On Wed, Nov 17, 2021 at 07:06:34PM +0900, David Stevens wrote: > From: David Stevens <[email protected]> > > Add a module parameters to virtio_balloon to allow specifying whether or > not the driver should call adjust_managed_page_count. If the parameter > is set, it overrides the default behavior inferred from the deflate on > OOM flag. This allows the balloon to operate without changing the amount > of memory visible to userspace via /proc/meminfo or sysinfo, even on a > system that cannot set the default on OOM flag. > > The motivation for this patch is to allow userspace to more accurately > take advantage of virtio_balloon's cooperative memory control on a > system without the ability to use deflate on OOM. As it stands, > userspace has no way to know how much memory may be available on such a > system, which makes tasks such as sizing caches impossible. > > When deflate on OOM is not enabled, the current behavior of the > virtio_balloon more or less resembles hotplugging individual pages, at > least from an accounting perspective. This is basically hardcoding the > requirement that totalram_pages must be available to the guest > immediately, regardless of what the host does. While that is a valid > policy, on Linux (which supports memory overcommit) with virtio_balloon > (which is designed to facilitate overcommit in the host), it is not the > only possible policy. > > The param added by this patch allows the guest to operate under the > assumption that pages in the virtio_balloon will generally be made > available when needed. This assumption may not always hold, but when it > is violated, the guest will just fall back to the normal mechanisms for > dealing with overcommitted memory. > > Signed-off-by: David Stevens <[email protected]> > --- > > Another option to achieve similar behavior would be to add a new feature > flag that would be used in conjunction with DEFLATE_ON_OOM to determine > whether or not adjust_managed_page_count should be called. However, I > feel that this sort of policy decision is a little outside the scope of > what the virtio_balloon API deals with. > > --- > drivers/virtio/virtio_balloon.c | 23 ++++++++++++++++++----- > 1 file changed, 18 insertions(+), 5 deletions(-) > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > index c22ff0117b46..17dac286899c 100644 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -133,6 +133,21 @@ static const struct virtio_device_id id_table[] = { > { 0 }, > }; > > +static char *adjust_pages = ""; > +module_param(adjust_pages, charp, 0); > +MODULE_PARM_DESC(adjust_pages, "Whether or not pages in the balloon should > be removed from the managed page count"); > + > +static bool should_adjust_pages(struct virtio_balloon *vb) > +{ > + if (!strcmp(adjust_pages, "always")) > + return true; > + else if (!strcmp(adjust_pages, "never")) > + return false; > + > + return !virtio_has_feature(vb->vdev, > + VIRTIO_BALLOON_F_DEFLATE_ON_OOM); > +} > + > static u32 page_to_balloon_pfn(struct page *page) > { > unsigned long pfn = page_to_pfn(page); > @@ -243,8 +258,7 @@ static unsigned fill_balloon(struct virtio_balloon *vb, > size_t num) > > set_page_pfns(vb, vb->pfns + vb->num_pfns, page); > vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE; > - if (!virtio_has_feature(vb->vdev, > - VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) > + if (should_adjust_pages(vb)) > adjust_managed_page_count(page, -1); > vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE; > } > @@ -264,8 +278,7 @@ static void release_pages_balloon(struct virtio_balloon > *vb, > struct page *page, *next; > > list_for_each_entry_safe(page, next, pages, lru) { > - if (!virtio_has_feature(vb->vdev, > - VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) > + if (should_adjust_pages(vb)) > adjust_managed_page_count(page, 1); > list_del(&page->lru); > put_page(page); /* balloon reference */ > @@ -775,7 +788,7 @@ static int virtballoon_migratepage(struct > balloon_dev_info *vb_dev_info, > * managed page count when inflating, we have to fixup the count of > * both involved zones. > */ > - if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM) && > + if (should_adjust_pages(vb) && > page_zone(page) != page_zone(newpage)) { > adjust_managed_page_count(page, 1); > adjust_managed_page_count(newpage, -1);
A problem here is that the host also cares: IIUC with VIRTIO_BALLOON_F_STATS_VQ we are sending the info about page counts to host, changing what the stats mean. So I suspect we need a device feature for this at least to control this aspect. > -- > 2.34.0.rc2.393.gf8c9666880-goog _______________________________________________ Virtualization mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/virtualization
