Re: [Qemu-devel] [PATCH] migration/postcopy: use static PostcopyDiscardState instead of allocating it for each block

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

* Wei Yang (richardw.yang@linux.intel.com) wrote:
> Even we need to do discard for each RAMBlock, we still can leverage the
> same memory space to store the information.
> 
> By doing so, we avoid memory allocation and deallocation to the system
> and also avoid potential failure of memory allocation which breaks the
> migration.
> 
> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
> ---
>  migration/postcopy-ram.c | 16 +++++++---------
>  1 file changed, 7 insertions(+), 9 deletions(-)
> 
> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> index 9faacacc9e..2e6b076bb7 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -1377,8 +1377,7 @@ void postcopy_fault_thread_notify(MigrationIncomingState *mis)
>   *   asking to discard individual ranges.
>   *
>   * @ms: The current migration state.
> - * @offset: the bitmap offset of the named RAMBlock in the migration
> - *   bitmap.
> + * @offset: the bitmap offset of the named RAMBlock in the migration bitmap.
>   * @name: RAMBlock that discards will operate on.
>   *
>   * returns: a new PDS.
> @@ -1386,13 +1385,14 @@ void postcopy_fault_thread_notify(MigrationIncomingState *mis)
>  PostcopyDiscardState *postcopy_discard_send_init(MigrationState *ms,
>                                                   const char *name)
>  {
> -    PostcopyDiscardState *res = g_malloc0(sizeof(PostcopyDiscardState));
> +    static PostcopyDiscardState res = {0};

Do you think it would be better to make this a static at the top of
migration/postcopy-ram.c and then we could remove the pds parameters
from postcopy_discard_send_range and friends?
If there's only one pds then we don't need to pass the pointer around.

Dave

> -    if (res) {
> -        res->ramblock_name = name;
> -    }
> +    res.ramblock_name = name;
> +    res.cur_entry = 0;
> +    res.nsentwords = 0;
> +    res.nsentcmds = 0;
>  
> -    return res;
> +    return &res;
>  }
>  
>  /**
> @@ -1449,8 +1449,6 @@ void postcopy_discard_send_finish(MigrationState *ms, PostcopyDiscardState *pds)
>  
>      trace_postcopy_discard_send_finish(pds->ramblock_name, pds->nsentwords,
>                                         pds->nsentcmds);
> -
> -    g_free(pds);
>  }
>  
>  /*
> -- 
> 2.17.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK