[Qemu-devel] [PATCH v1 2/4] migration: call balloon to clear bits of free pages from dirty bitmap

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

When migration starts, call the related balloon functions to clear the
bits of guest free pages from the dirty bitmap. The dirty bitmap should
be ready to use when sending pages to the destination, so stop the guest
from reporting free pages before sending pages.

Signed-off-by: Wei Wang <wei.w.wang@intel.com>
CC: Michael S. Tsirkin <mst@redhat.com>
---
 migration/ram.c | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/migration/ram.c b/migration/ram.c
index d6f462c..9b8d102 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -49,6 +49,7 @@
 #include "qemu/rcu_queue.h"
 #include "migration/colo.h"
 #include "migration/block.h"
+#include "sysemu/balloon.h"
 
 /***********************************************************/
 /* ram save/restore */
@@ -206,6 +207,10 @@ struct RAMState {
     uint32_t last_version;
     /* We are in the first round */
     bool ram_bulk_stage;
+    /* The feature, skipping the transfer of free pages, is supported */
+    bool free_page_support;
+    /* Skip the transfer of free pages in the bulk stage */
+    bool free_page_done;
     /* How many times we have dirty too many pages */
     int dirty_rate_high_cnt;
     /* these variables are used for bitmap sync */
@@ -773,7 +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);
@@ -1653,6 +1658,8 @@ 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();
+    rs->free_page_done = false;
 }
 
 #define MAX_WAIT 50 /* ms, half buffered_file limit */
@@ -2135,7 +2142,7 @@ static int ram_state_init(RAMState **rsp)
     return 0;
 }
 
-static void ram_list_init_bitmaps(void)
+static void ram_list_init_bitmaps(RAMState *rs)
 {
     RAMBlock *block;
     unsigned long pages;
@@ -2145,7 +2152,11 @@ static void ram_list_init_bitmaps(void)
         QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
             pages = block->max_length >> TARGET_PAGE_BITS;
             block->bmap = bitmap_new(pages);
-            bitmap_set(block->bmap, 0, pages);
+            if (rs->free_page_support) {
+                bitmap_set(block->bmap, 1, pages);
+            } else {
+                bitmap_set(block->bmap, 0, pages);
+            }
             if (migrate_postcopy_ram()) {
                 block->unsentmap = bitmap_new(pages);
                 bitmap_set(block->unsentmap, 0, pages);
@@ -2161,8 +2172,11 @@ static void ram_init_bitmaps(RAMState *rs)
     qemu_mutex_lock_ramlist();
     rcu_read_lock();
 
-    ram_list_init_bitmaps();
+    ram_list_init_bitmaps(rs);
     memory_global_dirty_log_start();
+    if (rs->free_page_support) {
+        balloon_free_page_start();
+    }
     migration_bitmap_sync(rs);
 
     rcu_read_unlock();
@@ -2275,6 +2289,12 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
 
     ram_control_before_iterate(f, RAM_CONTROL_ROUND);
 
+    /* Before sending the pages, stop the guest from reporting free pages. */
+    if (rs->free_page_support && !rs->free_page_done) {
+        balloon_free_page_stop();
+        rs->free_page_done = true;
+    }
+
     t0 = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
     i = 0;
     while ((ret = qemu_file_rate_limit(f)) == 0) {
-- 
1.8.3.1