Re: [Qemu-devel] [RFC 27/29] migration: setup ramstate for resume

[Dr. David Alan Gilbert]

* Peter Xu (address@hidden) wrote:
> After we updated the dirty bitmaps of ramblocks, we also need to update
> the critical fields in RAMState to make sure it is ready for a resume.
> 
> Signed-off-by: Peter Xu <address@hidden>
> ---
>  migration/ram.c | 35 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index c695b13..427bf6e 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -1947,6 +1947,31 @@ static int ram_state_init(RAMState **rsp)
>      return 0;
>  }
>  
> +static void ram_state_resume_prepare(RAMState *rs)
> +{
> +    RAMBlock *block;
> +    long pages = 0;
> +
> +    /*
> +     * Postcopy is not using xbzrle/compression, so no need for that.
> +     * Also, since source are already halted, we don't need to care
> +     * about dirty page logging as well.
> +     */
> +
> +    RAMBLOCK_FOREACH(block) {
> +        pages += bitmap_count_one(block->bmap,
> +                                  block->max_length >> TARGET_PAGE_BITS);

Again I think that needs to be block->used_length (see
migration_bitmap_sync).

> +    }
> +
> +    /* This may not be aligned with current bitmaps. Recalculate. */
> +    rs->migration_dirty_pages = pages;
> +
> +    rs->last_seen_block = NULL;
> +    rs->last_sent_block = NULL;
> +    rs->last_page = 0;
> +    rs->last_version = ram_list.version;

A trace at this point with the pages count might be worthwhile.

> +}
> +
>  /*
>   * Each of ram_save_setup, ram_save_iterate and ram_save_complete has
>   * long-running RCU critical section.  When rcu-reclaims in the code
> @@ -2842,8 +2867,16 @@ int ram_dirty_bitmap_reload(MigrationState *s, 
> RAMBlock *block)
>  static int ram_resume_prepare(MigrationState *s, void *opaque)
>  {
>      RAMState *rs = *(RAMState **)opaque;
> +    int ret;
>  
> -    return ram_dirty_bitmap_sync_all(s, rs);
> +    ret = ram_dirty_bitmap_sync_all(s, rs);

Interesting; I'd assumed you'd load directly into this
bitmap rather than loading into the bitmap on each block.
Do we ever get the case where a bitmap is set on the source
bitmap but not in the loaded bitmap?

Dave

> +    if (ret) {
> +        return ret;
> +    }
> +
> +    ram_state_resume_prepare(rs);
> +
> +    return 0;
>  }
>  
>  static SaveVMHandlers savevm_ram_handlers = {
> -- 
> 2.7.4
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK