Re: [Qemu-devel] [PATCH v6 21/28] 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        | 40 +++++++++++++++++++++++++++++++++++++++-
>  migration/trace-events |  1 +
>  2 files changed, 40 insertions(+), 1 deletion(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index a2a4b05d5c..d275875f54 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -2250,6 +2250,36 @@ static int ram_init_all(RAMState **rsp)
>      return 0;
>  }
>  
> +static void ram_state_resume_prepare(RAMState *rs, QEMUFile *out)
> +{
> +    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->used_length >> TARGET_PAGE_BITS);
> +    }
> +
> +    /* This may not be aligned with current bitmaps. Recalculate. */
> +    rs->migration_dirty_pages = pages;

migration_dirty_pages is uint64_t - so we should probably do the cast
above and keep 'pages' as uint64_t.

> +    rs->last_seen_block = NULL;
> +    rs->last_sent_block = NULL;
> +    rs->last_page = 0;
> +    rs->last_version = ram_list.version;

Do you need to explicitly set
       rs->ram_bulk_stage = false;

if the failure happened just after the start of postcopy and no
requested pages had been sent, I think it might still  be set?


> +    /* Update RAMState cache of output QEMUFile */
> +    rs->f = out;
> +
> +    trace_ram_state_resume_prepare(pages);
> +}
> +
>  /*
>   * Each of ram_save_setup, ram_save_iterate and ram_save_complete has
>   * long-running RCU critical section.  When rcu-reclaims in the code
> @@ -3178,8 +3208,16 @@ out:
>  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);
> +    if (ret) {
> +        return ret;
> +    }
> +
> +    ram_state_resume_prepare(rs, s->to_dst_file);
> +
> +    return 0;
>  }
>  
>  static SaveVMHandlers savevm_ram_handlers = {
> diff --git a/migration/trace-events b/migration/trace-events
> index 45b1d89217..f5913ff51c 100644
> --- a/migration/trace-events
> +++ b/migration/trace-events
> @@ -88,6 +88,7 @@ ram_dirty_bitmap_reload_complete(char *str) "%s"
>  ram_dirty_bitmap_sync_start(void) ""
>  ram_dirty_bitmap_sync_wait(void) ""
>  ram_dirty_bitmap_sync_complete(void) ""
> +ram_state_resume_prepare(long v) "%ld"
>  
>  # migration/migration.c
>  await_return_path_close_on_source_close(void) ""

Dave

> -- 
> 2.14.3
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK