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authorShenghui Wang <shhuiw@foxmail.com>2018-12-13 22:53:46 +0800
committerJens Axboe <axboe@kernel.dk>2018-12-13 08:15:54 -0700
commitd2f96f487f471b4c718324ecd1540c89d2be52ac (patch)
treee4614454eb5e8836a43553696c1cacae83ad24a2
parent0273ac349f08f4ff9ef88aaaf9c9f2aa6e87d2be (diff)
downloadlinux-d2f96f487f471b4c718324ecd1540c89d2be52ac.tar.bz2
bcache: add comment for cache_set->fill_iter
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 <shhuiw@foxmail.com> Signed-off-by: Coly Li <colyli@suse.de> Signed-off-by: Jens Axboe <axboe@kernel.dk>
-rw-r--r--drivers/md/bcache/bcache.h6
-rw-r--r--drivers/md/bcache/btree.c5
2 files changed, 10 insertions, 1 deletions
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;