Hi Coly,
>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.
>
Eh, you need to pay attention to mca_alloc()==>mca_reap(),
which get btree node memory from list btree_cache_freeable
or btree_cache_freed, that merory were used as btree node before,
and may be not fill with 0.
>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 <colyli@xxxxxxx>
>---
> 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
Thanks.
Tang Junhui
