bcache: reap from tail of c->btree_cache in bch_mca_scan()

When shrink btree node cache from c->btree_cache in bch_mca_scan(),
no matter the selected node is reaped or not, it will be rotated from
the head to the tail of c->btree_cache list. But in bcache journal
code, when flushing the btree nodes with oldest journal entry, btree
nodes are iterated and slected from the tail of c->btree_cache list in
btree_flush_write(). The list_rotate_left() in bch_mca_scan() will
make btree_flush_write() iterate more nodes in c->btree_list in reverse
order.

This patch just reaps the selected btree node cache, and not move it
from the head to the tail of c->btree_cache list. Then bch_mca_scan()
will not mess up c->btree_cache list to btree_flush_write().

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 c3a314deb09d7c35c0617cbcb1bce7ef1b9f2f46..fa872df4e7703fb65b229c2ddcac9dbadad6593c 100644 (file)
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -747,19 +747,19 @@ static unsigned long bch_mca_scan(struct shrinker *shrink,
                i++;
        }
 
-       for (;  (nr--) && i < btree_cache_used; i++) {
-               if (list_empty(&c->btree_cache))
+       list_for_each_entry_safe_reverse(b, t, &c->btree_cache, list) {
+               if (nr <= 0 || i >= btree_cache_used)
                        goto out;
 
-               b = list_first_entry(&c->btree_cache, struct btree, list);
-               list_rotate_left(&c->btree_cache);
-
                if (!mca_reap(b, 0, false)) {
                        mca_bucket_free(b);
                        mca_data_free(b);
                        rw_unlock(true, b);
                        freed++;
                }
+
+               nr--;
+               i++;
        }
 out:
        mutex_unlock(&c->bucket_lock);