Re: [PATCH 09/14] bcache: avoid data copy between cache_set->sb and cache->sb

[Hannes Reinecke <hare@suse.de>]

On 8/15/20 6:10 AM, Coly Li wrote:
> struct cache_sb embedded in struct cache_set is only partial used and
> not a real copy from cache's in-memory super block. When removing the
> embedded cache_set->sb, it is unncessary to copy data between these two
> in-memory super blocks (cache_set->sb and cache->sb), it is sufficient
> to just use cache->sb.
> 
> This patch removes the data copy between these two in-memory super
> blocks in bch_cache_set_alloc() and bcache_write_super(). In future
> except for set_uuid, cache's super block will be referenced by cache
> set, no copy any more.
> 
> Signed-off-by: Coly Li <colyli@suse.de>
> ---
>   drivers/md/bcache/super.c | 22 +++-------------------
>   1 file changed, 3 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index 748b08ab4f11..05c5a7e867bb 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -350,16 +350,10 @@ void bcache_write_super(struct cache_set *c)
>   	down(&c->sb_write_mutex);
>   	closure_init(cl, &c->cl);
>   
> -	c->sb.seq++;
> +	ca->sb.seq++;
>   
> -	if (c->sb.version > version)
> -		version = c->sb.version;
> -
> -	ca->sb.version		= version;
> -	ca->sb.seq		= c->sb.seq;
> -	ca->sb.last_mount	= c->sb.last_mount;
> -
> -	SET_CACHE_SYNC(&ca->sb, CACHE_SYNC(&c->sb));
> +	if (ca->sb.version < version)
> +		ca->sb.version = version;
>   
>   	bio_init(bio, ca->sb_bv, 1);
>   	bio_set_dev(bio, ca->bdev);
> @@ -1860,16 +1854,6 @@ struct cache_set *bch_cache_set_alloc(struct cache_sb *sb)
>   	bch_cache_accounting_init(&c->accounting, &c->cl);
>   
>   	memcpy(c->set_uuid, sb->set_uuid, 16);
> -	c->sb.block_size	= sb->block_size;
> -	c->sb.bucket_size	= sb->bucket_size;
> -	c->sb.nr_in_set		= sb->nr_in_set;
> -	c->sb.last_mount	= sb->last_mount;
> -	c->sb.version		= sb->version;
> -	if (c->sb.version >= BCACHE_SB_VERSION_CDEV_WITH_FEATURES) {
> -		c->sb.feature_compat = sb->feature_compat;
> -		c->sb.feature_ro_compat = sb->feature_ro_compat;
> -		c->sb.feature_incompat = sb->feature_incompat;
> -	}
>   
>   	c->bucket_bits		= ilog2(sb->bucket_size);
>   	c->block_bits		= ilog2(sb->block_size);
> 
Please fold it into patch 13, as then it's obvious why we don't need 
this copy actions anymore.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke            Teamlead Storage & Networking
hare@suse.de                               +49 911 74053 688
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