On Fri, Nov 26, 2021 at 02:42:07PM +0100, David Hildenbrand wrote:

The virtio-mem driver currently supports logical hot(un)plug in
MAX_ORDER - 1 granularity (4MiB on x86-64) or bigger. We want to support
pageblock granularity (2MiB on x86-64), to make hot(un)plug even more
flexible, and to improve hotunplug when using ZONE_NORMAL.

With pageblock granularity, we then have a granularity comparable to
hugepage ballooning. Further, there are ideas to increase MAX_ORDER, so
we really want to decouple it from MAX_ORDER.

While ZONE_MOVABLE should mostly work already, alloc_contig_range() still
needs work to be able to properly handle pageblock granularity on
ZONE_NORMAL. This support is in the works [1], so let's prepare
virtio-mem for supporting smaller granularity than MAX_ORDER - 1.

is there value to merging this seprately? or should this just
be part of that patchset?

Tested with ZONE_MOVABLE after removing the MAX_ORDER - 1 granularity
limitation in virtio-mem, and using different device block sizes (2MiB,
4MiB, 8MiB).

[1] https://lkml.kernel.org/r/20211115193725.737539-1-zi.yan@sent.com

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Gavin Shan <redacted>
Cc: Hui Zhu <redacted>
Cc: Eric Ren <redacted>
Cc: Sebastien Boeuf <redacted>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Wei Yang <redacted>
Cc: virtualization@lists.linux-foundation.org
Cc: linux-mm@kvack.org

David Hildenbrand (2):
  virtio-mem: prepare page onlining code for granularity smaller than
    MAX_ORDER - 1
  virtio-mem: prepare fake page onlining code for granularity smaller
    than MAX_ORDER - 1

 drivers/virtio/virtio_mem.c | 110 ++++++++++++++++++++++++------------
 1 file changed, 74 insertions(+), 36 deletions(-)

-- 
2.31.1