Re: [Qemu-devel] [PATCH v2 1/1] virtio_balloon: include buffers and cached memory statistics

[Tomáš Golembiovský]

On Tue, 31 Oct 2017 18:15:48 +0200
"Michael S. Tsirkin" <address@hidden> wrote:

> On Tue, Oct 31, 2017 at 01:20:19PM +0100, Tomáš Golembiovský wrote:
> > ping
> > 
> > +Gil, +Amnon... could you maybe aid in reviewing the patch, please?
> > 
> > 
> >     Tomas
> > 
> > On Sun, 22 Oct 2017 20:05:57 +0200
> > Tomáš Golembiovský <address@hidden> wrote:
> > 
> > > On Thu, 19 Oct 2017 16:12:20 +0300
> > > "Michael S. Tsirkin" <address@hidden> wrote:
> > > 
> > > > On Thu, Sep 21, 2017 at 02:55:41PM +0200, Tomáš Golembiovský wrote:  
> > > > > Add a new fields, VIRTIO_BALLOON_S_BUFFERS and 
> > > > > VIRTIO_BALLOON_S_CACHED,
> > > > > to virtio_balloon memory statistics protocol. The values correspond to
> > > > > 'Buffers' and 'Cached' in /proc/meminfo.
> > > > > 
> > > > > To be able to compute the value of 'Cached' memory it is necessary to
> > > > > export total_swapcache_pages() to modules.
> > > > > 
> > > > > Signed-off-by: Tomáš Golembiovský <address@hidden>  
> > > > 
> > > > Does 'Buffers' actually make sense? It's a temporary storage -
> > > > wouldn't it be significantly out of date by the time
> > > > host receives it?  
> > > 
> > > That would be best answered by somebody from kernel. But my personal
> > > opinion is that it would not be out of date. The amount of memory
> > > dedicated to Buffers does not seem to fluctuate too much.
> > > 
> > >     Tomas
> > > 
> 
> I would be inclined to say, just report
> global_node_page_state(NR_FILE_PAGES).
> Maybe subtract buffer ram.
> 
> It's not clear host cares about the distinction,
> it's all memory that can shrink in response to
> memory pressure such as inflating the balloon.

So in procfs terms we'd be sending sum Cached+SwapCahced.
Martin, would that be good enough?

I wonder whether it would still make sense to send Buffers as a separate
value though. Maybe we should forget about having some granularity here
and just report all the disk caches as one value.

    Tomas

> 
> This statistic is portable as well I think, most guests have
> storage cache.
> 
> 
> > > > > ---
> > > > >  drivers/virtio/virtio_balloon.c     | 11 +++++++++++
> > > > >  include/uapi/linux/virtio_balloon.h |  4 +++-
> > > > >  mm/swap_state.c                     |  1 +
> > > > >  3 files changed, 15 insertions(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/drivers/virtio/virtio_balloon.c 
> > > > > b/drivers/virtio/virtio_balloon.c
> > > > > index f0b3a0b9d42f..c2558ec47a62 100644
> > > > > --- a/drivers/virtio/virtio_balloon.c
> > > > > +++ b/drivers/virtio/virtio_balloon.c
> > > > > @@ -244,12 +244,19 @@ static unsigned int update_balloon_stats(struct 
> > > > > virtio_balloon *vb)
> > > > >       struct sysinfo i;
> > > > >       unsigned int idx = 0;
> > > > >       long available;
> > > > > +     long cached;
> > > > >  
> > > > >       all_vm_events(events);
> > > > >       si_meminfo(&i);
> > > > >  
> > > > >       available = si_mem_available();
> > > > >  
> > > > > +     cached = global_node_page_state(NR_FILE_PAGES) -
> > > > > +                     total_swapcache_pages() - i.bufferram;
> > > > > +     if (cached < 0)
> > > > > +             cached = 0;
> > > > > +
> > > > > +
> > > > >  #ifdef CONFIG_VM_EVENT_COUNTERS
> > > > >       update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
> > > > >                               pages_to_bytes(events[PSWPIN]));
> > > > > @@ -264,6 +271,10 @@ static unsigned int update_balloon_stats(struct 
> > > > > virtio_balloon *vb)
> > > > >                               pages_to_bytes(i.totalram));
> > > > >       update_stat(vb, idx++, VIRTIO_BALLOON_S_AVAIL,
> > > > >                               pages_to_bytes(available));
> > > > > +     update_stat(vb, idx++, VIRTIO_BALLOON_S_BUFFERS,
> > > > > +                             pages_to_bytes(i.bufferram));
> > > > > +     update_stat(vb, idx++, VIRTIO_BALLOON_S_CACHED,
> > > > > +                             pages_to_bytes(cached));
> > > > >  
> > > > >       return idx;
> > > > >  }
> > > > > diff --git a/include/uapi/linux/virtio_balloon.h 
> > > > > b/include/uapi/linux/virtio_balloon.h
> > > > > index 343d7ddefe04..d5dc8a56a497 100644
> > > > > --- a/include/uapi/linux/virtio_balloon.h
> > > > > +++ b/include/uapi/linux/virtio_balloon.h
> > > > > @@ -52,7 +52,9 @@ struct virtio_balloon_config {
> > > > >  #define VIRTIO_BALLOON_S_MEMFREE  4   /* Total amount of free memory 
> > > > > */
> > > > >  #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_NR       7
> > > > > +#define VIRTIO_BALLOON_S_BUFFERS  7   /* Buffers memory as in /proc 
> > > > > */
> > > > > +#define VIRTIO_BALLOON_S_CACHED   8   /* Cached memory as in /proc */
> > > > > +#define VIRTIO_BALLOON_S_NR       9
> > > > >  
> > > > >  /*
> > > > >   * Memory statistics structure.
> > > > > diff --git a/mm/swap_state.c b/mm/swap_state.c
> > > > > index 71ce2d1ccbf7..f3a4ff7d6c52 100644
> > > > > --- a/mm/swap_state.c
> > > > > +++ b/mm/swap_state.c
> > > > > @@ -95,6 +95,7 @@ unsigned long total_swapcache_pages(void)
> > > > >       rcu_read_unlock();
> > > > >       return ret;
> > > > >  }
> > > > > +EXPORT_SYMBOL_GPL(total_swapcache_pages);
> > > > >  
> > > > >  static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);  
> > > > 
> > > > Need an ack from MM crowd on that.
> > > >   
> > > > > -- 
> > > > > 2.14.1  
> > > 
> > > 
> > > -- 
> > > Tomáš Golembiovský <address@hidden>
> > 
> > 
> > -- 
> > Tomáš Golembiovský <address@hidden>


-- 
Tomáš Golembiovský <address@hidden>