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Subject: Re: [PATCH v4 4/4] migration: use the free page hint feature from balloon
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()) {
... }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
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