[Qemu-devel] [PATCH v2] migratioin/ram: leave RAMBlock->bmap blank on allocating

[Wei Yang <richardw.yang@linux.intel.com>]

During migration, we would sync bitmap from ram_list.dirty_memory to
RAMBlock.bmap in cpu_physical_memory_sync_dirty_bitmap().

Since we set RAMBlock.bmap and ram_list.dirty_memory both to all 1, this
means at the first round this sync is meaningless and is a duplicated
work.

Leaving RAMBlock->bmap blank on allocating would have a side effect on
migration_dirty_pages, since it is calculated from the result of
cpu_physical_memory_sync_dirty_bitmap(). To keep it right, we need to
set migration_dirty_pages to 0 in ram_state_init().

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

---
v2: add a comment explaining why leaving RAMBlock.bmap clear
---
 migration/ram.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/migration/ram.c b/migration/ram.c
index 4c60869226..e9a27ea5e6 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -3181,12 +3181,7 @@ static int ram_state_init(RAMState **rsp)
     qemu_mutex_init(&(*rsp)->src_page_req_mutex);
     QSIMPLEQ_INIT(&(*rsp)->src_page_requests);
 
-    /*
-     * Count the total number of pages used by ram blocks not including any
-     * gaps due to alignment or unplugs.
-     */
-    (*rsp)->migration_dirty_pages = ram_bytes_total() >> TARGET_PAGE_BITS;
-
+    (*rsp)->migration_dirty_pages = 0;
     ram_state_reset(*rsp);
 
     return 0;
@@ -3201,8 +3196,15 @@ static void ram_list_init_bitmaps(void)
     if (ram_bytes_total()) {
         RAMBLOCK_FOREACH_NOT_IGNORED(block) {
             pages = block->max_length >> TARGET_PAGE_BITS;
+            /*
+             * We leave RAMBlock.bmap clear here and they will be sync from
+             * ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION] in
+             * migration_bitmap_sync_precopy().
+             *
+             * ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION] is set to all 1
+             * in ram_block_add().
+             */
             block->bmap = bitmap_new(pages);
-            bitmap_set(block->bmap, 0, pages);
             if (migrate_postcopy_ram()) {
                 block->unsentmap = bitmap_new(pages);
                 bitmap_set(block->unsentmap, 0, pages);
-- 
2.19.1