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

On 04/13/2018 02:51 PM, Michael S. Tsirkin wrote:
On Fri, Apr 13, 2018 at 10:10:57AM -0700, Jonathan Helman wrote:

On 04/13/2018 06:44 AM, Michael S. Tsirkin wrote:
On Fri, Apr 13, 2018 at 03:01:11PM +0800, Jason Wang wrote:

On 2018年04月12日 08:24, Jonathan Helman wrote:

On 04/10/2018 08:12 PM, Jason Wang wrote:

On 2018年04月10日 05:11, Jonathan Helman wrote:

On 03/22/2018 07:38 PM, Jason Wang wrote:

On 2018年03月22日 11:10, Michael S. Tsirkin wrote:
On Thu, Mar 22, 2018 at 09:52:18AM +0800, Jason Wang wrote:
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

Signed-off-by: Jonathan Helman<jonathan.helman@oracle.com>
Reviewed-by: Jason Wang<jasowang@redhat.com>

     drivers/virtio/virtio_balloon.c     | 6 ++++++
     include/uapi/linux/virtio_balloon.h | 4 +++-
     2 files changed, 9 insertions(+), 1 deletion(-)

diff --git
index dfe5684..6b237e3 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -272,6 +272,12 @@ static unsigned int
virtio_balloon *vb)
         update_stat(vb, idx++,
         update_stat(vb, idx++,
+    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]);
         update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
diff --git
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
8  /* Hugetlb page allocations */
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?

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.

Suggestions? I don't like to break build for people ...

Didn't have a good idea. But maybe we should keep
VIRTIO_BALLOON_S_NR unchanged, and add a comment here.


I think Jason's comment is for a future patch. Didn't see this
patch get applied, so wondering if it could be.


Hi Jon:

Have you tested new driver with old qemu?

Yes, this testing scenario looks good. Thanks.


Hi Jon:

I mean e.g compiling qemu with new linux headers. E.g current qemu has:

static const char *balloon_stat_names[] = {
     [VIRTIO_BALLOON_S_SWAP_IN] = "stat-swap-in",
     [VIRTIO_BALLOON_S_SWAP_OUT] = "stat-swap-out",
     [VIRTIO_BALLOON_S_MAJFLT] = "stat-major-faults",
     [VIRTIO_BALLOON_S_MINFLT] = "stat-minor-faults",
     [VIRTIO_BALLOON_S_MEMFREE] = "stat-free-memory",
     [VIRTIO_BALLOON_S_MEMTOT] = "stat-total-memory",
     [VIRTIO_BALLOON_S_AVAIL] = "stat-available-memory",
     [VIRTIO_BALLOON_S_CACHES] = "stat-disk-caches",

I'm afraid it will be broken if VIRTIO_BALLOON_S_NR is 10.


Well it is handy for sizing arrays and this isn't the first time we did

commit 4d32029b8ddb7be4d1699c6d8e1675ff5476d149
Author: Tomáš Golembiovský <tgolembi@redhat.com>
Date:   Sun Nov 12 13:05:38 2017 +0100

      virtio_balloon: include disk/file caches memory statistics

commit 5057dcd0f1aaad57e07e728ba20a99e205c6b9de
Author: Igor Redko <redkoi@virtuozzo.com>
Date:   Thu Mar 17 14:19:08 2016 -0700

      virtio_balloon: export 'available' memory to balloon statistics

how about we give QEMU a hand and just put the list of names in
the header?

I posted a patch like that, pls review.

Sorry, maybe I'm missing something. We have an internal copy of the header
file in qemu under include/standard-headers/linux/virtio_balloon.h, which
hw/virtio/virtio-balloon.c includes (through including
hw/virtio/virtio-balloon.h). I thought qemu would use internal header files
so that it could be compiled on any Linux kernel version. So when would we
ever have the issue Jason is discussing?


Whenever we update the headers.

Ah got it. Updating the headers without updating that string array breaks things. Thanks.

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