From 89b1fc54c257104df007c5888e3705e52b973d45 Mon Sep 17 00:00:00 2001
From: Tang Junhui <tang.junhui@zte.com.cn>
Date: Wed, 6 Sep 2017 14:25:58 +0800
Subject: [PATCH] bcache: increase the number of open buckets
Git-commit: 89b1fc54c257104df007c5888e3705e52b973d45
Patch-mainline: v4.14-rc1
References: bsc#1076110

In currently, we only alloc 6 open buckets for each cache set,
but in usually, we always attach about 10 or so backend devices for
each cache set, and the each bcache device are always accessed by
about 10 or so threads in top application layer. So 6 open buckets
are too few, It has led to that each of the same thread write data
to different buckets, which would cause low efficiency write-back,
and also cause buckets inefficient, and would be Very easy to run
out of.

I add debug message in bch_open_buckets_alloc() to print alloc bucket
info, and test with ten bcache devices with a cache set, and each
bcache device is accessed by ten threads.

From the debug message, we can see that, after the modification, One
bucket is more likely to assign to the same thread, and the data from
the same thread are more likely to write the same bucket. Usually the
same thread always write/read the same backend device, so it is good
for write-back and also promote the usage efficiency of buckets.

Signed-off-by: Tang Junhui <tang.junhui@zte.com.cn>
Reviewed-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Coly Li <colyli@suse.de>

---
 drivers/md/bcache/alloc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c
index ca4abe1ccd8d..cacbe2dbd5c3 100644
--- a/drivers/md/bcache/alloc.c
+++ b/drivers/md/bcache/alloc.c
@@ -68,6 +68,8 @@
 #include <linux/random.h>
 #include <trace/events/bcache.h>
 
+#define MAX_OPEN_BUCKETS 128
+
 /* Bucket heap / gen */
 
 uint8_t bch_inc_gen(struct cache *ca, struct bucket *b)
@@ -671,7 +673,7 @@ int bch_open_buckets_alloc(struct cache_set *c)
 
 	spin_lock_init(&c->data_bucket_lock);
 
-	for (i = 0; i < 6; i++) {
+	for (i = 0; i < MAX_OPEN_BUCKETS; i++) {
 		struct open_bucket *b = kzalloc(sizeof(*b), GFP_KERNEL);
 		if (!b)
 			return -ENOMEM;
-- 
2.15.1