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Commit 5e6926da authored by Kent Overstreet's avatar Kent Overstreet
Browse files

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: default avatarKent Overstreet <kmo@daterainc.com>
parent 72a44517

drivers/md/bcache/bcache.h

+6 −4
Original line number Diff line number Diff line
@@ -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);

drivers/md/bcache/super.c

+1 −2
Original line number Diff line number Diff line
@@ -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;

drivers/md/bcache/writeback.c

+174 −197
Original line number Diff line number Diff line
@@ -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 @@ static void __update_writeback_rate(struct cached_dev *dc) 
	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 @@ static void read_dirty(struct closure *cl) 
	 * 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;

}

drivers/md/bcache/writeback.h

+22 −3
Original line number Diff line number Diff line
@@ -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