bcache: add code comments in bch_btree_leaf_dirty()

This patch adds code comments in bch_btree_leaf_dirty() to explain
why w->journal should always reference the eldest journal pin of
all the writing bkeys in the btree node. To make the bcache journal
code to be easier to be understood.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index 39d7fc1ef1eeb87ad6938eb30b6084e9c46cd6ec..48e33ee0d8761a915ed7e3749c797135d0c2d66b 100644 (file)
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -569,6 +569,11 @@ static void bch_btree_leaf_dirty(struct btree *b, atomic_t *journal_ref)
 
        set_btree_node_dirty(b);
 
+       /*
+        * w->journal is always the oldest journal pin of all bkeys
+        * in the leaf node, to make sure the oldest jset seq won't
+        * be increased before this btree node is flushed.
+        */
        if (journal_ref) {
                if (w->journal &&
                    journal_pin_cmp(b->c, w->journal, journal_ref)) {