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

[Coly Li <colyli@suse.de>]

On 2020/8/17 14:22, Hannes Reinecke wrote:
> 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.

Sure, I will do it in next version series.

Thanks.

Coly Li