Re: [Qemu-devel] [PATCH v4 4/4] migration: use the free page hint feature from balloon

[Wei Wang]

On 03/14/2018 12:35 AM, Michael S. Tsirkin wrote:
> On Wed, Mar 07, 2018 at 08:34:25PM +0800, Wei Wang wrote:
> > Start the free page optimization after the migration bitmap is
> > synchronized. This can't be used in the stop&copy phase since the guest
> > is paused. Make sure the guest reporting has stopped before
> > synchronizing the migration dirty bitmap. Currently, the optimization is
> > added to precopy only.
> >
> > Signed-off-by: Wei Wang <address@hidden>
> > CC: Dr. David Alan Gilbert <address@hidden>
> > CC: Juan Quintela <address@hidden>
> > CC: Michael S. Tsirkin <address@hidden>
> > ---
> >   migration/ram.c | 19 ++++++++++++++++++-
> >   1 file changed, 18 insertions(+), 1 deletion(-)
> >
> > diff --git a/migration/ram.c b/migration/ram.c
> > index e172798..7b4c9b1 100644
> > --- a/migration/ram.c
> > +++ b/migration/ram.c
> > @@ -51,6 +51,8 @@
> >   #include "qemu/rcu_queue.h"
> >   #include "migration/colo.h"
> >   #include "migration/block.h"
> > +#include "sysemu/balloon.h"
> > +#include "sysemu/sysemu.h"
> >   
> >   /***********************************************************/
> >   /* ram save/restore */
> > @@ -208,6 +210,8 @@ struct RAMState {
> >       uint32_t last_version;
> >       /* We are in the first round */
> >       bool ram_bulk_stage;
> > +    /* The free pages optimization feature is supported */
> > +    bool free_page_support;
> >       /* How many times we have dirty too many pages */
> >       int dirty_rate_high_cnt;
> >       /* these variables are used for bitmap sync */
> > @@ -775,7 +779,7 @@ unsigned long migration_bitmap_find_dirty(RAMState *rs, 
> > RAMBlock *rb,
> >       unsigned long *bitmap = rb->bmap;
> >       unsigned long next;
> >   
> > -    if (rs->ram_bulk_stage && start > 0) {
> > +    if (rs->ram_bulk_stage && start > 0 && !rs->free_page_support) {
> >           next = start + 1;
> >       } else {
> >           next = find_next_bit(bitmap, size, start);
> > @@ -833,6 +837,10 @@ static void migration_bitmap_sync(RAMState *rs)
> >       int64_t end_time;
> >       uint64_t bytes_xfer_now;
> >   
> > +    if (rs->free_page_support) {
> > +        balloon_free_page_stop();
> > +    }
> > +
> >       ram_counters.dirty_sync_count++;
> >   
> >       if (!rs->time_last_bitmap_sync) {
> > @@ -899,6 +907,10 @@ static void migration_bitmap_sync(RAMState *rs)
> >       if (migrate_use_events()) {
> >           qapi_event_send_migration_pass(ram_counters.dirty_sync_count, NULL);
> >       }
> > +
> > +    if (rs->free_page_support && runstate_is_running()) {
> > +        balloon_free_page_start();
> > +    }
> >   }
> I think some of these conditions should go into
> balloon_free_page_start/stop.
>
> Checking runstate is generally problematic unless you
> also handle run state change notifiers as it can
> be manipulated from QMP.

How about moving the check of runstate to 
virtio_balloon_poll_free_page_hints:

while (dev->free_page_report_status < FREE_PAGE_REPORT_S_STOP && 
runstate_is_running()) {
...
}

In this case, I think we won't need a notifier - if the run state is 
changed by qmp, the optimization thread will just exist.


> >   
> >   /**
> > @@ -1656,6 +1668,8 @@ static void ram_state_reset(RAMState *rs)
> >       rs->last_page = 0;
> >       rs->last_version = ram_list.version;
> >       rs->ram_bulk_stage = true;
> > +    rs->free_page_support = balloon_free_page_support() &
> > +                            !migration_in_postcopy();
> Probably &&?

OK, will use &&. (Both work well here actually, since all of the values 
here are boolean)


Best,
Wei