Re: [virtio-dev] Re: [PATCH v2] virtio_balloon: export hugetlb page allocation counts

[Jason Wang <jasowang@redhat.com>]

On 2018年03月20日 12:26, Jonathan Helman wrote:
> > On Mar 19, 2018, at 7:31 PM, Jason Wang <jasowang@redhat.com> wrote:
> >
> >
> >
> > On 2018年03月20日 06:14, Jonathan Helman wrote:
> > > Export the number of successful and failed hugetlb page
> > > allocations via the virtio balloon driver. These 2 counts
> > > come directly from the vm_events HTLB_BUDDY_PGALLOC and
> > > HTLB_BUDDY_PGALLOC_FAIL.
> > >
> > > Signed-off-by: Jonathan Helman <jonathan.helman@oracle.com>
> > Reviewed-by: Jason Wang <jasowang@redhat.com>
> Thanks.
>
> > > ---
> > >   drivers/virtio/virtio_balloon.c     | 6 ++++++
> > >   include/uapi/linux/virtio_balloon.h | 4 +++-
> > >   2 files changed, 9 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> > > index dfe5684..6b237e3 100644
> > > --- a/drivers/virtio/virtio_balloon.c
> > > +++ b/drivers/virtio/virtio_balloon.c
> > > @@ -272,6 +272,12 @@ static unsigned int update_balloon_stats(struct virtio_balloon *vb)
> > >   				pages_to_bytes(events[PSWPOUT]));
> > >   	update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
> > >   	update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
> > > +#ifdef CONFIG_HUGETLB_PAGE
> > > +	update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGALLOC,
> > > +		    events[HTLB_BUDDY_PGALLOC]);
> > > +	update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGFAIL,
> > > +		    events[HTLB_BUDDY_PGALLOC_FAIL]);
> > > +#endif
> > >   #endif
> > >   	update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
> > >   				pages_to_bytes(i.freeram));
> > > diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
> > > index 4e8b830..40297a3 100644
> > > --- a/include/uapi/linux/virtio_balloon.h
> > > +++ b/include/uapi/linux/virtio_balloon.h
> > > @@ -53,7 +53,9 @@ struct virtio_balloon_config {
> > >   #define VIRTIO_BALLOON_S_MEMTOT   5   /* Total amount of memory */
> > >   #define VIRTIO_BALLOON_S_AVAIL    6   /* Available memory as in /proc */
> > >   #define VIRTIO_BALLOON_S_CACHES   7   /* Disk caches */
> > > -#define VIRTIO_BALLOON_S_NR       8
> > > +#define VIRTIO_BALLOON_S_HTLB_PGALLOC  8  /* Hugetlb page allocations */
> > > +#define VIRTIO_BALLOON_S_HTLB_PGFAIL   9  /* Hugetlb page allocation failures */
> > > +#define VIRTIO_BALLOON_S_NR       10
> > >     /*
> > >    * Memory statistics structure.
> > Not for this patch, but it looks to me that exporting such nr through uapi is fragile.
> Sorry, can you explain what you mean here?
>
> Jon

Spec said "Within an output buffer submitted to the statsq, the device 
MUST ignore entries with tag values that it does not recognize". So 
exporting VIRTIO_BALLOON_S_NR seems useless and device implementation 
can not depend on such number in uapi.

Thanks

> > Thanks
>
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