From 9aaf51654672b16566c5fe787da3ca41ebf6d297 Mon Sep 17 00:00:00 2001
From: Coly Li <colyli@suse.de>
Date: Thu, 13 Dec 2018 22:53:55 +0800
Subject: [PATCH] bcache: make cutoff_writeback and cutoff_writeback_sync
tunable
Git-commit: 9aaf51654672b16566c5fe787da3ca41ebf6d297
Patch-mainline: v5.0-rc1
References: bsc#1130972
Currently the cutoff writeback and cutoff writeback sync thresholds are
defined by CUTOFF_WRITEBACK (40) and CUTOFF_WRITEBACK_SYNC (70) as
static values. Most of time these they work fine, but when people want
to do research on bcache writeback mode performance tuning, there is no
chance to modify the soft and hard cutoff writeback values.
This patch introduces two module parameters bch_cutoff_writeback_sync
and bch_cutoff_writeback which permit people to tune the values when
loading bcache.ko. If they are not specified by module loading, current
values CUTOFF_WRITEBACK_SYNC and CUTOFF_WRITEBACK will be used as
default and nothing changes.
When people want to tune this two values,
- cutoff_writeback can be set in range [1, 70]
- cutoff_writeback_sync can be set in range [1, 90]
- cutoff_writeback always <= cutoff_writeback_sync
The default values are strongly recommended to most of users for most of
workloads. Anyway, if people wants to take their own risk to do research
on new writeback cutoff tuning for their own workload, now they can make
it.
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
drivers/md/bcache/super.c | 40 ++++++++++++++++++++++++++++++++++++++++
drivers/md/bcache/sysfs.c | 7 +++++++
drivers/md/bcache/writeback.h | 10 ++++++++--
3 files changed, 55 insertions(+), 2 deletions(-)
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -26,6 +26,9 @@
#include <linux/sysfs.h>
#include <linux/overflow.h>
+unsigned int bch_cutoff_writeback;
+unsigned int bch_cutoff_writeback_sync;
+
static const char bcache_magic[] = {
0xc6, 0x85, 0x73, 0xf6, 0x4e, 0x1a, 0x45, 0xca,
0x82, 0x65, 0xf5, 0x7f, 0x48, 0xba, 0x6d, 0x81
@@ -2432,6 +2435,32 @@ static void bcache_exit(void)
mutex_destroy(&bch_register_lock);
}
+/* Check and fixup module parameters */
+static void check_module_parameters(void)
+{
+ if (bch_cutoff_writeback_sync == 0)
+ bch_cutoff_writeback_sync = CUTOFF_WRITEBACK_SYNC;
+ else if (bch_cutoff_writeback_sync > CUTOFF_WRITEBACK_SYNC_MAX) {
+ pr_warn("set bch_cutoff_writeback_sync (%u) to max value %u",
+ bch_cutoff_writeback_sync, CUTOFF_WRITEBACK_SYNC_MAX);
+ bch_cutoff_writeback_sync = CUTOFF_WRITEBACK_SYNC_MAX;
+ }
+
+ if (bch_cutoff_writeback == 0)
+ bch_cutoff_writeback = CUTOFF_WRITEBACK;
+ else if (bch_cutoff_writeback > CUTOFF_WRITEBACK_MAX) {
+ pr_warn("set bch_cutoff_writeback (%u) to max value %u",
+ bch_cutoff_writeback, CUTOFF_WRITEBACK_MAX);
+ bch_cutoff_writeback = CUTOFF_WRITEBACK_MAX;
+ }
+
+ if (bch_cutoff_writeback > bch_cutoff_writeback_sync) {
+ pr_warn("set bch_cutoff_writeback (%u) to %u",
+ bch_cutoff_writeback, bch_cutoff_writeback_sync);
+ bch_cutoff_writeback = bch_cutoff_writeback_sync;
+ }
+}
+
static int __init bcache_init(void)
{
static const struct attribute *files[] = {
@@ -2440,6 +2469,8 @@ static int __init bcache_init(void)
NULL
};
+ check_module_parameters();
+
mutex_init(&bch_register_lock);
init_waitqueue_head(&unregister_wait);
register_reboot_notifier(&reboot);
@@ -2476,9 +2507,18 @@ err:
return -ENOMEM;
}
+/*
+ * Module hooks
+ */
module_exit(bcache_exit);
module_init(bcache_init);
+module_param(bch_cutoff_writeback, uint, 0);
+MODULE_PARM_DESC(bch_cutoff_writeback, "threshold to cutoff writeback");
+
+module_param(bch_cutoff_writeback_sync, uint, 0);
+MODULE_PARM_DESC(bch_cutoff_writeback_sync, "hard threshold to cutoff writeback");
+
MODULE_DESCRIPTION("Bcache: a Linux block layer cache");
MODULE_AUTHOR("Kent Overstreet <kent.overstreet@gmail.com>");
MODULE_LICENSE("GPL");
--- a/drivers/md/bcache/sysfs.c
+++ b/drivers/md/bcache/sysfs.c
@@ -87,6 +87,8 @@ read_attribute(writeback_keys_done);
read_attribute(writeback_keys_failed);
read_attribute(io_errors);
read_attribute(congested);
+read_attribute(cutoff_writeback);
+read_attribute(cutoff_writeback_sync);
rw_attribute(congested_read_threshold_us);
rw_attribute(congested_write_threshold_us);
@@ -685,6 +687,9 @@ SHOW(__bch_cache_set)
sysfs_print(congested_write_threshold_us,
c->congested_write_threshold_us);
+ sysfs_print(cutoff_writeback, bch_cutoff_writeback);
+ sysfs_print(cutoff_writeback_sync, bch_cutoff_writeback_sync);
+
sysfs_print(active_journal_entries, fifo_used(&c->journal.pin));
sysfs_printf(verify, "%i", c->verify);
sysfs_printf(key_merging_disabled, "%i", c->key_merging_disabled);
@@ -882,6 +887,8 @@ static struct attribute *bch_cache_set_i
&sysfs_copy_gc_enabled,
&sysfs_gc_after_writeback,
&sysfs_io_disable,
+ &sysfs_cutoff_writeback,
+ &sysfs_cutoff_writeback_sync,
NULL
};
KTYPE(bch_cache_set_internal);
--- a/drivers/md/bcache/writeback.h
+++ b/drivers/md/bcache/writeback.h
@@ -4,6 +4,9 @@
#define CUTOFF_WRITEBACK 40
#define CUTOFF_WRITEBACK_SYNC 70
+#define CUTOFF_WRITEBACK_MAX 70
+#define CUTOFF_WRITEBACK_SYNC_MAX 90
+
#define MAX_WRITEBACKS_IN_PASS 5
#define MAX_WRITESIZE_IN_PASS 5000 /* *512b */
@@ -54,6 +57,9 @@ static inline bool bcache_dev_stripe_dir
}
}
+extern unsigned int bch_cutoff_writeback;
+extern unsigned int bch_cutoff_writeback_sync;
+
static inline bool should_writeback(struct cached_dev *dc, struct bio *bio,
unsigned int cache_mode, bool would_skip)
{
@@ -61,7 +67,7 @@ static inline bool should_writeback(stru
if (cache_mode != CACHE_MODE_WRITEBACK ||
test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) ||
- in_use > CUTOFF_WRITEBACK_SYNC)
+ in_use > bch_cutoff_writeback_sync)
return false;
if (dc->partial_stripes_expensive &&
@@ -74,7 +80,7 @@ static inline bool should_writeback(stru
return (op_is_sync(bio->bi_opf) ||
bio->bi_opf & (REQ_META|REQ_PRIO) ||
- in_use <= CUTOFF_WRITEBACK);
+ in_use <= bch_cutoff_writeback);
}
static inline void bch_writeback_queue(struct cached_dev *dc)