Re: [Qemu-devel] [PATCH] migration: always initial RAMBlock.bmap to 1 for new migration

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Ivan Ren (renyime@gmail.com) wrote:
> Reproduce the problem:
> migrate
> migrate_cancel
> migrate
> 
> Error happen for memory migration

Can we fix this by just reverting 03158519384 ?

Dave

> The reason as follows:
> 1. qemu start, ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION] all set to
>    1 by a series of cpu_physical_memory_set_dirty_range
> 2. migration start:ram_init_bitmaps
>    - memory_global_dirty_log_start: begin log diry
>    - memory_global_dirty_log_sync: sync dirty bitmap to
>      ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION]
>    - migration_bitmap_sync_range: sync ram_list.
>      dirty_memory[DIRTY_MEMORY_MIGRATION] to RAMBlock.bmap
>      and ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION] is set to zero
> 3. migration data...
> 4. migrate_cancel, will stop log dirty
> 5. migration start:ram_init_bitmaps
>    - memory_global_dirty_log_start: begin log diry
>    - memory_global_dirty_log_sync: sync dirty bitmap to
>      ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION]
>    - migration_bitmap_sync_range: sync ram_list.
>      dirty_memory[DIRTY_MEMORY_MIGRATION] to RAMBlock.bmap
>      and ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION] is set to zero
> 
>    Here RAMBlock.bmap only have new logged dirty pages, don't contain
>    the whole guest pages.
> 
> Signed-off-by: Ivan Ren <ivanren@tencent.com>
> ---
>  migration/ram.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index 908517fc2b..bbebaee0c1 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 = 0;
> +    (*rsp)->migration_dirty_pages = ram_bytes_total() >> TARGET_PAGE_BITS;
>      ram_state_reset(*rsp);
>  
>      return 0;
> @@ -3196,12 +3196,13 @@ static void ram_list_init_bitmaps(void)
>               * 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.
> +             * Here we set RAMBlock.bmap all to 1 because when rebegin a
> +             * new migration after a failed migration, ram_list.
> +             * dirty_memory[DIRTY_MEMORY_MIGRATION] don't include the whole
> +             * guest memory.
>               */
>              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);
> -- 
> 2.17.2 (Apple Git-113)
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK