bcache: make cutoff_writeback and cutoff_writeback_sync tunable

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>

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 61d3b63fa61721c860a166788886dcea64ed6c34..4dee119c36646a54a301aafa280bc3d9a6df27e5 100644 (file)
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -25,6 +25,9 @@
 #include <linux/reboot.h>
 #include <linux/sysfs.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
@@ -2420,6 +2423,32 @@ 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[] = {
@@ -2428,6 +2457,8 @@ static int __init bcache_init(void)
                NULL
        };
 
+       check_module_parameters();
+
        mutex_init(&bch_register_lock);
        init_waitqueue_head(&unregister_wait);
        register_reboot_notifier(&reboot);
@@ -2464,9 +2495,18 @@ 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");

diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
index 621186b4240faafd9746c4f4d3b54f2e99ee3a4e..482b128b3e9d8a6767134ba8e1f62ed02a5360c9 100644 (file)
--- a/drivers/md/bcache/sysfs.c
+++ b/drivers/md/bcache/sysfs.c
@@ -88,6 +88,8 @@ 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);
 
@@ -686,6 +688,9 @@ 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);
@@ -883,6 +888,8 @@ static struct attribute *bch_cache_set_internal_files[] = {
        &sysfs_copy_gc_enabled,
        &sysfs_gc_after_writeback,
        &sysfs_io_disable,
+       &sysfs_cutoff_writeback,
+       &sysfs_cutoff_writeback_sync,
        NULL
 };
 KTYPE(bch_cache_set_internal);

diff --git a/drivers/md/bcache/writeback.h b/drivers/md/bcache/writeback.h
index ce63be98a39d7586cf2e003041e7dc9bc4e841a9..6a743d3bb3389472ce054ff11de1b00bda97e717 100644 (file)
--- a/drivers/md/bcache/writeback.h
+++ b/drivers/md/bcache/writeback.h
@@ -5,6 +5,9 @@
 #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 */
 
@@ -55,6 +58,9 @@ static inline bool bcache_dev_stripe_dirty(struct cached_dev *dc,
        }
 }
 
+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)
 {
@@ -62,7 +68,7 @@ static inline bool should_writeback(struct cached_dev *dc, struct bio *bio,
 
        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 &&
@@ -75,7 +81,7 @@ static inline bool should_writeback(struct cached_dev *dc, struct bio *bio,
 
        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)