Re: [PATCH 03/12] dm-zoned: use on-stack superblock for tertiary devices

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On 2020/05/23 0:39, Hannes Reinecke wrote:
> Checking the teriary superblock just consists of validating UUIDs,

s/teriary/tertiary

> crcs, and the generation number; it doesn't have contents which
> would be required during the actual operation.
> So we should use an on-stack superblock and avoid having to store
> it together with the 'real' superblocks.

...a temoprary in-memory superblock allocation...

The entire structure should not be on stack... see below.

> 
> Signed-off-by: Hannes Reinecke <hare@xxxxxxx>
> ---
>  drivers/md/dm-zoned-metadata.c | 98 +++++++++++++++++++++++-------------------
>  1 file changed, 53 insertions(+), 45 deletions(-)
> 
> diff --git a/drivers/md/dm-zoned-metadata.c b/drivers/md/dm-zoned-metadata.c
> index 3da6702bb1ae..b70a988fa771 100644
> --- a/drivers/md/dm-zoned-metadata.c
> +++ b/drivers/md/dm-zoned-metadata.c
> @@ -174,7 +174,7 @@ struct dmz_metadata {
>  	/* Zone information array */
>  	struct xarray		zones;
>  
> -	struct dmz_sb		sb[3];
> +	struct dmz_sb		sb[2];
>  	unsigned int		mblk_primary;
>  	unsigned int		sb_version;
>  	u64			sb_gen;
> @@ -995,10 +995,11 @@ int dmz_flush_metadata(struct dmz_metadata *zmd)
>  /*
>   * Check super block.
>   */
> -static int dmz_check_sb(struct dmz_metadata *zmd, unsigned int set)
> +static int dmz_check_sb(struct dmz_metadata *zmd, struct dmz_sb *dsb,
> +			bool tertiary)
>  {
> -	struct dmz_super *sb = zmd->sb[set].sb;
> -	struct dmz_dev *dev = zmd->sb[set].dev;
> +	struct dmz_super *sb = dsb->sb;
> +	struct dmz_dev *dev = dsb->dev;
>  	unsigned int nr_meta_zones, nr_data_zones;
>  	u32 crc, stored_crc;
>  	u64 gen;
> @@ -1015,7 +1016,7 @@ static int dmz_check_sb(struct dmz_metadata *zmd, unsigned int set)
>  			    DMZ_META_VER, zmd->sb_version);
>  		return -EINVAL;
>  	}
> -	if ((zmd->sb_version < 1) && (set == 2)) {
> +	if ((zmd->sb_version < 1) && tertiary) {
>  		dmz_dev_err(dev, "Tertiary superblocks are not supported");
>  		return -EINVAL;
>  	}
> @@ -1059,7 +1060,7 @@ static int dmz_check_sb(struct dmz_metadata *zmd, unsigned int set)
>  			return -ENXIO;
>  		}
>  
> -		if (set == 2) {
> +		if (tertiary) {
>  			/*
>  			 * Generation number should be 0, but it doesn't
>  			 * really matter if it isn't.
> @@ -1108,13 +1109,13 @@ static int dmz_check_sb(struct dmz_metadata *zmd, unsigned int set)
>  /*
>   * Read the first or second super block from disk.
>   */
> -static int dmz_read_sb(struct dmz_metadata *zmd, unsigned int set)
> +static int dmz_read_sb(struct dmz_metadata *zmd, struct dmz_sb *sb, int set)
>  {
>  	DMDEBUG("(%s): read superblock set %d dev %s block %llu",
>  		zmd->devname, set, zmd->sb[set].dev->name,
>  		zmd->sb[set].block);
> -	return dmz_rdwr_block(zmd->sb[set].dev, REQ_OP_READ,
> -			      zmd->sb[set].block, zmd->sb[set].mblk->page);
> +	return dmz_rdwr_block(sb->dev, REQ_OP_READ,
> +			      sb->block, sb->mblk->page);
>  }
>  
>  /*
> @@ -1142,7 +1143,7 @@ static int dmz_lookup_secondary_sb(struct dmz_metadata *zmd)
>  	zmd->sb[1].zone = xa_load(&zmd->zones, zone_id + 1);
>  	zmd->sb[1].dev = dmz_zone_to_dev(zmd, zmd->sb[1].zone);
>  	for (i = 1; i < zmd->nr_rnd_zones; i++) {
> -		if (dmz_read_sb(zmd, 1) != 0)
> +		if (dmz_read_sb(zmd, &zmd->sb[1], 1) != 0)
>  			break;
>  		if (le32_to_cpu(zmd->sb[1].sb->magic) == DMZ_MAGIC)
>  			return 0;
> @@ -1160,9 +1161,9 @@ static int dmz_lookup_secondary_sb(struct dmz_metadata *zmd)
>  }
>  
>  /*
> - * Read the first or second super block from disk.
> + * Read a super block from disk.
>   */
> -static int dmz_get_sb(struct dmz_metadata *zmd, unsigned int set)
> +static int dmz_get_sb(struct dmz_metadata *zmd, struct dmz_sb *sb, int set)
>  {
>  	struct dmz_mblock *mblk;
>  	int ret;
> @@ -1172,14 +1173,14 @@ static int dmz_get_sb(struct dmz_metadata *zmd, unsigned int set)
>  	if (!mblk)
>  		return -ENOMEM;
>  
> -	zmd->sb[set].mblk = mblk;
> -	zmd->sb[set].sb = mblk->data;
> +	sb->mblk = mblk;
> +	sb->sb = mblk->data;
>  
>  	/* Read super block */
> -	ret = dmz_read_sb(zmd, set);
> +	ret = dmz_read_sb(zmd, sb, set);
>  	if (ret) {
>  		dmz_free_mblock(zmd, mblk);
> -		zmd->sb[set].mblk = NULL;
> +		sb->mblk = NULL;
>  		return ret;
>  	}
>  
> @@ -1253,13 +1254,13 @@ static int dmz_load_sb(struct dmz_metadata *zmd)
>  	/* Read and check the primary super block */
>  	zmd->sb[0].block = dmz_start_block(zmd, zmd->sb[0].zone);
>  	zmd->sb[0].dev = dmz_zone_to_dev(zmd, zmd->sb[0].zone);
> -	ret = dmz_get_sb(zmd, 0);
> +	ret = dmz_get_sb(zmd, &zmd->sb[0], 0);
>  	if (ret) {
>  		dmz_dev_err(zmd->sb[0].dev, "Read primary super block failed");
>  		return ret;
>  	}
>  
> -	ret = dmz_check_sb(zmd, 0);
> +	ret = dmz_check_sb(zmd, &zmd->sb[0], false);
>  
>  	/* Read and check secondary super block */
>  	if (ret == 0) {
> @@ -1272,7 +1273,7 @@ static int dmz_load_sb(struct dmz_metadata *zmd)
>  		}
>  		zmd->sb[1].block = dmz_start_block(zmd, zmd->sb[1].zone);
>  		zmd->sb[1].dev = dmz_zone_to_dev(zmd, zmd->sb[1].zone);
> -		ret = dmz_get_sb(zmd, 1);
> +		ret = dmz_get_sb(zmd, &zmd->sb[1], 1);
>  	} else
>  		ret = dmz_lookup_secondary_sb(zmd);
>  
> @@ -1281,7 +1282,7 @@ static int dmz_load_sb(struct dmz_metadata *zmd)
>  		return ret;
>  	}
>  
> -	ret = dmz_check_sb(zmd, 1);
> +	ret = dmz_check_sb(zmd, &zmd->sb[1], false);
>  	if (ret == 0)
>  		sb_good[1] = true;
>  
> @@ -1326,18 +1327,32 @@ static int dmz_load_sb(struct dmz_metadata *zmd)
>  		      "Using super block %u (gen %llu)",
>  		      zmd->mblk_primary, zmd->sb_gen);
>  
> -	if ((zmd->sb_version > 1) && zmd->sb[2].zone) {
> -		zmd->sb[2].block = dmz_start_block(zmd, zmd->sb[2].zone);
> -		zmd->sb[2].dev = dmz_zone_to_dev(zmd, zmd->sb[2].zone);
> -		ret = dmz_get_sb(zmd, 2);
> -		if (ret) {
> -			dmz_dev_err(zmd->sb[2].dev,
> -				    "Read tertiary super block failed");
> -			return ret;
> +	if (zmd->sb_version > 1) {
> +		int i;
> +
> +		for (i = 1; i < zmd->nr_devs; i++) {
> +			struct dmz_sb sb;

I would rather have dmz_get_sb() allocate this struct than have it on stack...
It is not big, but still. To be symetric, we can add dmz_put_sb() for freeing it.

> +
> +			sb.block = 0;
> +			sb.zone = dmz_get(zmd, zmd->dev[i].zone_offset);
> +			sb.dev = &zmd->dev[i];
> +			if (!dmz_is_meta(sb.zone)) {
> +				dmz_dev_err(sb.dev,
> +					    "Tertiary super block zone %u not marked as metadata zone",
> +					    sb.zone->id);
> +				return -EINVAL;
> +			}
> +			ret = dmz_get_sb(zmd, &sb, i + 1);
> +			if (ret) {
> +				dmz_dev_err(sb.dev,
> +					    "Read tertiary super block failed");
> +				return ret;
> +			}
> +			ret = dmz_check_sb(zmd, &sb, true);
> +			dmz_free_mblock(zmd, sb.mblk);
> +			if (ret == -EINVAL)
> +				return ret;
>  		}
> -		ret = dmz_check_sb(zmd, 2);
> -		if (ret == -EINVAL)
> -			return ret;
>  	}
>  	return 0;
>  }
> @@ -1402,12 +1417,15 @@ static int dmz_init_zone(struct blk_zone *blkz, unsigned int num, void *data)
>  				zmd->sb[0].zone = zone;
>  			}
>  		}
> -		if (zmd->nr_devs > 1 && !zmd->sb[2].zone) {
> -			/* Tertiary superblock zone */
> -			zmd->sb[2].zone = zone;
> +		if (zmd->nr_devs > 1 && num == 0) {
> +			/*
> +			 * Tertiary superblock zones are always at the
> +			 * start of the zoned devices, so mark them
> +			 * as metadata zone.
> +			 */
> +			set_bit(DMZ_META, &zone->flags);
>  		}
>  	}
> -
>  	return 0;
>  }
>  
> @@ -2850,16 +2868,6 @@ int dmz_ctr_metadata(struct dmz_dev *dev, int num_dev,
>  		}
>  		set_bit(DMZ_META, &zone->flags);
>  	}
> -	if (zmd->sb[2].zone) {
> -		zone = dmz_get(zmd, zmd->sb[2].zone->id);
> -		if (!zone) {
> -			dmz_zmd_err(zmd,
> -				    "Tertiary metadata zone not present");
> -			ret = -ENXIO;
> -			goto err;
> -		}
> -		set_bit(DMZ_META, &zone->flags);
> -	}
>  	/* Load mapping table */
>  	ret = dmz_load_mapping(zmd);
>  	if (ret)
> 


-- 
Damien Le Moal
Western Digital Research



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