[sheepdog] [PATCH v2 1/2] dog: add a new option for reducing identical snapshots

[Liu Yuan]

On Thu, Feb 12, 2015 at 05:26:59PM +0900, Hitoshi Mitake wrote:
> Current "dog vdi snapshot" command creates a new snapshot
> unconditionally, even if a working VDI doesn't have its own
> objects. In such a case, the created snapshot is redundant because
> same VDI is already existing.
> 
> This patch adds a new option -R to the dog command for reducing
> the identical snapshots.
> 
> Motivations:
> 1. why we need it in dog command instead of combination of parsing
>    "dog vdi list" and existing "dog vdi snapshot"?
> "dog vdi list" tends to be slow in a cluster which has thousands of
> VDIs because it issues bunch of read requests for inode headers. It
> should be avoided as much as possible.
> 2. why identical snapshots harmful?
> Creating identical snapshots means increasing a number of inode
> objects (especially in EC, 16:4 VDI creates 20 inodes). It harms
> performance of recovery process. And exhaustion of VID space will come
> early.
> 
> Signed-off-by: Hitoshi Mitake <mitake.hitoshi at lab.ntt.co.jp>
> ---
>  dog/vdi.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 49 insertions(+), 1 deletion(-)
> 
> v2:
>  - use conventional style for has_own_objects()
>  - enhance commit log
> 
> diff --git a/dog/vdi.c b/dog/vdi.c
> index 66f2801..aa6c38d 100644
> --- a/dog/vdi.c
> +++ b/dog/vdi.c
> @@ -40,6 +40,8 @@ static struct sd_option vdi_options[] = {
>  	 "                          neither comparing nor repairing"},
>  	{'z', "block_size_shift", true, "specify the bit shift num for"
>  			       " data object size"},
> +	{'R', "reduce-identical-snapshots", false, "do not create snapshot if "
> +	 "working VDI doesn't have its own objects"},
>  	{ 0, NULL, false, NULL },
>  };
>  
> @@ -61,6 +63,7 @@ static struct vdi_cmd_data {
>  	uint64_t oid;
>  	bool no_share;
>  	bool exist;
> +	bool reduce_identical_snapshots;
>  } vdi_cmd_data = { ~0, };
>  
>  struct get_vdi_info {
> @@ -606,6 +609,32 @@ fail:
>  	return NULL;
>  }
>  
> +static int has_own_objects(uint32_t vid, bool *result)
> +{
> +	struct sd_inode *inode;
> +	int ret = SD_RES_SUCCESS;
> +
> +	*result = true;
> +	inode = xzalloc(sizeof(*inode));
> +
> +	ret = dog_read_object(vid_to_vdi_oid(vid), inode,
> +			      sizeof(*inode), 0, true);
> +	if (ret != SD_RES_SUCCESS)
> +		goto out;
> +
> +	for (int i = 0; i < SD_INODE_DATA_INDEX; i++) {
> +		if (inode->data_vdi_id[i] && inode->data_vdi_id[i] == vid)
> +			/* VDI has its own object */
> +			goto out;
> +	}
> +
> +	*result = false;
> +
> +out:
> +	free(inode);
> +	return ret;
> +}
> +
>  static int vdi_snapshot(int argc, char **argv)
>  {
>  	const char *vdiname = argv[optind++];
> @@ -704,6 +733,23 @@ static int vdi_snapshot(int argc, char **argv)
>  		nr_issued_prevent_inode_update++;
>  	}
>  
> +	if (vdi_cmd_data.reduce_identical_snapshots) {
> +		bool result;
> +		ret = has_own_objects(vid, &result);
> +
> +		if (ret != SD_RES_SUCCESS)
> +			goto out;
> +
> +		if (!result) {
> +			if (verbose)
> +				sd_info("VDI %s doesn't have its own objects, "
> +					"skipping creation of snapshot",
> +					vdiname);
> +
> +			goto out;
> +		}
> +	}
> +
>  	ret = dog_write_object(vid_to_vdi_oid(vid), 0,
>  			       vdi_cmd_data.snapshot_tag,
>  			       SD_MAX_VDI_TAG_LEN,
> @@ -3066,7 +3112,7 @@ static struct subcommand vdi_cmd[] = {
>  	{"create", "<vdiname> <size>", "PycaphrvzT", "create an image",
>  	 NULL, CMD_NEED_NODELIST|CMD_NEED_ARG,
>  	 vdi_create, vdi_options},
> -	{"snapshot", "<vdiname>", "saphrvT", "create a snapshot",
> +	{"snapshot", "<vdiname>", "saphrvTR", "create a snapshot",
>  	 NULL, CMD_NEED_ARG,
>  	 vdi_snapshot, vdi_options},
>  	{"clone", "<src vdi> <dst vdi>", "sPnaphrvT", "clone an image",
> @@ -3231,6 +3277,8 @@ static int vdi_parser(int ch, const char *opt)
>  		}
>  		vdi_cmd_data.block_size_shift = block_size_shift;
>  		break;
> +	case 'R':
> +		vdi_cmd_data.reduce_identical_snapshots = true;
>  	}
>  
>  	return 0;
> -- 
> 1.9.1
> 
> -- 
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Applied thanks

Yuan