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

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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@xxxxxxx>
---
  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@xxxxxxx                               +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer



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