bcache: Convert writeback to a kthread

This simplifies the writeback flow control quite a bit - previously, it
was conceptually two coroutines, refill_dirty() and read_dirty(). This
makes the code quite a bit more straightforward.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>

4 files changed, 203 insertions, 206 deletions

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 09410eb07d82..674e2f42e778 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -509,7 +509,7 @@ struct cached_dev {
 
         /* Limit number of writeback bios in flight */
         struct semaphore        in_flight;
-        struct closure_with_timer writeback;
+        struct task_struct      *writeback_thread;
 
         struct keybuf           writeback_keys;
 
@@ -1038,7 +1038,11 @@ static inline void bkey_init(struct bkey *k)
 
 #define KEY_START(k)            (KEY_OFFSET(k) - KEY_SIZE(k))
 #define START_KEY(k)            KEY(KEY_INODE(k), KEY_START(k), 0)
-#define MAX_KEY                 KEY(~(~0 << 20), ((uint64_t) ~0) >> 1, 0)
+
+#define MAX_KEY_INODE           (~(~0 << 20))
+#define MAX_KEY_OFFSET          (((uint64_t) ~0) >> 1)
+#define MAX_KEY                 KEY(MAX_KEY_INODE, MAX_KEY_OFFSET, 0)
+
 #define ZERO_KEY                KEY(0, 0, 0)
 
 /*
@@ -1214,8 +1218,6 @@ int bch_cache_allocator_init(struct cache *ca);
 
 void bch_debug_exit(void);
 int bch_debug_init(struct kobject *);
-void bch_writeback_exit(void);
-int bch_writeback_init(void);
 void bch_request_exit(void);
 int bch_request_init(void);
 void bch_btree_exit(void);
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index f89e2296bde1..b79dd5a6679e 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1029,6 +1029,7 @@ static void cached_dev_free(struct closure *cl)
         struct cached_dev *dc = container_of(cl, struct cached_dev, disk.cl);
 
         cancel_delayed_work_sync(&dc->writeback_rate_update);
+        kthread_stop(dc->writeback_thread);
 
         mutex_lock(&bch_register_lock);
 
@@ -2006,7 +2007,6 @@ static struct notifier_block reboot = {
 static void bcache_exit(void)
 {
         bch_debug_exit();
-        bch_writeback_exit();
         bch_request_exit();
         bch_btree_exit();
         if (bcache_kobj)
@@ -2039,7 +2039,6 @@ static int __init bcache_init(void)
             sysfs_create_files(bcache_kobj, files) ||
             bch_btree_init() ||
             bch_request_init() ||
-            bch_writeback_init() ||
             bch_debug_init(bcache_kobj))
                 goto err;
 
diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index 51dc709c9bf7..4392f3f38d62 100644
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -11,18 +11,11 @@
 #include "debug.h"
 #include "writeback.h"
 
+#include <linux/delay.h>
+#include <linux/freezer.h>
+#include <linux/kthread.h>
 #include <trace/events/bcache.h>
 
-static struct workqueue_struct *dirty_wq;
-
-static void read_dirty(struct closure *);
-
-struct dirty_io {
-        struct closure          cl;
-        struct cached_dev       *dc;
-        struct bio              bio;
-};
-
 /* Rate limiting */
 
 static void __update_writeback_rate(struct cached_dev *dc)
@@ -72,9 +65,6 @@ out:
         dc->writeback_rate_derivative = derivative;
         dc->writeback_rate_change = change;
         dc->writeback_rate_target = target;
-
-        schedule_delayed_work(&dc->writeback_rate_update,
-                              dc->writeback_rate_update_seconds * HZ);
 }
 
 static void update_writeback_rate(struct work_struct *work)
@@ -90,6 +80,9 @@ static void update_writeback_rate(struct work_struct *work)
                 __update_writeback_rate(dc);
 
         up_read(&dc->writeback_lock);
+
+        schedule_delayed_work(&dc->writeback_rate_update,
+                              dc->writeback_rate_update_seconds * HZ);
 }
 
 static unsigned writeback_delay(struct cached_dev *dc, unsigned sectors)
@@ -105,37 +98,11 @@ static unsigned writeback_delay(struct cached_dev *dc, unsigned sectors)
         return min_t(uint64_t, ret, HZ);
 }
 
-/* Background writeback */
-
-static bool dirty_pred(struct keybuf *buf, struct bkey *k)
-{
-        return KEY_DIRTY(k);
-}
-
-static bool dirty_full_stripe_pred(struct keybuf *buf, struct bkey *k)
-{
-        uint64_t stripe = KEY_START(k);
-        unsigned nr_sectors = KEY_SIZE(k);
-        struct cached_dev *dc = container_of(buf, struct cached_dev,
-                                             writeback_keys);
-
-        if (!KEY_DIRTY(k))
-                return false;
-
-        do_div(stripe, dc->disk.stripe_size);
-
-        while (1) {
-                if (atomic_read(dc->disk.stripe_sectors_dirty + stripe) ==
-                    dc->disk.stripe_size)
-                        return true;
-
-                if (nr_sectors <= dc->disk.stripe_size)
-                        return false;
-
-                nr_sectors -= dc->disk.stripe_size;
-                stripe++;
-        }
-}
+struct dirty_io {
+        struct closure          cl;
+        struct cached_dev       *dc;
+        struct bio              bio;
+};
 
 static void dirty_init(struct keybuf_key *w)
 {
@@ -153,132 +120,6 @@ static void dirty_init(struct keybuf_key *w)
         bch_bio_map(bio, NULL);
 }
 
-static void refill_dirty(struct closure *cl)
-{
-        struct cached_dev *dc = container_of(cl, struct cached_dev,
-                                             writeback.cl);
-        struct keybuf *buf = &dc->writeback_keys;
-        bool searched_from_start = false;
-        struct bkey end = MAX_KEY;
-        SET_KEY_INODE(&end, dc->disk.id);
-
-        if (!atomic_read(&dc->disk.detaching) &&
-            !dc->writeback_running)
-                closure_return(cl);
-
-        down_write(&dc->writeback_lock);
-
-        if (!atomic_read(&dc->has_dirty)) {
-                SET_BDEV_STATE(&dc->sb, BDEV_STATE_CLEAN);
-                bch_write_bdev_super(dc, NULL);
-
-                up_write(&dc->writeback_lock);
-                closure_return(cl);
-        }
-
-        if (bkey_cmp(&buf->last_scanned, &end) >= 0) {
-                buf->last_scanned = KEY(dc->disk.id, 0, 0);
-                searched_from_start = true;
-        }
-
-        if (dc->partial_stripes_expensive) {
-                uint64_t i;
-
-                for (i = 0; i < dc->disk.nr_stripes; i++)
-                        if (atomic_read(dc->disk.stripe_sectors_dirty + i) ==
-                            dc->disk.stripe_size)
-                                goto full_stripes;
-
-                goto normal_refill;
-full_stripes:
-                searched_from_start = false;    /* not searching entire btree */
-                bch_refill_keybuf(dc->disk.c, buf, &end,
-                                  dirty_full_stripe_pred);
-        } else {
-normal_refill:
-                bch_refill_keybuf(dc->disk.c, buf, &end, dirty_pred);
-        }
-
-        if (bkey_cmp(&buf->last_scanned, &end) >= 0 && searched_from_start) {
-                /* Searched the entire btree  - delay awhile */
-
-                if (RB_EMPTY_ROOT(&buf->keys)) {
-                        atomic_set(&dc->has_dirty, 0);
-                        cached_dev_put(dc);
-                }
-
-                if (!atomic_read(&dc->disk.detaching))
-                        closure_delay(&dc->writeback, dc->writeback_delay * HZ);
-        }
-
-        up_write(&dc->writeback_lock);
-
-        bch_ratelimit_reset(&dc->writeback_rate);
-
-        /* Punt to workqueue only so we don't recurse and blow the stack */
-        continue_at(cl, read_dirty, dirty_wq);
-}
-
-void bch_writeback_queue(struct cached_dev *dc)
-{
-        if (closure_trylock(&dc->writeback.cl, &dc->disk.cl)) {
-                if (!atomic_read(&dc->disk.detaching))
-                        closure_delay(&dc->writeback, dc->writeback_delay * HZ);
-
-                continue_at(&dc->writeback.cl, refill_dirty, dirty_wq);
-        }
-}
-
-void bch_writeback_add(struct cached_dev *dc)
-{
-        if (!atomic_read(&dc->has_dirty) &&
-            !atomic_xchg(&dc->has_dirty, 1)) {
-                atomic_inc(&dc->count);
-
-                if (BDEV_STATE(&dc->sb) != BDEV_STATE_DIRTY) {
-                        SET_BDEV_STATE(&dc->sb, BDEV_STATE_DIRTY);
-                        /* XXX: should do this synchronously */
-                        bch_write_bdev_super(dc, NULL);
-                }
-
-                bch_writeback_queue(dc);
-
-                if (dc->writeback_percent)
-                        schedule_delayed_work(&dc->writeback_rate_update,
-                                      dc->writeback_rate_update_seconds * HZ);
-        }
-}
-
-void bcache_dev_sectors_dirty_add(struct cache_set *c, unsigned inode,
-                                  uint64_t offset, int nr_sectors)
-{
-        struct bcache_device *d = c->devices[inode];
-        unsigned stripe_offset;
-        uint64_t stripe = offset;
-
-        if (!d)
-                return;
-
-        do_div(stripe, d->stripe_size);
-
-        stripe_offset = offset & (d->stripe_size - 1);
-
-        while (nr_sectors) {
-                int s = min_t(unsigned, abs(nr_sectors),
-                              d->stripe_size - stripe_offset);
-
-                if (nr_sectors < 0)
-                        s = -s;
-
-                atomic_add(s, d->stripe_sectors_dirty + stripe);
-                nr_sectors -= s;
-                stripe_offset = 0;
-                stripe++;
-        }
-}
-
-/* Background writeback - IO loop */
-
 static void dirty_io_destructor(struct closure *cl)
 {
         struct dirty_io *io = container_of(cl, struct dirty_io, cl);
@@ -378,30 +219,33 @@ static void read_dirty_submit(struct closure *cl)
         continue_at(cl, write_dirty, system_wq);
 }
 
-static void read_dirty(struct closure *cl)
+static void read_dirty(struct cached_dev *dc)
 {
-        struct cached_dev *dc = container_of(cl, struct cached_dev,
-                                             writeback.cl);
-        unsigned delay = writeback_delay(dc, 0);
+        unsigned delay = 0;
         struct keybuf_key *w;
         struct dirty_io *io;
+        struct closure cl;
+
+        closure_init_stack(&cl);
 
         /*
          * XXX: if we error, background writeback just spins. Should use some
          * mempools.
          */
 
-        while (1) {
+        while (!kthread_should_stop()) {
+                try_to_freeze();
+
                 w = bch_keybuf_next(&dc->writeback_keys);
                 if (!w)
                         break;
 
                 BUG_ON(ptr_stale(dc->disk.c, &w->key, 0));
 
-                if (delay > 0 &&
-                    (KEY_START(&w->key) != dc->last_read ||
-                     jiffies_to_msecs(delay) > 50))
-                        delay = schedule_timeout_uninterruptible(delay);
+                if (KEY_START(&w->key) != dc->last_read ||
+                    jiffies_to_msecs(delay) > 50)
+                        while (!kthread_should_stop() && delay)
+                                delay = schedule_timeout_interruptible(delay);
 
                 dc->last_read   = KEY_OFFSET(&w->key);
 
@@ -427,7 +271,7 @@ static void read_dirty(struct closure *cl)
                 trace_bcache_writeback(&w->key);
 
                 down(&dc->in_flight);
-                closure_call(&io->cl, read_dirty_submit, NULL, cl);
+                closure_call(&io->cl, read_dirty_submit, NULL, &cl);
 
                 delay = writeback_delay(dc, KEY_SIZE(&w->key));
         }
@@ -443,7 +287,148 @@ err:
          * Wait for outstanding writeback IOs to finish (and keybuf slots to be
          * freed) before refilling again
          */
-        continue_at(cl, refill_dirty, dirty_wq);
+        closure_sync(&cl);
+}
+
+/* Scan for dirty data */
+
+void bcache_dev_sectors_dirty_add(struct cache_set *c, unsigned inode,
+                                  uint64_t offset, int nr_sectors)
+{
+        struct bcache_device *d = c->devices[inode];
+        unsigned stripe_offset;
+        uint64_t stripe = offset;
+
+        if (!d)
+                return;
+
+        do_div(stripe, d->stripe_size);
+
+        stripe_offset = offset & (d->stripe_size - 1);
+
+        while (nr_sectors) {
+                int s = min_t(unsigned, abs(nr_sectors),
+                              d->stripe_size - stripe_offset);
+
+                if (nr_sectors < 0)
+                        s = -s;
+
+                atomic_add(s, d->stripe_sectors_dirty + stripe);
+                nr_sectors -= s;
+                stripe_offset = 0;
+                stripe++;
+        }
+}
+
+static bool dirty_pred(struct keybuf *buf, struct bkey *k)
+{
+        return KEY_DIRTY(k);
+}
+
+static bool dirty_full_stripe_pred(struct keybuf *buf, struct bkey *k)
+{
+        uint64_t stripe = KEY_START(k);
+        unsigned nr_sectors = KEY_SIZE(k);
+        struct cached_dev *dc = container_of(buf, struct cached_dev,
+                                             writeback_keys);
+
+        if (!KEY_DIRTY(k))
+                return false;
+
+        do_div(stripe, dc->disk.stripe_size);
+
+        while (1) {
+                if (atomic_read(dc->disk.stripe_sectors_dirty + stripe) ==
+                    dc->disk.stripe_size)
+                        return true;
+
+                if (nr_sectors <= dc->disk.stripe_size)
+                        return false;
+
+                nr_sectors -= dc->disk.stripe_size;
+                stripe++;
+        }
+}
+
+static bool refill_dirty(struct cached_dev *dc)
+{
+        struct keybuf *buf = &dc->writeback_keys;
+        bool searched_from_start = false;
+        struct bkey end = KEY(dc->disk.id, MAX_KEY_OFFSET, 0);
+
+        if (bkey_cmp(&buf->last_scanned, &end) >= 0) {
+                buf->last_scanned = KEY(dc->disk.id, 0, 0);
+                searched_from_start = true;
+        }
+
+        if (dc->partial_stripes_expensive) {
+                uint64_t i;
+
+                for (i = 0; i < dc->disk.nr_stripes; i++)
+                        if (atomic_read(dc->disk.stripe_sectors_dirty + i) ==
+                            dc->disk.stripe_size)
+                                goto full_stripes;
+
+                goto normal_refill;
+full_stripes:
+                searched_from_start = false;    /* not searching entire btree */
+                bch_refill_keybuf(dc->disk.c, buf, &end,
+                                  dirty_full_stripe_pred);
+        } else {
+normal_refill:
+                bch_refill_keybuf(dc->disk.c, buf, &end, dirty_pred);
+        }
+
+        return bkey_cmp(&buf->last_scanned, &end) >= 0 && searched_from_start;
+}
+
+static int bch_writeback_thread(void *arg)
+{
+        struct cached_dev *dc = arg;
+        bool searched_full_index;
+
+        while (!kthread_should_stop()) {
+                down_write(&dc->writeback_lock);
+                if (!atomic_read(&dc->has_dirty) ||
+                    (!atomic_read(&dc->disk.detaching) &&
+                     !dc->writeback_running)) {
+                        up_write(&dc->writeback_lock);
+                        set_current_state(TASK_INTERRUPTIBLE);
+
+                        if (kthread_should_stop())
+                                return 0;
+
+                        try_to_freeze();
+                        schedule();
+                        continue;
+                }
+
+                searched_full_index = refill_dirty(dc);
+
+                if (searched_full_index &&
+                    RB_EMPTY_ROOT(&dc->writeback_keys.keys)) {
+                        atomic_set(&dc->has_dirty, 0);
+                        cached_dev_put(dc);
+                        SET_BDEV_STATE(&dc->sb, BDEV_STATE_CLEAN);
+                        bch_write_bdev_super(dc, NULL);
+                }
+
+                up_write(&dc->writeback_lock);
+
+                bch_ratelimit_reset(&dc->writeback_rate);
+                read_dirty(dc);
+
+                if (searched_full_index) {
+                        unsigned delay = dc->writeback_delay * HZ;
+
+                        while (delay &&
+                               !kthread_should_stop() &&
+                               !atomic_read(&dc->disk.detaching))
+                                delay = schedule_timeout_interruptible(delay);
+                }
+        }
+
+        return 0;
 }
 
 /* Init */
@@ -483,12 +468,10 @@ void bch_sectors_dirty_init(struct cached_dev *dc)
         btree_root(sectors_dirty_init, dc->disk.c, &op, dc);
 }
 
-void bch_cached_dev_writeback_init(struct cached_dev *dc)
+int bch_cached_dev_writeback_init(struct cached_dev *dc)
 {
         sema_init(&dc->in_flight, 64);
-        closure_init_unlocked(&dc->writeback);
         init_rwsem(&dc->writeback_lock);
-
         bch_keybuf_init(&dc->writeback_keys);
 
         dc->writeback_metadata          = true;
@@ -502,22 +485,16 @@ void bch_cached_dev_writeback_init(struct cached_dev *dc)
         dc->writeback_rate_p_term_inverse = 64;
         dc->writeback_rate_d_smooth     = 8;
 
+        dc->writeback_thread = kthread_create(bch_writeback_thread, dc,
+                                              "bcache_writeback");
+        if (IS_ERR(dc->writeback_thread))
+                return PTR_ERR(dc->writeback_thread);
+
+        set_task_state(dc->writeback_thread, TASK_INTERRUPTIBLE);
+
         INIT_DELAYED_WORK(&dc->writeback_rate_update, update_writeback_rate);
         schedule_delayed_work(&dc->writeback_rate_update,
                               dc->writeback_rate_update_seconds * HZ);
-}
-
-void bch_writeback_exit(void)
-{
-        if (dirty_wq)
-                destroy_workqueue(dirty_wq);
-}
-
-int __init bch_writeback_init(void)
-{
-        dirty_wq = create_workqueue("bcache_writeback");
-        if (!dirty_wq)
-                return -ENOMEM;
 
         return 0;
 }
diff --git a/drivers/md/bcache/writeback.h b/drivers/md/bcache/writeback.h
index 34961888b5a9..60516bfa6052 100644
--- a/drivers/md/bcache/writeback.h
+++ b/drivers/md/bcache/writeback.h
@@ -56,11 +56,30 @@ static inline bool should_writeback(struct cached_dev *dc, struct bio *bio,
                 in_use <= CUTOFF_WRITEBACK;
 }
 
+static inline void bch_writeback_queue(struct cached_dev *dc)
+{
+        wake_up_process(dc->writeback_thread);
+}
+
+static inline void bch_writeback_add(struct cached_dev *dc)
+{
+        if (!atomic_read(&dc->has_dirty) &&
+            !atomic_xchg(&dc->has_dirty, 1)) {
+                atomic_inc(&dc->count);
+
+                if (BDEV_STATE(&dc->sb) != BDEV_STATE_DIRTY) {
+                        SET_BDEV_STATE(&dc->sb, BDEV_STATE_DIRTY);
+                        /* XXX: should do this synchronously */
+                        bch_write_bdev_super(dc, NULL);
+                }
+
+                bch_writeback_queue(dc);
+        }
+}
+
 void bcache_dev_sectors_dirty_add(struct cache_set *, unsigned, uint64_t, int);
-void bch_writeback_queue(struct cached_dev *);
-void bch_writeback_add(struct cached_dev *);
 
 void bch_sectors_dirty_init(struct cached_dev *dc);
-void bch_cached_dev_writeback_init(struct cached_dev *);
+int bch_cached_dev_writeback_init(struct cached_dev *);
 
 #endif