Re: [PATCH v3 3/3] migration: use the free page hint feature from balloon

[Wei Wang <wei.w.wang@intel.com>]

On 03/07/2018 08:32 PM, Dr. David Alan Gilbert wrote:
> * Wei Wang (wei.w.wang@intel.com) wrote:
> > Start the free page optimization when the bulk stage starts. In case the
> > guest is slow in reporting, actively stops it when the bulk stage ends.
> > The optimization avoids sending guest free pages during the bulk stage.
> > Currently, the optimization is added to precopy only.
> >
> > Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> > CC: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > CC: Juan Quintela <quintela@redhat.com>
> > CC: Michael S. Tsirkin <mst@redhat.com>
> I think this is OK, but with the only problem being that postcopy will
> break;  we need to disable the mechanism if postcopy is enabled.
>
> Dave
>
> > ---
> >   migration/ram.c | 19 ++++++++++++++++++-
> >   1 file changed, 18 insertions(+), 1 deletion(-)
> >
> > diff --git a/migration/ram.c b/migration/ram.c
> > index 769a0f6..f6af7e6 100644
> > --- a/migration/ram.c
> > +++ b/migration/ram.c
> > @@ -51,6 +51,7 @@
> >   #include "qemu/rcu_queue.h"
> >   #include "migration/colo.h"
> >   #include "migration/block.h"
> > +#include "sysemu/balloon.h"
> >   
> >   /***********************************************************/
> >   /* ram save/restore */
> > @@ -208,6 +209,8 @@ 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 +778,7 @@ 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);
> > @@ -1225,6 +1228,10 @@ static bool find_dirty_block(RAMState *rs, PageSearchStatus *pss, bool *again)
> >               /* Flag that we've looped */
> >               pss->complete_round = true;
> >               rs->ram_bulk_stage = false;
> > +            if (rs->free_page_support) {
> > +                balloon_free_page_stop();
> > +                rs->free_page_support = false;
> > +            }
> >               if (migrate_use_xbzrle()) {
> >                   /* If xbzrle is on, stop using the data compression at this
> >                    * point. In theory, xbzrle can do better than compression.
> > @@ -1656,6 +1663,8 @@ 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();

We checked the postcopy here :)

Best,
Wei