From c2e8dcf7fa43ed236cb341c33aa3a75687557c43 Mon Sep 17 00:00:00 2001
From: Coly Li <colyli@suse.de>
Date: Thu, 9 Aug 2018 15:48:44 +0800
Subject: [PATCH] bcache: avoid unncessary cache prefetch bch_btree_node_get()
Git-commit: c2e8dcf7fa43ed236cb341c33aa3a75687557c43
References: bsc#1064232
Patch-mainline: v4.19-rc1

In bch_btree_node_get() the read-in btree node will be partially
prefetched into L1 cache for following bset iteration (if there is).
But if the btree node read is failed, the perfetch operations will
waste L1 cache space. This patch checkes whether read operation and
only does cache prefetch when read I/O succeeded.

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

---
 drivers/md/bcache/btree.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index 475008fbbaab..c19f7716df88 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -1011,6 +1011,13 @@ struct btree *bch_btree_node_get(struct cache_set *c, struct btree_op *op,
 		BUG_ON(b->level != level);
 	}
 
+	if (btree_node_io_error(b)) {
+		rw_unlock(write, b);
+		return ERR_PTR(-EIO);
+	}
+
+	BUG_ON(!b->written);
+
 	b->parent = parent;
 	b->accessed = 1;
 
@@ -1022,13 +1029,6 @@ struct btree *bch_btree_node_get(struct cache_set *c, struct btree_op *op,
 	for (; i <= b->keys.nsets; i++)
 		prefetch(b->keys.set[i].data);
 
-	if (btree_node_io_error(b)) {
-		rw_unlock(write, b);
-		return ERR_PTR(-EIO);
-	}
-
-	BUG_ON(!b->written);
-
 	return b;
 }
 
-- 
2.16.4