Function bch_btree_keys_init() initializes b->set[].size and
b->set[].data to zero. As the code comments indicates, these code indeed
is unncessary, because both struct btree_keys and struct bset_tree are
nested embedded into struct btree, when struct btree is filled with 0
bits by kzalloc() in mca_bucket_alloc(), b->set[].size and
b->set[].data are initialized to 0 (a.k.a NULL) already.

This patch removes the redundant code, and add comments in
bch_btree_keys_init() and mca_bucket_alloc() to explain why it's safe.

Signed-off-by: Coly Li <col...@suse.de>
---
 drivers/md/bcache/bset.c  | 13 ++++++-------
 drivers/md/bcache/btree.c |  4 ++++
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/drivers/md/bcache/bset.c b/drivers/md/bcache/bset.c
index 579c696a5fe0..343f4e9428e0 100644
--- a/drivers/md/bcache/bset.c
+++ b/drivers/md/bcache/bset.c
@@ -352,15 +352,14 @@ void bch_btree_keys_init(struct btree_keys *b, const 
struct btree_keys_ops *ops,
        b->nsets = 0;
        b->last_set_unwritten = 0;
 
-       /* XXX: shouldn't be needed */
-       for (i = 0; i < MAX_BSETS; i++)
-               b->set[i].size = 0;
        /*
-        * Second loop starts at 1 because b->keys[0]->data is the memory we
-        * allocated
+        * struct btree_keys in embedded in struct btree, and struct
+        * bset_tree is embedded into struct btree_keys. They are all
+        * initialized as 0 by kzalloc() in mca_bucket_alloc(), and
+        * b->set[0].data is allocated in bch_btree_keys_alloc(), so we
+        * don't have to initiate b->set[].size and b->set[].data here
+        * any more.
         */
-       for (i = 1; i < MAX_BSETS; i++)
-               b->set[i].data = NULL;
 }
 EXPORT_SYMBOL(bch_btree_keys_init);
 
diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index 17936b2dc7d6..344641e23415 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -600,6 +600,10 @@ static void mca_data_alloc(struct btree *b, struct bkey 
*k, gfp_t gfp)
 static struct btree *mca_bucket_alloc(struct cache_set *c,
                                      struct bkey *k, gfp_t gfp)
 {
+       /*
+        * kzalloc() is necessary here for initialization,
+        * see code comments in bch_btree_keys_init().
+        */
        struct btree *b = kzalloc(sizeof(struct btree), gfp);
        if (!b)
                return NULL;
-- 
2.16.2

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