Operation} The device MAY modify the contents of a page in the balloon -- MST