From: Shenghui Wang <[email protected]>
We have the following define for btree iterator:
struct btree_iter {
size_t size, used;
#ifdef CONFIG_BCACHE_DEBUG
struct btree_keys *b;
#endif
struct btree_iter_set {
struct bkey *k, *end;
} data[MAX_BSETS];
};
We can see that the length of data[] field is static MAX_BSETS, which is
defined as 4 currently.
But a btree node on disk could have too many bsets for an iterator to fit
on the stack - maybe far more that MAX_BSETS. Have to dynamically allocate
space to host more btree_iter_sets.
bch_cache_set_alloc() will make sure the pool cache_set->fill_iter can
allocate an iterator equipped with enough room that can host
(sb.bucket_size / sb.block_size)
btree_iter_sets, which is more than static MAX_BSETS.
bch_btree_node_read_done() will use that pool to allocate one iterator, to
host many bsets in one btree node.
Add more comment around cache_set->fill_iter to make code less confusing.
Signed-off-by: Shenghui Wang <[email protected]>
Signed-off-by: Coly Li <[email protected]>
---
drivers/md/bcache/bcache.h | 6 +++++-
drivers/md/bcache/btree.c | 5 +++++
2 files changed, 10 insertions(+), 1 deletion(-)
diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index b61b83bbcfff..96d2213f279e 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -658,7 +658,11 @@ struct cache_set {
/*
* A btree node on disk could have too many bsets for an iterator to fit
- * on the stack - have to dynamically allocate them
+ * on the stack - have to dynamically allocate them.
+ * bch_cache_set_alloc() will make sure the pool can allocate iterators
+ * equipped with enough room that can host
+ * (sb.bucket_size / sb.block_size)
+ * btree_iter_sets, which is more than static MAX_BSETS.
*/
mempool_t fill_iter;
diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index 3f4211b5cd33..23cb1dc7296b 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -207,6 +207,11 @@ void bch_btree_node_read_done(struct btree *b)
struct bset *i = btree_bset_first(b);
struct btree_iter *iter;
+ /*
+ * c->fill_iter can allocate an iterator with more memory space
+ * than static MAX_BSETS.
+ * See the comment arount cache_set->fill_iter.
+ */
iter = mempool_alloc(&b->c->fill_iter, GFP_NOIO);
iter->size = b->c->sb.bucket_size / b->c->sb.block_size;
iter->used = 0;
--
2.16.4
