Re: [PATCH 2/6] md-cluster: Avoid the resync ping-pong

[NeilBrown <neilb@suse.com>]

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On Fri, Nov 06 2015, rgoldwyn@suse.de wrote:

> From: Goldwyn Rodrigues <rgoldwyn@suse.com>
>
> If a RESYNCING message with (0,0) has been sent before, do not send it
> again. This avoids a resync ping pong between the nodes. We read
> the bitmap lockresource's LVB to figure out the previous value
> of the RESYNCING message.

This seems like a bandaid more than a real fix, but maybe I'm wrong.
I'll apply it for now.  If I end of figuring out that there is some
other issue I discuss it then.

>
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> ---
>  drivers/md/md-cluster.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/drivers/md/md-cluster.c b/drivers/md/md-cluster.c
> index a93734e..3daa464 100644
> --- a/drivers/md/md-cluster.c
> +++ b/drivers/md/md-cluster.c
> @@ -898,8 +898,16 @@ static int resync_start(struct mddev *mddev)
>  static int resync_info_update(struct mddev *mddev, sector_t lo, sector_t hi)
>  {
>  	struct md_cluster_info *cinfo = mddev->cluster_info;
> +	struct resync_info ri;
>  	struct cluster_msg cmsg = {0};
>  
> +	/* do not send zero again, if we have sent before */
> +	if (hi == 0) {
> +		memcpy(&ri, cinfo->bitmap_lockres->lksb.sb_lvbptr, sizeof(struct resync_info));
> +		if (le64_to_cpu(ri.hi) == 0)
> +			return 0;

I feel this would look so much better as:
        if (hi == 0) { 
               struct resync_info ri;
               memcpy(&ri, cinfo->bitmap_lockres->lksb.sb_lvbptr,
                      sizeof(ri));
        }

so if you happened to resend it like that I'd probably remove what I
have already applied and use this instead.
(make variable more local, use sizeof(var) instead of sizeof(type), and
wrap the long line)

Thanks,
NeilBrown

> +	}
> +
>  	add_resync_info(mddev, cinfo->bitmap_lockres, lo, hi);
>  	/* Re-acquire the lock to refresh LVB */
>  	dlm_lock_sync(cinfo->bitmap_lockres, DLM_LOCK_PW);
> -- 
> 1.8.5.6

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