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Subject: Re: [PATCH v4 4/4] migration: use the free page hint feature from balloon
On Wed, Mar 14, 2018 at 10:41:36AM +0800, Wei Wang wrote: > 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© 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 <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> > > > --- > > > 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()) { > ... > } Hard to tell on the outset. E.g. why is just stop affected? Pls add comments explaining what happens if VM is not running when start or stop is called. > 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. But you need to wake it up and notify the guest presumably? > > > > /** > > > @@ -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
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