On 03.06.19 19:03, Nitesh Narayan Lal wrote: > This patch introduces the core infrastructure for free page hinting in > virtual environments. It enables the kernel to track the free pages which > can be reported to its hypervisor so that the hypervisor could > free and reuse that memory as per its requirement. > > While the pages are getting processed in the hypervisor (e.g., > via MADV_FREE), the guest must not use them, otherwise, data loss > would be possible. To avoid such a situation, these pages are > temporarily removed from the buddy. The amount of pages removed > temporarily from the buddy is governed by the backend(virtio-balloon > in our case). > > To efficiently identify free pages that can to be hinted to the > hypervisor, bitmaps in a coarse granularity are used. Only fairly big > chunks are reported to the hypervisor - especially, to not break up THP > in the hypervisor - "MAX_ORDER - 2" on x86, and to save space. The bits > in the bitmap are an indication whether a page *might* be free, not a > guarantee. A new hook after buddy merging sets the bits. > > Bitmaps are stored per zone, protected by the zone lock. A workqueue > asynchronously processes the bitmaps, trying to isolate and report pages > that are still free. The backend (virtio-balloon) is responsible for > reporting these batched pages to the host synchronously. Once reporting/ > freeing is complete, isolated pages are returned back to the buddy. > > There are still various things to look into (e.g., memory hotplug, more > efficient locking, possible races when disabling). > > Signed-off-by: Nitesh Narayan Lal <nitesh@xxxxxxxxxx> > --- > drivers/virtio/Kconfig | 1 + > include/linux/page_hinting.h | 46 +++++++ > mm/Kconfig | 6 + > mm/Makefile | 2 + > mm/page_alloc.c | 17 +-- > mm/page_hinting.c | 236 +++++++++++++++++++++++++++++++++++ > 6 files changed, 301 insertions(+), 7 deletions(-) > create mode 100644 include/linux/page_hinting.h > create mode 100644 mm/page_hinting.c > > diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig > index 35897649c24f..5a96b7a2ed1e 100644 > --- a/drivers/virtio/Kconfig > +++ b/drivers/virtio/Kconfig > @@ -46,6 +46,7 @@ config VIRTIO_BALLOON > tristate "Virtio balloon driver" > depends on VIRTIO > select MEMORY_BALLOON > + select PAGE_HINTING > ---help--- > This driver supports increasing and decreasing the amount > of memory within a KVM guest. BTW, this hunk belongs to the virtio-balloon patch. -- Thanks, David / dhildenb
