Re: [PATCH v1 0/8] virtio-mem: Support "prealloc=on"

[Michal Prívozník]

On 11/30/21 11:41, David Hildenbrand wrote:
> Based-on: <20211130092838.24224-1-david@redhat.com>
> 
> Patch #1 - #7 are fully reviewed [1] but did not get picked up yet, so I'm
> sending them along here, as they are required to use os_mem_prealloc() in
> a safe way once the VM is running.
> 
> Support preallocation of memory to make virtio-mem safe to use with
> scarce memory resources such as hugetlb. Before acknowledging a plug
> request from the guest, we'll try preallcoating memory. If that fails,
> we'll fail the request gracefully and warn the usr once.
> 
> To fully support huge pages for shared memory, we'll have to adjust shared
> memory users, such as virtiofsd, to map guest memory via MAP_NORESERVE as
> well, because otherwise, they'll end up overwriting the "reserve=off"
> decision made by QEMU and try reserving huge pages for the sparse memory
> region.
> 
> In the future, we might want to process guest requests, including
> preallocating memory, asynchronously via a dedicated iothread.
> 
> [1] https://lkml.kernel.org/r/20211004120208.7409-1-david@redhat.com
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: Igor Mammedov <imammedo@redhat.com>
> Cc: Eduardo Habkost <ehabkost@redhat.com>
> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Cc: Daniel P. Berrangé <berrange@redhat.com>
> Cc: Gavin Shan <gshan@redhat.com>
> Cc: Hui Zhu <teawater@gmail.com>
> Cc: Sebastien Boeuf <sebastien.boeuf@intel.com>
> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
> Cc: Michal Prívozník <mprivozn@redhat.com>
> 
> David Hildenbrand (8):
>   util/oslib-posix: Let touch_all_pages() return an error
>   util/oslib-posix: Support MADV_POPULATE_WRITE for os_mem_prealloc()
>   util/oslib-posix: Introduce and use MemsetContext for
>     touch_all_pages()
>   util/oslib-posix: Don't create too many threads with small memory or
>     little pages
>   util/oslib-posix: Avoid creating a single thread with
>     MADV_POPULATE_WRITE
>   util/oslib-posix: Support concurrent os_mem_prealloc() invocation
>   util/oslib-posix: Forward SIGBUS to MCE handler under Linux
>   virtio-mem: Support "prealloc=on" option
> 
>  hw/virtio/virtio-mem.c         |  39 +++++-
>  include/hw/virtio/virtio-mem.h |   4 +
>  include/qemu/osdep.h           |   7 +
>  softmmu/cpus.c                 |   4 +
>  util/oslib-posix.c             | 231 +++++++++++++++++++++++++--------
>  5 files changed, 226 insertions(+), 59 deletions(-)
> 

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

Michal