1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index a6ad49ac5f2b..04636a70ffaa 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -622,6 +622,13 @@ static int bch_mca_shrink(struct shrinker *shrink, struct shrink_control *sc)
         else if (!mutex_trylock(&c->bucket_lock))
                 return -1;
 
+        /*
+         * It's _really_ critical that we don't free too many btree nodes - we
+         * have to always leave ourselves a reserve. The reserve is how we
+         * guarantee that allocating memory for a new btree node can always
+         * succeed, so that inserting keys into the btree can always succeed and
+         * IO can always make forward progress:
+         */
         nr /= c->btree_pages;
         nr = min_t(unsigned long, nr, mca_can_free(c));