Re: [Qemu-devel] [PULL 5/5] migratioin/ram: leave RAMBlock->bmap blank on allocating

[Wei Yang <richard.weiyang@gmail.com>]

On Wed, Jun 05, 2019 at 01:53:18PM +0200, Juan Quintela wrote:
>From: 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>
>Reviewed-by: Juan Quintela <quintela@redhat.com>
>Signed-off-by: Juan Quintela <quintela@redhat.com>

I think Peter acked this and gave some suggestions.

>---
> migration/ram.c | 18 +++++++++++++-----
> 1 file changed, 13 insertions(+), 5 deletions(-)
>
>diff --git a/migration/ram.c b/migration/ram.c
>index 03a9cce9f9..082aea9d23 100644
>--- a/migration/ram.c
>+++ b/migration/ram.c
>@@ -3173,11 +3173,11 @@ static int ram_state_init(RAMState **rsp)
>     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.
>+     * This must match with the initial values of dirty bitmap.
>+     * Currently we initialize the dirty bitmap to all zeros so
>+     * here the total dirty page count is zero.
>      */
>-    (*rsp)->migration_dirty_pages = ram_bytes_total() >> TARGET_PAGE_BITS;
>-
>+    (*rsp)->migration_dirty_pages = 0;
>     ram_state_reset(*rsp);
> 
>     return 0;
>@@ -3192,8 +3192,16 @@ static void ram_list_init_bitmaps(void)
>     if (ram_bytes_total()) {
>         RAMBLOCK_FOREACH_NOT_IGNORED(block) {
>             pages = block->max_length >> TARGET_PAGE_BITS;
>+            /*
>+             * The initial dirty bitmap for migration must be set with all
>+             * ones to make sure we'll migrate every guest RAM page to
>+             * destination.
>+             * Here we didn't set RAMBlock.bmap simply because it is already
>+             * set in ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION] in
>+             * ram_block_add, and that's where we'll sync the dirty bitmaps.
>+             * Here setting RAMBlock.bmap would be fine too but not necessary.
>+             */
>             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);
>-- 
>2.21.0
>

-- 
Wei Yang
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