path: root/block.patch

To: LKML <linux-kernel@vger.kernel.org>, Jens Axboe <axboe@fb.com>
From: =?UTF-8?Q?Holger_Hoffst=c3=a4tte?= <holger.hoffstaette@googlemail.com>
Subject: [PATCH] loop: properly observe rotational flag of underlying device
Organization: Applied Asynchrony, Inc.
Date: Wed, 11 Nov 2015 16:21:51 +0100

The loop driver always declares the rotational flag of its device as
rotational, even when the device of the mapped file is nonrotational,
as is the case with SSDs or on tmpfs. This can confuse filesystem tools
which are SSD-aware; in my case I frequently forget to tell mkfs.btrfs
that my loop device on tmpfs is nonrotational, and that I really don't
need any automatic metadata redundancy.

The attached patch fixes this by introspecting the rotational flag of the
mapped file's underlying block device, if it exists. If the mapped file's
filesystem has no associated block device - as is the case on e.g. tmpfs -
we assume nonrotational storage. If there is a better way to identify such
non-devices I'd love to hear them.

Signed-off-by: Holger Hoffstätte <holger.hoffstaette@googlemail.com>
---
 drivers/block/loop.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 423f4ca..2984aca 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -843,6 +843,24 @@ static void loop_config_discard(struct loop_device *lo)
 	queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, q);
 }
 
+static void loop_update_rotational(struct loop_device *lo)
+{
+	struct file *file = lo->lo_backing_file;
+	struct inode *file_inode = file->f_mapping->host;
+	struct block_device *file_bdev = file_inode->i_sb->s_bdev;
+	struct request_queue *q = lo->lo_queue;
+	bool nonrot = true;
+
+	/* not all filesystems (e.g. tmpfs) have a sb->s_bdev */
+	if (file_bdev)
+		nonrot = blk_queue_nonrot(bdev_get_queue(file_bdev));
+
+	if (nonrot)
+		queue_flag_set_unlocked(QUEUE_FLAG_NONROT, q);
+	else
+		queue_flag_clear_unlocked(QUEUE_FLAG_NONROT, q);
+}
+
 static void loop_unprepare_queue(struct loop_device *lo)
 {
 	flush_kthread_worker(&lo->worker);
@@ -939,6 +957,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
 	if (!(lo_flags & LO_FLAGS_READ_ONLY) && file->f_op->fsync)
 		blk_queue_flush(lo->lo_queue, REQ_FLUSH);
 
+	loop_update_rotational(lo);
 	loop_update_dio(lo);
 	set_capacity(lo->lo_disk, size);
 	bd_set_size(bdev, size << 9);
-- 
2.6.3
From 273d4cb9fc3d75b6b7f147d1a064f75a5412a76c Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@fb.com>
Date: Wed, 27 Jul 2016 15:30:35 -0600
Subject: block: add WRITE_BG

This adds a new request flag, REQ_BG, that callers can use to tell
the block layer that this is background (non-urgent) IO.

Signed-off-by: Jens Axboe <axboe@fb.com>
---
 include/linux/blk_types.h | 4 +++-
 include/linux/fs.h        | 3 +++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 436f43f..be4409b 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -155,6 +155,7 @@ enum rq_flag_bits {
 	__REQ_INTEGRITY,	/* I/O includes block integrity payload */
 	__REQ_FUA,		/* forced unit access */
 	__REQ_PREFLUSH,		/* request for cache flush */
+	__REQ_BG,		/* background activity */
 
 	/* bio only flags */
 	__REQ_RAHEAD,		/* read ahead, can fail anytime */
@@ -198,7 +199,7 @@ enum rq_flag_bits {
 	(REQ_FAILFAST_DEV | REQ_FAILFAST_TRANSPORT | REQ_FAILFAST_DRIVER)
 #define REQ_COMMON_MASK \
 	(REQ_FAILFAST_MASK | REQ_SYNC | REQ_META | REQ_PRIO | REQ_NOIDLE | \
-	 REQ_PREFLUSH | REQ_FUA | REQ_INTEGRITY | REQ_NOMERGE)
+	 REQ_PREFLUSH | REQ_FUA | REQ_INTEGRITY | REQ_NOMERGE | REQ_BG)
 #define REQ_CLONE_MASK		REQ_COMMON_MASK
 
 /* This mask is used for both bio and request merge checking */
@@ -223,6 +224,7 @@ enum rq_flag_bits {
 #define REQ_COPY_USER		(1ULL << __REQ_COPY_USER)
 #define REQ_PREFLUSH		(1ULL << __REQ_PREFLUSH)
 #define REQ_FLUSH_SEQ		(1ULL << __REQ_FLUSH_SEQ)
+#define REQ_BG			(1ULL << __REQ_BG)
 #define REQ_IO_STAT		(1ULL << __REQ_IO_STAT)
 #define REQ_MIXED_MERGE		(1ULL << __REQ_MIXED_MERGE)
 #define REQ_PM			(1ULL << __REQ_PM)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 901e25d..7c7951f 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -189,6 +189,8 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
  * WRITE_FLUSH_FUA	Combination of WRITE_FLUSH and FUA. The IO is preceded
  *			by a cache flush and data is guaranteed to be on
  *			non-volatile media on completion.
+ * WRITE_BG		Background write. This is for background activity like
+ *			the periodic flush and background threshold writeback
  *
  */
 #define RW_MASK			REQ_OP_WRITE
@@ -202,6 +204,7 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
 #define WRITE_FLUSH		(REQ_SYNC | REQ_NOIDLE | REQ_PREFLUSH)
 #define WRITE_FUA		(REQ_SYNC | REQ_NOIDLE | REQ_FUA)
 #define WRITE_FLUSH_FUA		(REQ_SYNC | REQ_NOIDLE | REQ_PREFLUSH | REQ_FUA)
+#define WRITE_BG		(REQ_NOIDLE | REQ_BG)
 
 /*
  * Attribute flags.  These should be or-ed together to figure out what
-- 
cgit v0.11.2

From 33a170c4f076584bc05feb19efa7beb0ee099318 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@fb.com>
Date: Wed, 27 Jul 2016 15:24:08 -0600
Subject: writeback: add wbc_to_write_flags()

Add wbc_to_write_flags(), which returns the write modifier flags to use,
based on a struct writeback_control. No functional changes in this
patch, but it prepares us for factoring other wbc fields for write type.

Signed-off-by: Jens Axboe <axboe@fb.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 fs/buffer.c               | 2 +-
 fs/f2fs/data.c            | 2 +-
 fs/f2fs/node.c            | 2 +-
 fs/gfs2/meta_io.c         | 3 +--
 fs/mpage.c                | 2 +-
 fs/xfs/xfs_aops.c         | 7 +++----
 include/linux/writeback.h | 8 ++++++++
 7 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 9c8eb9b..6a5f1a0 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1698,7 +1698,7 @@ int __block_write_full_page(struct inode *inode, struct page *page,
 	struct buffer_head *bh, *head;
 	unsigned int blocksize, bbits;
 	int nr_underway = 0;
-	int write_flags = (wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC : 0);
+	int write_flags = wbc_to_write_flags(wbc);
 
 	head = create_page_buffers(page, inode,
 					(1 << BH_Dirty)|(1 << BH_Uptodate));
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index ccb401e..cb0528b 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -1240,7 +1240,7 @@ static int f2fs_write_data_page(struct page *page,
 		.sbi = sbi,
 		.type = DATA,
 		.op = REQ_OP_WRITE,
-		.op_flags = (wbc->sync_mode == WB_SYNC_ALL) ? WRITE_SYNC : 0,
+		.op_flags = wbc_to_write_flags(wbc),
 		.page = page,
 		.encrypted_page = NULL,
 	};
diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index f75d197..c1713da 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -1561,7 +1561,7 @@ static int f2fs_write_node_page(struct page *page,
 		.sbi = sbi,
 		.type = NODE,
 		.op = REQ_OP_WRITE,
-		.op_flags = (wbc->sync_mode == WB_SYNC_ALL) ? WRITE_SYNC : 0,
+		.op_flags = wbc_to_write_flags(wbc),
 		.page = page,
 		.encrypted_page = NULL,
 	};
diff --git a/fs/gfs2/meta_io.c b/fs/gfs2/meta_io.c
index 950b8be..7991c62 100644
--- a/fs/gfs2/meta_io.c
+++ b/fs/gfs2/meta_io.c
@@ -37,8 +37,7 @@ static int gfs2_aspace_writepage(struct page *page, struct writeback_control *wb
 {
 	struct buffer_head *bh, *head;
 	int nr_underway = 0;
-	int write_flags = REQ_META | REQ_PRIO |
-		(wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC : 0);
+	int write_flags = REQ_META | REQ_PRIO | wbc_to_write_flags(wbc);
 
 	BUG_ON(!PageLocked(page));
 	BUG_ON(!page_has_buffers(page));
diff --git a/fs/mpage.c b/fs/mpage.c
index d2413af..d6f1afe 100644
--- a/fs/mpage.c
+++ b/fs/mpage.c
@@ -489,7 +489,7 @@ static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
 	struct buffer_head map_bh;
 	loff_t i_size = i_size_read(inode);
 	int ret = 0;
-	int op_flags = (wbc->sync_mode == WB_SYNC_ALL ?  WRITE_SYNC : 0);
+	int op_flags = wbc_to_write_flags(wbc);
 
 	if (page_has_buffers(page)) {
 		struct buffer_head *head = page_buffers(page);
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 7575cfc..a68645a 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -447,8 +447,8 @@ xfs_submit_ioend(
 
 	ioend->io_bio->bi_private = ioend;
 	ioend->io_bio->bi_end_io = xfs_end_bio;
-	bio_set_op_attrs(ioend->io_bio, REQ_OP_WRITE,
-			 (wbc->sync_mode == WB_SYNC_ALL) ? WRITE_SYNC : 0);
+	bio_set_op_attrs(ioend->io_bio, REQ_OP_WRITE, wbc_to_write_flags(wbc));
+
 	/*
 	 * If we are failing the IO now, just mark the ioend with an
 	 * error and finish it. This will run IO completion immediately
@@ -519,8 +519,7 @@ xfs_chain_bio(
 
 	bio_chain(ioend->io_bio, new);
 	bio_get(ioend->io_bio);		/* for xfs_destroy_ioend */
-	bio_set_op_attrs(ioend->io_bio, REQ_OP_WRITE,
-			  (wbc->sync_mode == WB_SYNC_ALL) ? WRITE_SYNC : 0);
+	bio_set_op_attrs(ioend->io_bio, REQ_OP_WRITE, wbc_to_write_flags(wbc));
 	submit_bio(ioend->io_bio);
 	ioend->io_bio = new;
 }
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index fc1e16c..608afd3 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -100,6 +100,14 @@ struct writeback_control {
 #endif
 };
 
+static inline int wbc_to_write_flags(struct writeback_control *wbc)
+{
+	if (wbc->sync_mode == WB_SYNC_ALL)
+		return WRITE_SYNC;
+
+	return 0;
+}
+
 /*
  * A wb_domain represents a domain that wb's (bdi_writeback's) belong to
  * and are measured against each other in.  There always is one global
-- 
cgit v0.11.2

From d6cf7bfd4d627114ba3e2cce96fa9468042a6fba Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@fb.com>
Date: Thu, 14 Apr 2016 09:53:24 -0600
Subject: writeback: use WRITE_BG for kupdate and background writeback

If we're doing background type writes, then use the appropriate
write command for that.

Signed-off-by: Jens Axboe <axboe@fb.com>
---
 include/linux/writeback.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 608afd3..e53abf2 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -104,6 +104,8 @@ static inline int wbc_to_write_flags(struct writeback_control *wbc)
 {
 	if (wbc->sync_mode == WB_SYNC_ALL)
 		return WRITE_SYNC;
+	else if (wbc->for_kupdate || wbc->for_background)
+		return WRITE_BG;
 
 	return 0;
 }
-- 
cgit v0.11.2

From cd38cff40da34de0bf78f8305c89bdfafc606e7f Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@fb.com>
Date: Thu, 1 Sep 2016 10:20:33 -0600
Subject: writeback: track if we're sleeping on progress in
 balance_dirty_pages()

Note in the bdi_writeback structure whenever a task ends up sleeping
waiting for progress. We can use that information in the lower layers
to increase the priority of writes.

Signed-off-by: Jens Axboe <axboe@fb.com>
---
 include/linux/backing-dev-defs.h | 2 ++
 mm/backing-dev.c                 | 1 +
 mm/page-writeback.c              | 1 +
 3 files changed, 4 insertions(+)

diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index c357f27..dc5f76d 100644
--- a/include/linux/backing-dev-defs.h
+++ b/include/linux/backing-dev-defs.h
@@ -116,6 +116,8 @@ struct bdi_writeback {
 	struct list_head work_list;
 	struct delayed_work dwork;	/* work item used for writeback */
 
+	unsigned long dirty_sleep;	/* last wait */
+
 	struct list_head bdi_node;	/* anchored at bdi->wb_list */
 
 #ifdef CONFIG_CGROUP_WRITEBACK
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 8fde443..3bfed5ab 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -310,6 +310,7 @@ static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi,
 	spin_lock_init(&wb->work_lock);
 	INIT_LIST_HEAD(&wb->work_list);
 	INIT_DELAYED_WORK(&wb->dwork, wb_workfn);
+	wb->dirty_sleep = jiffies;
 
 	wb->congested = wb_congested_get_create(bdi, blkcg_id, gfp);
 	if (!wb->congested)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index f4cd7d8..98bc3fc 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1778,6 +1778,7 @@ pause:
 					  pause,
 					  start_time);
 		__set_current_state(TASK_KILLABLE);
+		wb->dirty_sleep = now;
 		io_schedule_timeout(pause);
 
 		current->dirty_paused_when = now + pause;
-- 
cgit v0.11.2

From a98f5ab3840c2e6008c478aafe5df055404acdd1 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@fb.com>
Date: Wed, 30 Mar 2016 10:21:08 -0600
Subject: block: add code to track actual device queue depth

For blk-mq, ->nr_requests does track queue depth, at least at init
time. But for the older queue paths, it's simply a soft setting.
On top of that, it's generally larger than the hardware setting
on purpose, to allow backup of requests for merging.

Fill a hole in struct request with a 'queue_depth' member, that
drivers can call to more closely inform the block layer of the
real queue depth.

Signed-off-by: Jens Axboe <axboe@fb.com>
---
 block/blk-settings.c   | 12 ++++++++++++
 drivers/scsi/scsi.c    |  3 +++
 include/linux/blkdev.h | 11 +++++++++++
 3 files changed, 26 insertions(+)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index f679ae1..f7e122e 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -832,6 +832,18 @@ void blk_queue_flush_queueable(struct request_queue *q, bool queueable)
 EXPORT_SYMBOL_GPL(blk_queue_flush_queueable);
 
 /**
+ * blk_set_queue_depth - tell the block layer about the device queue depth
+ * @q:		the request queue for the device
+ * @depth:		queue depth
+ *
+ */
+void blk_set_queue_depth(struct request_queue *q, unsigned int depth)
+{
+	q->queue_depth = depth;
+}
+EXPORT_SYMBOL(blk_set_queue_depth);
+
+/**
  * blk_queue_write_cache - configure queue's write cache
  * @q:		the request queue for the device
  * @wc:		write back cache on or off
diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index 1f36aca..f3de98a 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -621,6 +621,9 @@ int scsi_change_queue_depth(struct scsi_device *sdev, int depth)
 		wmb();
 	}
 
+	if (sdev->request_queue)
+		blk_set_queue_depth(sdev->request_queue, depth);
+
 	return sdev->queue_depth;
 }
 EXPORT_SYMBOL(scsi_change_queue_depth);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index e79055c..1d12aa6 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -327,6 +327,8 @@ struct request_queue {
 	struct blk_mq_ctx __percpu	*queue_ctx;
 	unsigned int		nr_queues;
 
+	unsigned int		queue_depth;
+
 	/* hw dispatch queues */
 	struct blk_mq_hw_ctx	**queue_hw_ctx;
 	unsigned int		nr_hw_queues;
@@ -683,6 +685,14 @@ static inline bool blk_write_same_mergeable(struct bio *a, struct bio *b)
 	return false;
 }
 
+static inline unsigned int blk_queue_depth(struct request_queue *q)
+{
+	if (q->queue_depth)
+		return q->queue_depth;
+
+	return q->nr_requests;
+}
+
 /*
  * q->prep_rq_fn return values
  */
@@ -999,6 +1009,7 @@ extern void blk_limits_io_min(struct queue_limits *limits, unsigned int min);
 extern void blk_queue_io_min(struct request_queue *q, unsigned int min);
 extern void blk_limits_io_opt(struct queue_limits *limits, unsigned int opt);
 extern void blk_queue_io_opt(struct request_queue *q, unsigned int opt);
+extern void blk_set_queue_depth(struct request_queue *q, unsigned int depth);
 extern void blk_set_default_limits(struct queue_limits *lim);
 extern void blk_set_stacking_limits(struct queue_limits *lim);
 extern int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
-- 
cgit v0.11.2

From a13cc5885ddd5582129869c1837821d6af6d48bb Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@fb.com>
Date: Thu, 1 Sep 2016 10:22:41 -0600
Subject: block: add scalable completion tracking of requests

For legacy block, we simply track them in the request queue. For
blk-mq, we track them on a per-sw queue basis, which we can then
sum up through the hardware queues and finally to a per device
state.

The stats are tracked in, roughly, 0.1s interval windows.

Add sysfs files to display the stats.

Signed-off-by: Jens Axboe <axboe@fb.com>
---
 block/Makefile            |   2 +-
 block/blk-core.c          |   4 +
 block/blk-mq-sysfs.c      |  47 ++++++++++
 block/blk-mq.c            |  14 +++
 block/blk-mq.h            |   3 +
 block/blk-stat.c          | 220 ++++++++++++++++++++++++++++++++++++++++++++++
 block/blk-stat.h          |  18 ++++
 block/blk-sysfs.c         |  26 ++++++
 include/linux/blk_types.h |  12 +++
 include/linux/blkdev.h    |   4 +
 10 files changed, 349 insertions(+), 1 deletion(-)
 create mode 100644 block/blk-stat.c
 create mode 100644 block/blk-stat.h

diff --git a/block/Makefile b/block/Makefile
index 9eda232..3446e04 100644
--- a/block/Makefile
+++ b/block/Makefile
@@ -5,7 +5,7 @@
 obj-$(CONFIG_BLOCK) := bio.o elevator.o blk-core.o blk-tag.o blk-sysfs.o \
 			blk-flush.o blk-settings.o blk-ioc.o blk-map.o \
 			blk-exec.o blk-merge.o blk-softirq.o blk-timeout.o \
-			blk-lib.o blk-mq.o blk-mq-tag.o \
+			blk-lib.o blk-mq.o blk-mq-tag.o blk-stat.o \
 			blk-mq-sysfs.o blk-mq-cpu.o blk-mq-cpumap.o ioctl.o \
 			genhd.o scsi_ioctl.o partition-generic.o ioprio.o \
 			badblocks.o partitions/
diff --git a/block/blk-core.c b/block/blk-core.c
index 36c7ac3..4075cbe 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2475,6 +2475,8 @@ void blk_start_request(struct request *req)
 {
 	blk_dequeue_request(req);
 
+	req->issue_time = ktime_to_ns(ktime_get());
+
 	/*
 	 * We are now handing the request to the hardware, initialize
 	 * resid_len to full count and add the timeout handler.
@@ -2542,6 +2544,8 @@ bool blk_update_request(struct request *req, int error, unsigned int nr_bytes)
 
 	trace_block_rq_complete(req->q, req, nr_bytes);
 
+	blk_stat_add(&req->q->rq_stats[rq_data_dir(req)], req);
+
 	if (!req->bio)
 		return false;
 
diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
index fe822aa..b66bbf1 100644
--- a/block/blk-mq-sysfs.c
+++ b/block/blk-mq-sysfs.c
@@ -247,6 +247,47 @@ static ssize_t blk_mq_hw_sysfs_cpus_show(struct blk_mq_hw_ctx *hctx, char *page)
 	return ret;
 }
 
+static void blk_mq_stat_clear(struct blk_mq_hw_ctx *hctx)
+{
+	struct blk_mq_ctx *ctx;
+	unsigned int i;
+
+	hctx_for_each_ctx(hctx, ctx, i) {
+		blk_stat_init(&ctx->stat[0]);
+		blk_stat_init(&ctx->stat[1]);
+	}
+}
+
+static ssize_t blk_mq_hw_sysfs_stat_store(struct blk_mq_hw_ctx *hctx,
+					  const char *page, size_t count)
+{
+	blk_mq_stat_clear(hctx);
+	return count;
+}
+
+static ssize_t print_stat(char *page, struct blk_rq_stat *stat, const char *pre)
+{
+	return sprintf(page, "%s samples=%llu, mean=%lld, min=%lld, max=%lld\n",
+			pre, (long long) stat->nr_samples,
+			(long long) stat->mean, (long long) stat->min,
+			(long long) stat->max);
+}
+
+static ssize_t blk_mq_hw_sysfs_stat_show(struct blk_mq_hw_ctx *hctx, char *page)
+{
+	struct blk_rq_stat stat[2];
+	ssize_t ret;
+
+	blk_stat_init(&stat[0]);
+	blk_stat_init(&stat[1]);
+
+	blk_hctx_stat_get(hctx, stat);
+
+	ret = print_stat(page, &stat[0], "read :");
+	ret += print_stat(page + ret, &stat[1], "write:");
+	return ret;
+}
+
 static struct blk_mq_ctx_sysfs_entry blk_mq_sysfs_dispatched = {
 	.attr = {.name = "dispatched", .mode = S_IRUGO },
 	.show = blk_mq_sysfs_dispatched_show,
@@ -304,6 +345,11 @@ static struct blk_mq_hw_ctx_sysfs_entry blk_mq_hw_sysfs_poll = {
 	.attr = {.name = "io_poll", .mode = S_IRUGO },
 	.show = blk_mq_hw_sysfs_poll_show,
 };
+static struct blk_mq_hw_ctx_sysfs_entry blk_mq_hw_sysfs_stat = {
+	.attr = {.name = "stats", .mode = S_IRUGO | S_IWUSR },
+	.show = blk_mq_hw_sysfs_stat_show,
+	.store = blk_mq_hw_sysfs_stat_store,
+};
 
 static struct attribute *default_hw_ctx_attrs[] = {
 	&blk_mq_hw_sysfs_queued.attr,
@@ -314,6 +360,7 @@ static struct attribute *default_hw_ctx_attrs[] = {
 	&blk_mq_hw_sysfs_cpus.attr,
 	&blk_mq_hw_sysfs_active.attr,
 	&blk_mq_hw_sysfs_poll.attr,
+	&blk_mq_hw_sysfs_stat.attr,
 	NULL,
 };
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 13f5a6c..712f141 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -29,6 +29,7 @@
 #include "blk.h"
 #include "blk-mq.h"
 #include "blk-mq-tag.h"
+#include "blk-stat.h"
 
 static DEFINE_MUTEX(all_q_mutex);
 static LIST_HEAD(all_q_list);
@@ -400,10 +401,19 @@ static void blk_mq_ipi_complete_request(struct request *rq)
 	put_cpu();
 }
 
+static void blk_mq_stat_add(struct request *rq)
+{
+	struct blk_rq_stat *stat = &rq->mq_ctx->stat[rq_data_dir(rq)];
+
+	blk_stat_add(stat, rq);
+}
+
 static void __blk_mq_complete_request(struct request *rq)
 {
 	struct request_queue *q = rq->q;
 
+	blk_mq_stat_add(rq);
+
 	if (!q->softirq_done_fn)
 		blk_mq_end_request(rq, rq->errors);
 	else
@@ -447,6 +457,8 @@ void blk_mq_start_request(struct request *rq)
 	if (unlikely(blk_bidi_rq(rq)))
 		rq->next_rq->resid_len = blk_rq_bytes(rq->next_rq);
 
+	rq->issue_time = ktime_to_ns(ktime_get());
+
 	blk_add_timer(rq);
 
 	/*
@@ -1795,6 +1807,8 @@ static void blk_mq_init_cpu_queues(struct request_queue *q,
 		spin_lock_init(&__ctx->lock);
 		INIT_LIST_HEAD(&__ctx->rq_list);
 		__ctx->queue = q;
+		blk_stat_init(&__ctx->stat[0]);
+		blk_stat_init(&__ctx->stat[1]);
 
 		/* If the cpu isn't online, the cpu is mapped to first hctx */
 		if (!cpu_online(i))
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 9087b11..e107f70 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -1,6 +1,8 @@
 #ifndef INT_BLK_MQ_H
 #define INT_BLK_MQ_H
 
+#include "blk-stat.h"
+
 struct blk_mq_tag_set;
 
 struct blk_mq_ctx {
@@ -20,6 +22,7 @@ struct blk_mq_ctx {
 
 	/* incremented at completion time */
 	unsigned long		____cacheline_aligned_in_smp rq_completed[2];
+	struct blk_rq_stat	stat[2];
 
 	struct request_queue	*queue;
 	struct kobject		kobj;
diff --git a/block/blk-stat.c b/block/blk-stat.c
new file mode 100644
index 0000000..3965e8a
--- /dev/null
+++ b/block/blk-stat.c
@@ -0,0 +1,220 @@
+/*
+ * Block stat tracking code
+ *
+ * Copyright (C) 2016 Jens Axboe
+ */
+#include <linux/kernel.h>
+#include <linux/blk-mq.h>
+
+#include "blk-stat.h"
+#include "blk-mq.h"
+
+static void blk_stat_flush_batch(struct blk_rq_stat *stat)
+{
+	if (!stat->nr_batch)
+		return;
+	if (!stat->nr_samples)
+		stat->mean = div64_s64(stat->batch, stat->nr_batch);
+	else {
+		stat->mean = div64_s64((stat->mean * stat->nr_samples) +
+					stat->batch,
+					stat->nr_samples + stat->nr_batch);
+	}
+
+	stat->nr_samples += stat->nr_batch;
+	stat->nr_batch = stat->batch = 0;
+}
+
+void blk_stat_sum(struct blk_rq_stat *dst, struct blk_rq_stat *src)
+{
+	if (!src->nr_samples)
+		return;
+
+	blk_stat_flush_batch(src);
+
+	dst->min = min(dst->min, src->min);
+	dst->max = max(dst->max, src->max);
+
+	if (!dst->nr_samples)
+		dst->mean = src->mean;
+	else {
+		dst->mean = div64_s64((src->mean * src->nr_samples) +
+					(dst->mean * dst->nr_samples),
+					dst->nr_samples + src->nr_samples);
+	}
+	dst->nr_samples += src->nr_samples;
+}
+
+static void blk_mq_stat_get(struct request_queue *q, struct blk_rq_stat *dst)
+{
+	struct blk_mq_hw_ctx *hctx;
+	struct blk_mq_ctx *ctx;
+	uint64_t latest = 0;
+	int i, j, nr;
+
+	blk_stat_init(&dst[0]);
+	blk_stat_init(&dst[1]);
+
+	nr = 0;
+	do {
+		uint64_t newest = 0;
+
+		queue_for_each_hw_ctx(q, hctx, i) {
+			hctx_for_each_ctx(hctx, ctx, j) {
+				if (!ctx->stat[0].nr_samples &&
+				    !ctx->stat[1].nr_samples)
+					continue;
+				if (ctx->stat[0].time > newest)
+					newest = ctx->stat[0].time;
+				if (ctx->stat[1].time > newest)
+					newest = ctx->stat[1].time;
+			}
+		}
+
+		/*
+		 * No samples
+		 */
+		if (!newest)
+			break;
+
+		if (newest > latest)
+			latest = newest;
+
+		queue_for_each_hw_ctx(q, hctx, i) {
+			hctx_for_each_ctx(hctx, ctx, j) {
+				if (ctx->stat[0].time == newest) {
+					blk_stat_sum(&dst[0], &ctx->stat[0]);
+					nr++;
+				}
+				if (ctx->stat[1].time == newest) {
+					blk_stat_sum(&dst[1], &ctx->stat[1]);
+					nr++;
+				}
+			}
+		}
+		/*
+		 * If we race on finding an entry, just loop back again.
+		 * Should be very rare.
+		 */
+	} while (!nr);
+
+	dst[0].time = dst[1].time = latest;
+}
+
+void blk_queue_stat_get(struct request_queue *q, struct blk_rq_stat *dst)
+{
+	if (q->mq_ops)
+		blk_mq_stat_get(q, dst);
+	else {
+		memcpy(&dst[0], &q->rq_stats[0], sizeof(struct blk_rq_stat));
+		memcpy(&dst[1], &q->rq_stats[1], sizeof(struct blk_rq_stat));
+	}
+}
+
+void blk_hctx_stat_get(struct blk_mq_hw_ctx *hctx, struct blk_rq_stat *dst)
+{
+	struct blk_mq_ctx *ctx;
+	unsigned int i, nr;
+
+	nr = 0;
+	do {
+		uint64_t newest = 0;
+
+		hctx_for_each_ctx(hctx, ctx, i) {
+			if (!ctx->stat[0].nr_samples &&
+			    !ctx->stat[1].nr_samples)
+				continue;
+
+			if (ctx->stat[0].time > newest)
+				newest = ctx->stat[0].time;
+			if (ctx->stat[1].time > newest)
+				newest = ctx->stat[1].time;
+		}
+
+		if (!newest)
+			break;
+
+		hctx_for_each_ctx(hctx, ctx, i) {
+			if (ctx->stat[0].time == newest) {
+				blk_stat_sum(&dst[0], &ctx->stat[0]);
+				nr++;
+			}
+			if (ctx->stat[1].time == newest) {
+				blk_stat_sum(&dst[1], &ctx->stat[1]);
+				nr++;
+			}
+		}
+		/*
+		 * If we race on finding an entry, just loop back again.
+		 * Should be very rare, as the window is only updated
+		 * occasionally
+		 */
+	} while (!nr);
+}
+
+static void __blk_stat_init(struct blk_rq_stat *stat, s64 time_now)
+{
+	stat->min = -1ULL;
+	stat->max = stat->nr_samples = stat->mean = 0;
+	stat->batch = stat->nr_batch = 0;
+	stat->time = time_now & BLK_STAT_MASK;
+}
+
+void blk_stat_init(struct blk_rq_stat *stat)
+{
+	__blk_stat_init(stat, ktime_to_ns(ktime_get()));
+}
+
+static bool __blk_stat_is_current(struct blk_rq_stat *stat, s64 now)
+{
+	return (now & BLK_STAT_MASK) == (stat->time & BLK_STAT_MASK);
+}
+
+bool blk_stat_is_current(struct blk_rq_stat *stat)
+{
+	return __blk_stat_is_current(stat, ktime_to_ns(ktime_get()));
+}
+
+void blk_stat_add(struct blk_rq_stat *stat, struct request *rq)
+{
+	s64 now, value;
+
+	now = ktime_to_ns(ktime_get());
+	if (now < rq->issue_time)
+		return;
+
+	if (!__blk_stat_is_current(stat, now))
+		__blk_stat_init(stat, now);
+
+	value = now - rq->issue_time;
+	if (value > stat->max)
+		stat->max = value;
+	if (value < stat->min)
+		stat->min = value;
+
+	if (stat->batch + value < stat->batch ||
+	    stat->nr_batch + 1 == BLK_RQ_STAT_BATCH)
+		blk_stat_flush_batch(stat);
+
+	stat->batch += value;
+	stat->nr_batch++;
+}
+
+void blk_stat_clear(struct request_queue *q)
+{
+	if (q->mq_ops) {
+		struct blk_mq_hw_ctx *hctx;
+		struct blk_mq_ctx *ctx;
+		int i, j;
+
+		queue_for_each_hw_ctx(q, hctx, i) {
+			hctx_for_each_ctx(hctx, ctx, j) {
+				blk_stat_init(&ctx->stat[0]);
+				blk_stat_init(&ctx->stat[1]);
+			}
+		}
+	} else {
+		blk_stat_init(&q->rq_stats[0]);
+		blk_stat_init(&q->rq_stats[1]);
+	}
+}
diff --git a/block/blk-stat.h b/block/blk-stat.h
new file mode 100644
index 0000000..376a6cc
--- /dev/null
+++ b/block/blk-stat.h
@@ -0,0 +1,18 @@
+#ifndef BLK_STAT_H
+#define BLK_STAT_H
+
+/*
+ * ~0.13s window as a power-of-2 (2^27 nsecs)
+ */
+#define BLK_STAT_NSEC	134217728ULL
+#define BLK_STAT_MASK	~(BLK_STAT_NSEC - 1)
+
+void blk_stat_add(struct blk_rq_stat *, struct request *);
+void blk_hctx_stat_get(struct blk_mq_hw_ctx *, struct blk_rq_stat *);
+void blk_queue_stat_get(struct request_queue *, struct blk_rq_stat *);
+void blk_stat_clear(struct request_queue *q);
+void blk_stat_init(struct blk_rq_stat *);
+void blk_stat_sum(struct blk_rq_stat *, struct blk_rq_stat *);
+bool blk_stat_is_current(struct blk_rq_stat *);
+
+#endif
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index f87a7e7..0b9e435 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -384,6 +384,26 @@ static ssize_t queue_dax_show(struct request_queue *q, char *page)
 	return queue_var_show(blk_queue_dax(q), page);
 }
 
+static ssize_t print_stat(char *page, struct blk_rq_stat *stat, const char *pre)
+{
+	return sprintf(page, "%s samples=%llu, mean=%lld, min=%lld, max=%lld\n",
+			pre, (long long) stat->nr_samples,
+			(long long) stat->mean, (long long) stat->min,
+			(long long) stat->max);
+}
+
+static ssize_t queue_stats_show(struct request_queue *q, char *page)
+{
+	struct blk_rq_stat stat[2];
+	ssize_t ret;
+
+	blk_queue_stat_get(q, stat);
+
+	ret = print_stat(page, &stat[0], "read :");
+	ret += print_stat(page + ret, &stat[1], "write:");
+	return ret;
+}
+
 static struct queue_sysfs_entry queue_requests_entry = {
 	.attr = {.name = "nr_requests", .mode = S_IRUGO | S_IWUSR },
 	.show = queue_requests_show,
@@ -526,6 +546,11 @@ static struct queue_sysfs_entry queue_dax_entry = {
 	.show = queue_dax_show,
 };
 
+static struct queue_sysfs_entry queue_stats_entry = {
+	.attr = {.name = "stats", .mode = S_IRUGO },
+	.show = queue_stats_show,
+};
+
 static struct attribute *default_attrs[] = {
 	&queue_requests_entry.attr,
 	&queue_ra_entry.attr,
@@ -553,6 +578,7 @@ static struct attribute *default_attrs[] = {
 	&queue_poll_entry.attr,
 	&queue_wc_entry.attr,
 	&queue_dax_entry.attr,
+	&queue_stats_entry.attr,
 	NULL,
 };
 
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index be4409b..95fbfa1 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -266,4 +266,16 @@ static inline unsigned int blk_qc_t_to_tag(blk_qc_t cookie)
 	return cookie & ((1u << BLK_QC_T_SHIFT) - 1);
 }
 
+#define BLK_RQ_STAT_BATCH	64
+
+struct blk_rq_stat {
+	s64 mean;
+	u64 min;
+	u64 max;
+	s32 nr_samples;
+	s32 nr_batch;
+	u64 batch;
+	s64 time;
+};
+
 #endif /* __LINUX_BLK_TYPES_H */
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 1d12aa6..259eba8 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -151,6 +151,7 @@ struct request {
 	struct gendisk *rq_disk;
 	struct hd_struct *part;
 	unsigned long start_time;
+	s64 issue_time;
 #ifdef CONFIG_BLK_CGROUP
 	struct request_list *rl;		/* rl this rq is alloced from */
 	unsigned long long start_time_ns;
@@ -414,6 +415,9 @@ struct request_queue {
 
 	unsigned int		nr_sorted;
 	unsigned int		in_flight[2];
+
+	struct blk_rq_stat	rq_stats[2];
+
 	/*
 	 * Number of active block driver functions for which blk_drain_queue()
 	 * must wait. Must be incremented around functions that unlock the
-- 
cgit v0.11.2

From 9a38b8e46f9f759dbb3fd81810579ac1013bf814 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@fb.com>
Date: Thu, 8 Sep 2016 11:07:16 -0600
Subject: wbt: add general throttling mechanism

We can hook this up to the block layer, to help throttle buffered
writes. Or NFS can tap into it, to accomplish the same.

wbt registers a few trace points that can be used to track what is
happening in the system:

wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
               wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32

This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.

Signed-off-by: Jens Axboe <axboe@fb.com>
---
 include/linux/wbt.h        | 120 ++++++++
 include/trace/events/wbt.h | 153 ++++++++++
 lib/Kconfig                |   3 +
 lib/Makefile               |   1 +
 lib/wbt.c                  | 681 +++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 958 insertions(+)
 create mode 100644 include/linux/wbt.h
 create mode 100644 include/trace/events/wbt.h
 create mode 100644 lib/wbt.c

diff --git a/include/linux/wbt.h b/include/linux/wbt.h
new file mode 100644
index 0000000..5ffcd14
--- /dev/null
+++ b/include/linux/wbt.h
@@ -0,0 +1,120 @@
+#ifndef WB_THROTTLE_H
+#define WB_THROTTLE_H
+
+#include <linux/atomic.h>
+#include <linux/wait.h>
+#include <linux/timer.h>
+#include <linux/ktime.h>
+
+enum {
+	ISSUE_STAT_TRACKED	= 1ULL << 63,
+	ISSUE_STAT_READ		= 1ULL << 62,
+	ISSUE_STAT_MASK 	= ISSUE_STAT_TRACKED | ISSUE_STAT_READ,
+	ISSUE_STAT_TIME_MASK	= ~ISSUE_STAT_MASK,
+
+	WBT_TRACKED		= 1,
+	WBT_READ		= 2,
+};
+
+struct wb_issue_stat {
+	u64 time;
+};
+
+static inline void wbt_issue_stat_set_time(struct wb_issue_stat *stat)
+{
+	stat->time = (stat->time & ISSUE_STAT_MASK) |
+			(ktime_to_ns(ktime_get()) & ISSUE_STAT_TIME_MASK);
+}
+
+static inline u64 wbt_issue_stat_get_time(struct wb_issue_stat *stat)
+{
+	return stat->time & ISSUE_STAT_TIME_MASK;
+}
+
+static inline void wbt_mark_tracked(struct wb_issue_stat *stat)
+{
+	stat->time |= ISSUE_STAT_TRACKED;
+}
+
+static inline void wbt_clear_state(struct wb_issue_stat *stat)
+{
+	stat->time &= ~(ISSUE_STAT_TRACKED | ISSUE_STAT_READ);
+}
+
+static inline bool wbt_tracked(struct wb_issue_stat *stat)
+{
+	return (stat->time & ISSUE_STAT_TRACKED) != 0;
+}
+
+static inline void wbt_mark_read(struct wb_issue_stat *stat)
+{
+	stat->time |= ISSUE_STAT_READ;
+}
+
+static inline bool wbt_is_read(struct wb_issue_stat *stat)
+{
+	return (stat->time & ISSUE_STAT_READ) != 0;
+}
+
+struct wb_stat_ops {
+	void (*get)(void *, struct blk_rq_stat *);
+	bool (*is_current)(struct blk_rq_stat *);
+	void (*clear)(void *);
+};
+
+struct rq_wb {
+	/*
+	 * Settings that govern how we throttle
+	 */
+	unsigned int wb_background;		/* background writeback */
+	unsigned int wb_normal;			/* normal writeback */
+	unsigned int wb_max;			/* max throughput writeback */
+	int scale_step;
+	bool scaled_max;
+
+	u64 win_nsec;				/* default window size */
+	u64 cur_win_nsec;			/* current window size */
+
+	/*
+	 * Number of consecutive periods where we don't have enough
+	 * information to make a firm scale up/down decision.
+	 */
+	unsigned int unknown_cnt;
+
+	struct timer_list window_timer;
+
+	s64 sync_issue;
+	void *sync_cookie;
+
+	unsigned int wc;
+	unsigned int queue_depth;
+
+	unsigned long last_issue;		/* last non-throttled issue */
+	unsigned long last_comp;		/* last non-throttled comp */
+	unsigned long min_lat_nsec;
+	struct backing_dev_info *bdi;
+	struct request_queue *q;
+	wait_queue_head_t wait;
+	atomic_t inflight;
+
+	struct wb_stat_ops *stat_ops;
+	void *ops_data;
+};
+
+struct backing_dev_info;
+
+void __wbt_done(struct rq_wb *);
+void wbt_done(struct rq_wb *, struct wb_issue_stat *);
+unsigned int wbt_wait(struct rq_wb *, unsigned int, spinlock_t *);
+struct rq_wb *wbt_init(struct backing_dev_info *, struct wb_stat_ops *, void *);
+void wbt_exit(struct rq_wb *);
+void wbt_update_limits(struct rq_wb *);
+void wbt_requeue(struct rq_wb *, struct wb_issue_stat *);
+void wbt_issue(struct rq_wb *, struct wb_issue_stat *);
+void wbt_disable(struct rq_wb *);
+void wbt_track(struct wb_issue_stat *, unsigned int);
+
+void wbt_set_queue_depth(struct rq_wb *, unsigned int);
+void wbt_set_write_cache(struct rq_wb *, bool);
+
+#endif
diff --git a/include/trace/events/wbt.h b/include/trace/events/wbt.h
new file mode 100644
index 0000000..926c7ee
--- /dev/null
+++ b/include/trace/events/wbt.h
@@ -0,0 +1,153 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM wbt
+
+#if !defined(_TRACE_WBT_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_WBT_H
+
+#include <linux/tracepoint.h>
+#include <linux/wbt.h>
+
+/**
+ * wbt_stat - trace stats for blk_wb
+ * @stat: array of read/write stats
+ */
+TRACE_EVENT(wbt_stat,
+
+	TP_PROTO(struct backing_dev_info *bdi, struct blk_rq_stat *stat),
+
+	TP_ARGS(bdi, stat),
+
+	TP_STRUCT__entry(
+		__array(char, name, 32)
+		__field(s64, rmean)
+		__field(u64, rmin)
+		__field(u64, rmax)
+		__field(s64, rnr_samples)
+		__field(s64, rtime)
+		__field(s64, wmean)
+		__field(u64, wmin)
+		__field(u64, wmax)
+		__field(s64, wnr_samples)
+		__field(s64, wtime)
+	),
+
+	TP_fast_assign(
+		strncpy(__entry->name, dev_name(bdi->dev), 32);
+		__entry->rmean		= stat[0].mean;
+		__entry->rmin		= stat[0].min;
+		__entry->rmax		= stat[0].max;
+		__entry->rnr_samples	= stat[0].nr_samples;
+		__entry->wmean		= stat[1].mean;
+		__entry->wmin		= stat[1].min;
+		__entry->wmax		= stat[1].max;
+		__entry->wnr_samples	= stat[1].nr_samples;
+	),
+
+	TP_printk("%s: rmean=%llu, rmin=%llu, rmax=%llu, rsamples=%llu, "
+		  "wmean=%llu, wmin=%llu, wmax=%llu, wsamples=%llu\n",
+		  __entry->name, __entry->rmean, __entry->rmin, __entry->rmax,
+		  __entry->rnr_samples, __entry->wmean, __entry->wmin,
+		  __entry->wmax, __entry->wnr_samples)
+);
+
+/**
+ * wbt_lat - trace latency event
+ * @lat: latency trigger
+ */
+TRACE_EVENT(wbt_lat,
+
+	TP_PROTO(struct backing_dev_info *bdi, unsigned long lat),
+
+	TP_ARGS(bdi, lat),
+
+	TP_STRUCT__entry(
+		__array(char, name, 32)
+		__field(unsigned long, lat)
+	),
+
+	TP_fast_assign(
+		strncpy(__entry->name, dev_name(bdi->dev), 32);
+		__entry->lat = div_u64(lat, 1000);
+	),
+
+	TP_printk("%s: latency %lluus\n", __entry->name,
+			(unsigned long long) __entry->lat)
+);
+
+/**
+ * wbt_step - trace wb event step
+ * @msg: context message
+ * @step: the current scale step count
+ * @window: the current monitoring window
+ * @bg: the current background queue limit
+ * @normal: the current normal writeback limit
+ * @max: the current max throughput writeback limit
+ */
+TRACE_EVENT(wbt_step,
+
+	TP_PROTO(struct backing_dev_info *bdi, const char *msg,
+		 int step, unsigned long window, unsigned int bg,
+		 unsigned int normal, unsigned int max),
+
+	TP_ARGS(bdi, msg, step, window, bg, normal, max),
+
+	TP_STRUCT__entry(
+		__array(char, name, 32)
+		__field(const char *, msg)
+		__field(int, step)
+		__field(unsigned long, window)
+		__field(unsigned int, bg)
+		__field(unsigned int, normal)
+		__field(unsigned int, max)
+	),
+
+	TP_fast_assign(
+		strncpy(__entry->name, dev_name(bdi->dev), 32);
+		__entry->msg	= msg;
+		__entry->step	= step;
+		__entry->window	= div_u64(window, 1000);
+		__entry->bg	= bg;
+		__entry->normal	= normal;
+		__entry->max	= max;
+	),
+
+	TP_printk("%s: %s: step=%d, window=%luus, background=%u, normal=%u, max=%u\n",
+		  __entry->name, __entry->msg, __entry->step, __entry->window,
+		  __entry->bg, __entry->normal, __entry->max)
+);
+
+/**
+ * wbt_timer - trace wb timer event
+ * @status: timer state status
+ * @step: the current scale step count
+ * @inflight: tracked writes inflight
+ */
+TRACE_EVENT(wbt_timer,
+
+	TP_PROTO(struct backing_dev_info *bdi, unsigned int status,
+		 int step, unsigned int inflight),
+
+	TP_ARGS(bdi, status, step, inflight),
+
+	TP_STRUCT__entry(
+		__array(char, name, 32)
+		__field(unsigned int, status)
+		__field(int, step)
+		__field(unsigned int, inflight)
+	),
+
+	TP_fast_assign(
+		strncpy(__entry->name, dev_name(bdi->dev), 32);
+		__entry->status		= status;
+		__entry->step		= step;
+		__entry->inflight	= inflight;
+	),
+
+	TP_printk("%s: status=%u, step=%d, inflight=%u\n", __entry->name,
+		  __entry->status, __entry->step, __entry->inflight)
+);
+
+#endif /* _TRACE_WBT_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/lib/Kconfig b/lib/Kconfig
index d79909d..c585e4c 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -550,4 +550,7 @@ config STACKDEPOT
 	bool
 	select STACKTRACE
 
+config WBT
+	bool
+
 endmenu
diff --git a/lib/Makefile b/lib/Makefile
index 5dc77a8..23afd63 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -177,6 +177,7 @@ obj-$(CONFIG_SG_SPLIT) += sg_split.o
 obj-$(CONFIG_SG_POOL) += sg_pool.o
 obj-$(CONFIG_STMP_DEVICE) += stmp_device.o
 obj-$(CONFIG_IRQ_POLL) += irq_poll.o
+obj-$(CONFIG_WBT) += wbt.o
 
 obj-$(CONFIG_STACKDEPOT) += stackdepot.o
 KASAN_SANITIZE_stackdepot.o := n
diff --git a/lib/wbt.c b/lib/wbt.c
new file mode 100644
index 0000000..a995703
--- /dev/null
+++ b/lib/wbt.c
@@ -0,0 +1,681 @@
+/*
+ * buffered writeback throttling. losely based on CoDel. We can't drop
+ * packets for IO scheduling, so the logic is something like this:
+ *
+ * - Monitor latencies in a defined window of time.
+ * - If the minimum latency in the above window exceeds some target, increment
+ *   scaling step and scale down queue depth by a factor of 2x. The monitoring
+ *   window is then shrunk to 100 / sqrt(scaling step + 1).
+ * - For any window where we don't have solid data on what the latencies
+ *   look like, retain status quo.
+ * - If latencies look good, decrement scaling step.
+ * - If we're only doing writes, allow the scaling step to go negative. This
+ *   will temporarily boost write performance, snapping back to a stable
+ *   scaling step of 0 if reads show up or the heavy writers finish. Unlike
+ *   positive scaling steps where we shrink the monitoring window, a negative
+ *   scaling step retains the default step==0 window size.
+ *
+ * Copyright (C) 2016 Jens Axboe
+ *
+ */
+#include <linux/kernel.h>
+#include <linux/blk_types.h>
+#include <linux/slab.h>
+#include <linux/backing-dev.h>
+#include <linux/wbt.h>
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/wbt.h>
+
+enum {
+	/*
+	 * Default setting, we'll scale up (to 75% of QD max) or down (min 1)
+	 * from here depending on device stats
+	 */
+	RWB_DEF_DEPTH	= 16,
+
+	/*
+	 * 100msec window
+	 */
+	RWB_WINDOW_NSEC		= 100 * 1000 * 1000ULL,
+
+	/*
+	 * Disregard stats, if we don't meet this minimum
+	 */
+	RWB_MIN_WRITE_SAMPLES	= 3,
+
+	/*
+	 * If we have this number of consecutive windows with not enough
+	 * information to scale up or down, scale up.
+	 */
+	RWB_UNKNOWN_BUMP	= 5,
+};
+
+static inline bool rwb_enabled(struct rq_wb *rwb)
+{
+	return rwb && rwb->wb_normal != 0;
+}
+
+/*
+ * Increment 'v', if 'v' is below 'below'. Returns true if we succeeded,
+ * false if 'v' + 1 would be bigger than 'below'.
+ */
+static bool atomic_inc_below(atomic_t *v, int below)
+{
+	int cur = atomic_read(v);
+
+	for (;;) {
+		int old;
+
+		if (cur >= below)
+			return false;
+		old = atomic_cmpxchg(v, cur, cur + 1);
+		if (old == cur)
+			break;
+		cur = old;
+	}
+
+	return true;
+}
+
+static void wb_timestamp(struct rq_wb *rwb, unsigned long *var)
+{
+	if (rwb_enabled(rwb)) {
+		const unsigned long cur = jiffies;
+
+		if (cur != *var)
+			*var = cur;
+	}
+}
+
+/*
+ * If a task was rate throttled in balance_dirty_pages() within the last
+ * second or so, use that to indicate a higher cleaning rate.
+ */
+static bool wb_recent_wait(struct rq_wb *rwb)
+{
+	struct bdi_writeback *wb = &rwb->bdi->wb;
+
+	return time_before(jiffies, wb->dirty_sleep + HZ);
+}
+
+void __wbt_done(struct rq_wb *rwb)
+{
+	int inflight, limit;
+
+	inflight = atomic_dec_return(&rwb->inflight);
+
+	/*
+	 * wbt got disabled with IO in flight. Wake up any potential
+	 * waiters, we don't have to do more than that.
+	 */
+	if (unlikely(!rwb_enabled(rwb))) {
+		wake_up_all(&rwb->wait);
+		return;
+	}
+
+	/*
+	 * If the device does write back caching, drop further down
+	 * before we wake people up.
+	 */
+	if (rwb->wc && !wb_recent_wait(rwb))
+		limit = 0;
+	else
+		limit = rwb->wb_normal;
+
+	/*
+	 * Don't wake anyone up if we are above the normal limit.
+	 */
+	if (inflight && inflight >= limit)
+		return;
+
+	if (waitqueue_active(&rwb->wait)) {
+		int diff = limit - inflight;
+
+		if (!inflight || diff >= rwb->wb_background / 2)
+			wake_up(&rwb->wait);
+	}
+}
+
+/*
+ * Called on completion of a request. Note that it's also called when
+ * a request is merged, when the request gets freed.
+ */
+void wbt_done(struct rq_wb *rwb, struct wb_issue_stat *stat)
+{
+	if (!rwb)
+		return;
+
+	if (!wbt_tracked(stat)) {
+		if (rwb->sync_cookie == stat) {
+			rwb->sync_issue = 0;
+			rwb->sync_cookie = NULL;
+		}
+
+		if (wbt_is_read(stat))
+			wb_timestamp(rwb, &rwb->last_comp);
+		wbt_clear_state(stat);
+	} else {
+		WARN_ON_ONCE(stat == rwb->sync_cookie);
+		__wbt_done(rwb);
+		wbt_clear_state(stat);
+	}
+}
+
+/*
+ * Return true, if we can't increase the depth further by scaling
+ */
+static bool calc_wb_limits(struct rq_wb *rwb)
+{
+	unsigned int depth;
+	bool ret = false;
+
+	if (!rwb->min_lat_nsec) {
+		rwb->wb_max = rwb->wb_normal = rwb->wb_background = 0;
+		return false;
+	}
+
+	/*
+	 * For QD=1 devices, this is a special case. It's important for those
+	 * to have one request ready when one completes, so force a depth of
+	 * 2 for those devices. On the backend, it'll be a depth of 1 anyway,
+	 * since the device can't have more than that in flight. If we're
+	 * scaling down, then keep a setting of 1/1/1.
+	 */
+	if (rwb->queue_depth == 1) {
+		if (rwb->scale_step > 0)
+			rwb->wb_max = rwb->wb_normal = 1;
+		else {
+			rwb->wb_max = rwb->wb_normal = 2;
+			ret = true;
+		}
+		rwb->wb_background = 1;
+	} else {
+		/*
+		 * scale_step == 0 is our default state. If we have suffered
+		 * latency spikes, step will be > 0, and we shrink the
+		 * allowed write depths. If step is < 0, we're only doing
+		 * writes, and we allow a temporarily higher depth to
+		 * increase performance.
+		 */
+		depth = min_t(unsigned int, RWB_DEF_DEPTH, rwb->queue_depth);
+		if (rwb->scale_step > 0)
+			depth = 1 + ((depth - 1) >> min(31, rwb->scale_step));
+		else if (rwb->scale_step < 0) {
+			unsigned int maxd = 3 * rwb->queue_depth / 4;
+
+			depth = 1 + ((depth - 1) << -rwb->scale_step);
+			if (depth > maxd) {
+				depth = maxd;
+				ret = true;
+			}
+		}
+
+		/*
+		 * Set our max/normal/bg queue depths based on how far
+		 * we have scaled down (->scale_step).
+		 */
+		rwb->wb_max = depth;
+		rwb->wb_normal = (rwb->wb_max + 1) / 2;
+		rwb->wb_background = (rwb->wb_max + 3) / 4;
+	}
+
+	return ret;
+}
+
+static bool inline stat_sample_valid(struct blk_rq_stat *stat)
+{
+	/*
+	 * We need at least one read sample, and a minimum of
+	 * RWB_MIN_WRITE_SAMPLES. We require some write samples to know
+	 * that it's writes impacting us, and not just some sole read on
+	 * a device that is in a lower power state.
+	 */
+	return stat[0].nr_samples >= 1 &&
+		stat[1].nr_samples >= RWB_MIN_WRITE_SAMPLES;
+}
+
+static u64 rwb_sync_issue_lat(struct rq_wb *rwb)
+{
+	u64 now, issue = ACCESS_ONCE(rwb->sync_issue);
+
+	if (!issue || !rwb->sync_cookie)
+		return 0;
+
+	now = ktime_to_ns(ktime_get());
+	return now - issue;
+}
+
+enum {
+	LAT_OK = 1,
+	LAT_UNKNOWN,
+	LAT_UNKNOWN_WRITES,
+	LAT_EXCEEDED,
+};
+
+static int __latency_exceeded(struct rq_wb *rwb, struct blk_rq_stat *stat)
+{
+	u64 thislat;
+
+	/*
+	 * If our stored sync issue exceeds the window size, or it
+	 * exceeds our min target AND we haven't logged any entries,
+	 * flag the latency as exceeded. wbt works off completion latencies,
+	 * but for a flooded device, a single sync IO can take a long time
+	 * to complete after being issued. If this time exceeds our
+	 * monitoring window AND we didn't see any other completions in that
+	 * window, then count that sync IO as a violation of the latency.
+	 */
+	thislat = rwb_sync_issue_lat(rwb);
+	if (thislat > rwb->cur_win_nsec ||
+	    (thislat > rwb->min_lat_nsec && !stat[0].nr_samples)) {
+		trace_wbt_lat(rwb->bdi, thislat);
+		return LAT_EXCEEDED;
+	}
+
+	/*
+	 * No read/write mix, if stat isn't valid
+	 */
+	if (!stat_sample_valid(stat)) {
+		/*
+		 * If we had writes in this stat window and the window is
+		 * current, we're only doing writes. If a task recently
+		 * waited or still has writes in flights, consider us doing
+		 * just writes as well.
+		 */
+		if ((stat[1].nr_samples && rwb->stat_ops->is_current(stat)) ||
+		    wb_recent_wait(rwb) || atomic_read(&rwb->inflight))
+			return LAT_UNKNOWN_WRITES;
+		return LAT_UNKNOWN;
+	}
+
+	/*
+	 * If the 'min' latency exceeds our target, step down.
+	 */
+	if (stat[0].min > rwb->min_lat_nsec) {
+		trace_wbt_lat(rwb->bdi, stat[0].min);
+		trace_wbt_stat(rwb->bdi, stat);
+		return LAT_EXCEEDED;
+	}
+
+	if (rwb->scale_step)
+		trace_wbt_stat(rwb->bdi, stat);
+
+	return LAT_OK;
+}
+
+static int latency_exceeded(struct rq_wb *rwb)
+{
+	struct blk_rq_stat stat[2];
+
+	rwb->stat_ops->get(rwb->ops_data, stat);
+	return __latency_exceeded(rwb, stat);
+}
+
+static void rwb_trace_step(struct rq_wb *rwb, const char *msg)
+{
+	trace_wbt_step(rwb->bdi, msg, rwb->scale_step, rwb->cur_win_nsec,
+			rwb->wb_background, rwb->wb_normal, rwb->wb_max);
+}
+
+static void scale_up(struct rq_wb *rwb)
+{
+	/*
+	 * Hit max in previous round, stop here
+	 */
+	if (rwb->scaled_max)
+		return;
+
+	rwb->scale_step--;
+	rwb->unknown_cnt = 0;
+	rwb->stat_ops->clear(rwb->ops_data);
+
+	rwb->scaled_max = calc_wb_limits(rwb);
+
+	if (waitqueue_active(&rwb->wait))
+		wake_up_all(&rwb->wait);
+
+	rwb_trace_step(rwb, "step up");
+}
+
+/*
+ * Scale rwb down. If 'hard_throttle' is set, do it quicker, since we
+ * had a latency violation.
+ */
+static void scale_down(struct rq_wb *rwb, bool hard_throttle)
+{
+	/*
+	 * Stop scaling down when we've hit the limit. This also prevents
+	 * ->scale_step from going to crazy values, if the device can't
+	 * keep up.
+	 */
+	if (rwb->wb_max == 1)
+		return;
+
+	if (rwb->scale_step < 0 && hard_throttle)
+		rwb->scale_step = 0;
+	else
+		rwb->scale_step++;
+
+	rwb->scaled_max = false;
+	rwb->unknown_cnt = 0;
+	rwb->stat_ops->clear(rwb->ops_data);
+	calc_wb_limits(rwb);
+	rwb_trace_step(rwb, "step down");
+}
+
+static void rwb_arm_timer(struct rq_wb *rwb)
+{
+	unsigned long expires;
+
+	if (rwb->scale_step > 0) {
+		/*
+		 * We should speed this up, using some variant of a fast
+		 * integer inverse square root calculation. Since we only do
+		 * this for every window expiration, it's not a huge deal,
+		 * though.
+		 */
+		rwb->cur_win_nsec = div_u64(rwb->win_nsec << 4,
+					int_sqrt((rwb->scale_step + 1) << 8));
+	} else {
+		/*
+		 * For step < 0, we don't want to increase/decrease the
+		 * window size.
+		 */
+		rwb->cur_win_nsec = rwb->win_nsec;
+	}
+
+	expires = jiffies + nsecs_to_jiffies(rwb->cur_win_nsec);
+	mod_timer(&rwb->window_timer, expires);
+}
+
+static void wb_timer_fn(unsigned long data)
+{
+	struct rq_wb *rwb = (struct rq_wb *) data;
+	int status, inflight;
+
+	inflight = atomic_read(&rwb->inflight);
+
+	status = latency_exceeded(rwb);
+
+	trace_wbt_timer(rwb->bdi, status, rwb->scale_step, inflight);
+
+	/*
+	 * If we exceeded the latency target, step down. If we did not,
+	 * step one level up. If we don't know enough to say either exceeded
+	 * or ok, then don't do anything.
+	 */
+	switch (status) {
+	case LAT_EXCEEDED:
+		scale_down(rwb, true);
+		break;
+	case LAT_OK:
+		scale_up(rwb);
+		break;
+	case LAT_UNKNOWN_WRITES:
+		scale_up(rwb);
+		break;
+	case LAT_UNKNOWN:
+		if (++rwb->unknown_cnt < RWB_UNKNOWN_BUMP)
+			break;
+		/*
+		 * We get here for two reasons:
+		 *
+		 * 1) We previously scaled reduced depth, and we currently
+		 *    don't have a valid read/write sample. For that case,
+		 *    slowly return to center state (step == 0).
+		 * 2) We started a the center step, but don't have a valid
+		 *    read/write sample, but we do have writes going on.
+		 *    Allow step to go negative, to increase write perf.
+		 */
+		if (rwb->scale_step > 0)
+			scale_up(rwb);
+		else if (rwb->scale_step < 0)
+			scale_down(rwb, false);
+		break;
+	default:
+		break;
+	}
+
+	/*
+	 * Re-arm timer, if we have IO in flight
+	 */
+	if (rwb->scale_step || inflight)
+		rwb_arm_timer(rwb);
+}
+
+void wbt_update_limits(struct rq_wb *rwb)
+{
+	rwb->scale_step = 0;
+	rwb->scaled_max = false;
+	calc_wb_limits(rwb);
+
+	if (waitqueue_active(&rwb->wait))
+		wake_up_all(&rwb->wait);
+}
+
+static bool close_io(struct rq_wb *rwb)
+{
+	const unsigned long now = jiffies;
+
+	return time_before(now, rwb->last_issue + HZ / 10) ||
+		time_before(now, rwb->last_comp + HZ / 10);
+}
+
+#define REQ_HIPRIO	(REQ_SYNC | REQ_META | REQ_PRIO)
+
+static inline unsigned int get_limit(struct rq_wb *rwb, unsigned long rw)
+{
+	unsigned int limit;
+
+	/*
+	 * At this point we know it's a buffered write. If REQ_SYNC is
+	 * set, then it's WB_SYNC_ALL writeback, and we'll use the max
+	 * limit for that. If the write is marked as a background write,
+	 * then use the idle limit, or go to normal if we haven't had
+	 * competing IO for a bit.
+	 */
+	if ((rw & REQ_HIPRIO) || wb_recent_wait(rwb))
+		limit = rwb->wb_max;
+	else if ((rw & REQ_BG) || close_io(rwb)) {
+		/*
+		 * If less than 100ms since we completed unrelated IO,
+		 * limit us to half the depth for background writeback.
+		 */
+		limit = rwb->wb_background;
+	} else
+		limit = rwb->wb_normal;
+
+	return limit;
+}
+
+static inline bool may_queue(struct rq_wb *rwb, unsigned long rw)
+{
+	/*
+	 * inc it here even if disabled, since we'll dec it at completion.
+	 * this only happens if the task was sleeping in __wbt_wait(),
+	 * and someone turned it off at the same time.
+	 */
+	if (!rwb_enabled(rwb)) {
+		atomic_inc(&rwb->inflight);
+		return true;
+	}
+
+	return atomic_inc_below(&rwb->inflight, get_limit(rwb, rw));
+}
+
+/*
+ * Block if we will exceed our limit, or if we are currently waiting for
+ * the timer to kick off queuing again.
+ */
+static void __wbt_wait(struct rq_wb *rwb, unsigned long rw, spinlock_t *lock)
+{
+	DEFINE_WAIT(wait);
+
+	if (may_queue(rwb, rw))
+		return;
+
+	do {
+		prepare_to_wait_exclusive(&rwb->wait, &wait,
+						TASK_UNINTERRUPTIBLE);
+
+		if (may_queue(rwb, rw))
+			break;
+
+		if (lock)
+			spin_unlock_irq(lock);
+
+		io_schedule();
+
+		if (lock)
+			spin_lock_irq(lock);
+	} while (1);
+
+	finish_wait(&rwb->wait, &wait);
+}
+
+static inline bool wbt_should_throttle(struct rq_wb *rwb, unsigned int rw)
+{
+	const int op = rw >> BIO_OP_SHIFT;
+
+	/*
+	 * If not a WRITE (or a discard), do nothing
+	 */
+	if (!(op == REQ_OP_WRITE || op == REQ_OP_DISCARD))
+		return false;
+
+	/*
+	 * Don't throttle WRITE_ODIRECT
+	 */
+	if ((rw & (REQ_SYNC | REQ_NOIDLE)) == REQ_SYNC)
+		return false;
+
+	return true;
+}
+
+/*
+ * Returns true if the IO request should be accounted, false if not.
+ * May sleep, if we have exceeded the writeback limits. Caller can pass
+ * in an irq held spinlock, if it holds one when calling this function.
+ * If we do sleep, we'll release and re-grab it.
+ */
+unsigned int wbt_wait(struct rq_wb *rwb, unsigned int rw, spinlock_t *lock)
+{
+	unsigned int ret;
+
+	if (!rwb_enabled(rwb))
+		return 0;
+
+	if ((rw >> BIO_OP_SHIFT) == REQ_OP_READ)
+		ret = WBT_READ;
+
+	if (!wbt_should_throttle(rwb, rw)) {
+		if (ret & WBT_READ)
+			wb_timestamp(rwb, &rwb->last_issue);
+		return ret;
+	}
+
+	__wbt_wait(rwb, rw, lock);
+
+	if (!timer_pending(&rwb->window_timer))
+		rwb_arm_timer(rwb);
+
+	return ret | WBT_TRACKED;
+}
+
+void wbt_issue(struct rq_wb *rwb, struct wb_issue_stat *stat)
+{
+	if (!rwb_enabled(rwb))
+		return;
+
+	wbt_issue_stat_set_time(stat);
+
+	/*
+	 * Track sync issue, in case it takes a long time to complete. Allows
+	 * us to react quicker, if a sync IO takes a long time to complete.
+	 * Note that this is just a hint. 'stat' can go away when the
+	 * request completes, so it's important we never dereference it. We
+	 * only use the address to compare with, which is why we store the
+	 * sync_issue time locally.
+	 */
+	if (wbt_is_read(stat) && !rwb->sync_issue) {
+		rwb->sync_cookie = stat;
+		rwb->sync_issue = wbt_issue_stat_get_time(stat);
+	}
+}
+
+void wbt_track(struct wb_issue_stat *stat, unsigned int wb_acct)
+{
+	if (wb_acct & WBT_TRACKED)
+		wbt_mark_tracked(stat);
+	else if (wb_acct & WBT_READ)
+		wbt_mark_read(stat);
+}
+
+void wbt_requeue(struct rq_wb *rwb, struct wb_issue_stat *stat)
+{
+	if (!rwb_enabled(rwb))
+		return;
+	if (stat == rwb->sync_cookie) {
+		rwb->sync_issue = 0;
+		rwb->sync_cookie = NULL;
+	}
+}
+
+void wbt_set_queue_depth(struct rq_wb *rwb, unsigned int depth)
+{
+	if (rwb) {
+		rwb->queue_depth = depth;
+		wbt_update_limits(rwb);
+	}
+}
+
+void wbt_set_write_cache(struct rq_wb *rwb, bool write_cache_on)
+{
+	if (rwb)
+		rwb->wc = write_cache_on;
+}
+
+void wbt_disable(struct rq_wb *rwb)
+{
+	if (rwb) {
+		del_timer_sync(&rwb->window_timer);
+		rwb->win_nsec = rwb->min_lat_nsec = 0;
+		wbt_update_limits(rwb);
+	}
+}
+EXPORT_SYMBOL_GPL(wbt_disable);
+
+struct rq_wb *wbt_init(struct backing_dev_info *bdi, struct wb_stat_ops *ops,
+		       void *ops_data)
+{
+	struct rq_wb *rwb;
+
+	if (!ops->get || !ops->is_current || !ops->clear)
+		return ERR_PTR(-EINVAL);
+
+	rwb = kzalloc(sizeof(*rwb), GFP_KERNEL);
+	if (!rwb)
+		return ERR_PTR(-ENOMEM);
+
+	atomic_set(&rwb->inflight, 0);
+	init_waitqueue_head(&rwb->wait);
+	setup_timer(&rwb->window_timer, wb_timer_fn, (unsigned long) rwb);
+	rwb->wc = 1;
+	rwb->queue_depth = RWB_DEF_DEPTH;
+	rwb->last_comp = rwb->last_issue = jiffies;
+	rwb->bdi = bdi;
+	rwb->win_nsec = RWB_WINDOW_NSEC;
+	rwb->stat_ops = ops,
+	rwb->ops_data = ops_data;
+	wbt_update_limits(rwb);
+	return rwb;
+}
+
+void wbt_exit(struct rq_wb *rwb)
+{
+	if (rwb) {
+		del_timer_sync(&rwb->window_timer);
+		kfree(rwb);
+	}
+}
-- 
cgit v0.11.2

From db3de07314ef350fceb90ade08474fe4eea5e665 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@fb.com>
Date: Thu, 8 Sep 2016 11:08:17 -0600
Subject: writeback: throttle buffered writeback

Test patch that throttles buffered writeback to make it a lot
more smooth, and has way less impact on other system activity.
Background writeback should be, by definition, background
activity. The fact that we flush huge bundles of it at the time
means that it potentially has heavy impacts on foreground workloads,
which isn't ideal. We can't easily limit the sizes of writes that
we do, since that would impact file system layout in the presence
of delayed allocation. So just throttle back buffered writeback,
unless someone is waiting for it.

The algorithm for when to throttle takes its inspiration in the
CoDel networking scheduling algorithm. Like CoDel, blk-wb monitors
the minimum latencies of requests over a window of time. In that
window of time, if the minimum latency of any request exceeds a
given target, then a scale count is incremented and the queue depth
is shrunk. The next monitoring window is shrunk accordingly. Unlike
CoDel, if we hit a window that exhibits good behavior, then we
simply increment the scale count and re-calculate the limits for that
scale value. This prevents us from oscillating between a
close-to-ideal value and max all the time, instead remaining in the
windows where we get good behavior.

Unlike CoDel, blk-wb allows the scale count to to negative. This
happens if we primarily have writes going on. Unlike positive
scale counts, this doesn't change the size of the monitoring window.
When the heavy writers finish, blk-bw quickly snaps back to it's
stable state of a zero scale count.

The patch registers two sysfs entries. The first one, 'wb_window_usec',
defines the window of monitoring. The second one, 'wb_lat_usec',
sets the latency target for the window. It defaults to 2 msec for
non-rotational storage, and 75 msec for rotational storage. Setting
this value to '0' disables blk-wb. Generally, a user would not have
to touch these settings.

We don't enable WBT on devices that are managed with CFQ, and have
a non-root block cgroup attached. If we have a proportional share setup
on this particular disk, then the wbt throttling will interfere with
that. We don't have a strong need for wbt for that case, since we will
rely on CFQ doing that for us.

Signed-off-by: Jens Axboe <axboe@fb.com>
---
 Documentation/block/queue-sysfs.txt |  13 ++++
 block/Kconfig                       |   1 +
 block/blk-core.c                    |  20 +++++-
 block/blk-mq.c                      |  30 ++++++++-
 block/blk-settings.c                |   3 +
 block/blk-stat.c                    |   5 +-
 block/blk-sysfs.c                   | 125 ++++++++++++++++++++++++++++++++++++
 block/cfq-iosched.c                 |  13 ++++
 include/linux/blkdev.h              |   6 +-
 9 files changed, 207 insertions(+), 9 deletions(-)

diff --git a/Documentation/block/queue-sysfs.txt b/Documentation/block/queue-sysfs.txt
index 2a39040..2847219 100644
--- a/Documentation/block/queue-sysfs.txt
+++ b/Documentation/block/queue-sysfs.txt
@@ -169,5 +169,18 @@ This is the number of bytes the device can write in a single write-same
 command.  A value of '0' means write-same is not supported by this
 device.
 
+wb_lat_usec (RW)
+----------------
+If the device is registered for writeback throttling, then this file shows
+the target minimum read latency. If this latency is exceeded in a given
+window of time (see wb_window_usec), then the writeback throttling will start
+scaling back writes.
+
+wb_window_usec (RW)
+-------------------
+If the device is registered for writeback throttling, then this file shows
+the value of the monitoring window in which we'll look at the target
+latency. See wb_lat_usec.
+
 
 Jens Axboe <jens.axboe@oracle.com>, February 2009
diff --git a/block/Kconfig b/block/Kconfig
index 161491d..6da79e6 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -4,6 +4,7 @@
 menuconfig BLOCK
        bool "Enable the block layer" if EXPERT
        default y
+       select WBT
        help
 	 Provide block layer support for the kernel.
 
diff --git a/block/blk-core.c b/block/blk-core.c
index 4075cbe..4f4ce05 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -33,6 +33,7 @@
 #include <linux/ratelimit.h>
 #include <linux/pm_runtime.h>
 #include <linux/blk-cgroup.h>
+#include <linux/wbt.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/block.h>
@@ -882,6 +883,8 @@ blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,
 
 fail:
 	blk_free_flush_queue(q->fq);
+	wbt_exit(q->rq_wb);
+	q->rq_wb = NULL;
 	return NULL;
 }
 EXPORT_SYMBOL(blk_init_allocated_queue);
@@ -1346,6 +1349,7 @@ void blk_requeue_request(struct request_queue *q, struct request *rq)
 	blk_delete_timer(rq);
 	blk_clear_rq_complete(rq);
 	trace_block_rq_requeue(q, rq);
+	wbt_requeue(q->rq_wb, &rq->wb_stat);
 
 	if (rq->cmd_flags & REQ_QUEUED)
 		blk_queue_end_tag(q, rq);
@@ -1436,6 +1440,8 @@ void __blk_put_request(struct request_queue *q, struct request *req)
 	/* this is a bio leak */
 	WARN_ON(req->bio != NULL);
 
+	wbt_done(q->rq_wb, &req->wb_stat);
+
 	/*
 	 * Request may not have originated from ll_rw_blk. if not,
 	 * it didn't come out of our reserved rq pools
@@ -1667,6 +1673,7 @@ static blk_qc_t blk_queue_bio(struct request_queue *q, struct bio *bio)
 	int el_ret, rw_flags = 0, where = ELEVATOR_INSERT_SORT;
 	struct request *req;
 	unsigned int request_count = 0;
+	unsigned int wb_acct;
 
 	/*
 	 * low level driver can indicate that it wants pages above a
@@ -1719,6 +1726,8 @@ static blk_qc_t blk_queue_bio(struct request_queue *q, struct bio *bio)
 	}
 
 get_rq:
+	wb_acct = wbt_wait(q->rq_wb, bio->bi_opf, q->queue_lock);
+
 	/*
 	 * This sync check and mask will be re-done in init_request_from_bio(),
 	 * but we need to set it earlier to expose the sync flag to the
@@ -1738,11 +1747,15 @@ get_rq:
 	 */
 	req = get_request(q, bio_data_dir(bio), rw_flags, bio, GFP_NOIO);
 	if (IS_ERR(req)) {
+		if (wb_acct & WBT_TRACKED)
+			__wbt_done(q->rq_wb);
 		bio->bi_error = PTR_ERR(req);
 		bio_endio(bio);
 		goto out_unlock;
 	}
 
+	wbt_track(&req->wb_stat, wb_acct);
+
 	/*
 	 * After dropping the lock and possibly sleeping here, our request
 	 * may now be mergeable after it had proven unmergeable (above).
@@ -2475,7 +2488,7 @@ void blk_start_request(struct request *req)
 {
 	blk_dequeue_request(req);
 
-	req->issue_time = ktime_to_ns(ktime_get());
+	wbt_issue(req->q->rq_wb, &req->wb_stat);
 
 	/*
 	 * We are now handing the request to the hardware, initialize
@@ -2713,9 +2726,10 @@ void blk_finish_request(struct request *req, int error)
 
 	blk_account_io_done(req);
 
-	if (req->end_io)
+	if (req->end_io) {
+		wbt_done(req->q->rq_wb, &req->wb_stat);
 		req->end_io(req, error);
-	else {
+	} else {
 		if (blk_bidi_rq(req))
 			__blk_put_request(req->next_rq->q, req->next_rq);
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 712f141..511289a 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -22,6 +22,7 @@
 #include <linux/sched/sysctl.h>
 #include <linux/delay.h>
 #include <linux/crash_dump.h>
+#include <linux/wbt.h>
 
 #include <trace/events/block.h>
 
@@ -319,6 +320,8 @@ static void __blk_mq_free_request(struct blk_mq_hw_ctx *hctx,
 
 	if (rq->cmd_flags & REQ_MQ_INFLIGHT)
 		atomic_dec(&hctx->nr_active);
+
+	wbt_done(q->rq_wb, &rq->wb_stat);
 	rq->cmd_flags = 0;
 
 	clear_bit(REQ_ATOM_STARTED, &rq->atomic_flags);
@@ -351,6 +354,7 @@ inline void __blk_mq_end_request(struct request *rq, int error)
 	blk_account_io_done(rq);
 
 	if (rq->end_io) {
+		wbt_done(rq->q->rq_wb, &rq->wb_stat);
 		rq->end_io(rq, error);
 	} else {
 		if (unlikely(blk_bidi_rq(rq)))
@@ -457,7 +461,7 @@ void blk_mq_start_request(struct request *rq)
 	if (unlikely(blk_bidi_rq(rq)))
 		rq->next_rq->resid_len = blk_rq_bytes(rq->next_rq);
 
-	rq->issue_time = ktime_to_ns(ktime_get());
+	wbt_issue(q->rq_wb, &rq->wb_stat);
 
 	blk_add_timer(rq);
 
@@ -494,6 +498,7 @@ static void __blk_mq_requeue_request(struct request *rq)
 	struct request_queue *q = rq->q;
 
 	trace_block_rq_requeue(q, rq);
+	wbt_requeue(q->rq_wb, &rq->wb_stat);
 
 	if (test_and_clear_bit(REQ_ATOM_STARTED, &rq->atomic_flags)) {
 		if (q->dma_drain_size && blk_rq_bytes(rq))
@@ -1312,6 +1317,7 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 	struct blk_plug *plug;
 	struct request *same_queue_rq = NULL;
 	blk_qc_t cookie;
+	unsigned int wb_acct;
 
 	blk_queue_bounce(q, &bio);
 
@@ -1326,9 +1332,16 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 	    blk_attempt_plug_merge(q, bio, &request_count, &same_queue_rq))
 		return BLK_QC_T_NONE;
 
+	wb_acct = wbt_wait(q->rq_wb, bio->bi_opf, NULL);
+
 	rq = blk_mq_map_request(q, bio, &data);
-	if (unlikely(!rq))
+	if (unlikely(!rq)) {
+		if (wb_acct & WBT_TRACKED)
+			__wbt_done(q->rq_wb);
 		return BLK_QC_T_NONE;
+	}
+
+	wbt_track(&rq->wb_stat, wb_acct);
 
 	cookie = blk_tag_to_qc_t(rq->tag, data.hctx->queue_num);
 
@@ -1405,6 +1418,7 @@ static blk_qc_t blk_sq_make_request(struct request_queue *q, struct bio *bio)
 	struct blk_map_ctx data;
 	struct request *rq;
 	blk_qc_t cookie;
+	unsigned int wb_acct;
 
 	blk_queue_bounce(q, &bio);
 
@@ -1421,9 +1435,16 @@ static blk_qc_t blk_sq_make_request(struct request_queue *q, struct bio *bio)
 	} else
 		request_count = blk_plug_queued_count(q);
 
+	wb_acct = wbt_wait(q->rq_wb, bio->bi_opf, NULL);
+
 	rq = blk_mq_map_request(q, bio, &data);
-	if (unlikely(!rq))
+	if (unlikely(!rq)) {
+		if (wb_acct & WBT_TRACKED)
+			__wbt_done(q->rq_wb);
 		return BLK_QC_T_NONE;
+	}
+
+	wbt_track(&rq->wb_stat, wb_acct);
 
 	cookie = blk_tag_to_qc_t(rq->tag, data.hctx->queue_num);
 
@@ -2147,6 +2168,9 @@ void blk_mq_free_queue(struct request_queue *q)
 	list_del_init(&q->all_q_node);
 	mutex_unlock(&all_q_mutex);
 
+	wbt_exit(q->rq_wb);
+	q->rq_wb = NULL;
+
 	blk_mq_del_queue_tag_set(q);
 
 	blk_mq_exit_hw_queues(q, set, set->nr_hw_queues);
diff --git a/block/blk-settings.c b/block/blk-settings.c
index f7e122e..746dc9f 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -840,6 +840,7 @@ EXPORT_SYMBOL_GPL(blk_queue_flush_queueable);
 void blk_set_queue_depth(struct request_queue *q, unsigned int depth)
 {
 	q->queue_depth = depth;
+	wbt_set_queue_depth(q->rq_wb, depth);
 }
 EXPORT_SYMBOL(blk_set_queue_depth);
 
@@ -863,6 +864,8 @@ void blk_queue_write_cache(struct request_queue *q, bool wc, bool fua)
 	else
 		queue_flag_clear(QUEUE_FLAG_FUA, q);
 	spin_unlock_irq(q->queue_lock);
+
+	wbt_set_write_cache(q->rq_wb, test_bit(QUEUE_FLAG_WC, &q->queue_flags));
 }
 EXPORT_SYMBOL_GPL(blk_queue_write_cache);
 
diff --git a/block/blk-stat.c b/block/blk-stat.c
index 3965e8a..bdb16d8 100644
--- a/block/blk-stat.c
+++ b/block/blk-stat.c
@@ -178,15 +178,16 @@ bool blk_stat_is_current(struct blk_rq_stat *stat)
 void blk_stat_add(struct blk_rq_stat *stat, struct request *rq)
 {
 	s64 now, value;
+	u64 rq_time = wbt_issue_stat_get_time(&rq->wb_stat);
 
 	now = ktime_to_ns(ktime_get());
-	if (now < rq->issue_time)
+	if (now < rq_time)
 		return;
 
 	if (!__blk_stat_is_current(stat, now))
 		__blk_stat_init(stat, now);
 
-	value = now - rq->issue_time;
+	value = now - rq_time;
 	if (value > stat->max)
 		stat->max = value;
 	if (value < stat->min)
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 0b9e435..85c3dc2 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -10,6 +10,7 @@
 #include <linux/blktrace_api.h>
 #include <linux/blk-mq.h>
 #include <linux/blk-cgroup.h>
+#include <linux/wbt.h>
 
 #include "blk.h"
 #include "blk-mq.h"
@@ -41,6 +42,19 @@ queue_var_store(unsigned long *var, const char *page, size_t count)
 	return count;
 }
 
+static ssize_t queue_var_store64(u64 *var, const char *page)
+{
+	int err;
+	u64 v;
+
+	err = kstrtou64(page, 10, &v);
+	if (err < 0)
+		return err;
+
+	*var = v;
+	return 0;
+}
+
 static ssize_t queue_requests_show(struct request_queue *q, char *page)
 {
 	return queue_var_show(q->nr_requests, (page));
@@ -347,6 +361,58 @@ static ssize_t queue_poll_store(struct request_queue *q, const char *page,
 	return ret;
 }
 
+static ssize_t queue_wb_win_show(struct request_queue *q, char *page)
+{
+	if (!q->rq_wb)
+		return -EINVAL;
+
+	return sprintf(page, "%llu\n", div_u64(q->rq_wb->win_nsec, 1000));
+}
+
+static ssize_t queue_wb_win_store(struct request_queue *q, const char *page,
+				  size_t count)
+{
+	ssize_t ret;
+	u64 val;
+
+	if (!q->rq_wb)
+		return -EINVAL;
+
+	ret = queue_var_store64(&val, page);
+	if (ret < 0)
+		return ret;
+
+	q->rq_wb->win_nsec = val * 1000ULL;
+	wbt_update_limits(q->rq_wb);
+	return count;
+}
+
+static ssize_t queue_wb_lat_show(struct request_queue *q, char *page)
+{
+	if (!q->rq_wb)
+		return -EINVAL;
+
+	return sprintf(page, "%llu\n", div_u64(q->rq_wb->min_lat_nsec, 1000));
+}
+
+static ssize_t queue_wb_lat_store(struct request_queue *q, const char *page,
+				  size_t count)
+{
+	ssize_t ret;
+	u64 val;
+
+	if (!q->rq_wb)
+		return -EINVAL;
+
+	ret = queue_var_store64(&val, page);
+	if (ret < 0)
+		return ret;
+
+	q->rq_wb->min_lat_nsec = val * 1000ULL;
+	wbt_update_limits(q->rq_wb);
+	return count;
+}
+
 static ssize_t queue_wc_show(struct request_queue *q, char *page)
 {
 	if (test_bit(QUEUE_FLAG_WC, &q->queue_flags))
@@ -551,6 +617,18 @@ static struct queue_sysfs_entry queue_stats_entry = {
 	.show = queue_stats_show,
 };
 
+static struct queue_sysfs_entry queue_wb_lat_entry = {
+	.attr = {.name = "wbt_lat_usec", .mode = S_IRUGO | S_IWUSR },
+	.show = queue_wb_lat_show,
+	.store = queue_wb_lat_store,
+};
+
+static struct queue_sysfs_entry queue_wb_win_entry = {
+	.attr = {.name = "wbt_window_usec", .mode = S_IRUGO | S_IWUSR },
+	.show = queue_wb_win_show,
+	.store = queue_wb_win_store,
+};
+
 static struct attribute *default_attrs[] = {
 	&queue_requests_entry.attr,
 	&queue_ra_entry.attr,
@@ -579,6 +657,8 @@ static struct attribute *default_attrs[] = {
 	&queue_wc_entry.attr,
 	&queue_dax_entry.attr,
 	&queue_stats_entry.attr,
+	&queue_wb_lat_entry.attr,
+	&queue_wb_win_entry.attr,
 	NULL,
 };
 
@@ -693,6 +773,49 @@ struct kobj_type blk_queue_ktype = {
 	.release	= blk_release_queue,
 };
 
+static void blk_wb_stat_get(void *data, struct blk_rq_stat *stat)
+{
+	blk_queue_stat_get(data, stat);
+}
+
+static void blk_wb_stat_clear(void *data)
+{
+	blk_stat_clear(data);
+}
+
+static bool blk_wb_stat_is_current(struct blk_rq_stat *stat)
+{
+	return blk_stat_is_current(stat);
+}
+
+static struct wb_stat_ops wb_stat_ops = {
+	.get		= blk_wb_stat_get,
+	.is_current	= blk_wb_stat_is_current,
+	.clear		= blk_wb_stat_clear,
+};
+
+static void blk_wb_init(struct request_queue *q)
+{
+	struct rq_wb *rwb;
+
+	rwb = wbt_init(&q->backing_dev_info, &wb_stat_ops, q);
+
+	/*
+	 * If this fails, we don't get throttling
+	 */
+	if (IS_ERR(rwb))
+		return;
+
+	if (blk_queue_nonrot(q))
+		rwb->min_lat_nsec = 2000000ULL;
+	else
+		rwb->min_lat_nsec = 75000000ULL;
+
+	wbt_set_queue_depth(rwb, blk_queue_depth(q));
+	wbt_set_write_cache(rwb, test_bit(QUEUE_FLAG_WC, &q->queue_flags));
+	q->rq_wb = rwb;
+}
+
 int blk_register_queue(struct gendisk *disk)
 {
 	int ret;
@@ -732,6 +855,8 @@ int blk_register_queue(struct gendisk *disk)
 	if (q->mq_ops)
 		blk_mq_register_disk(disk);
 
+	blk_wb_init(q);
+
 	if (!q->request_fn)
 		return 0;
 
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index cc2f6db..fdcd5999 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3764,9 +3764,11 @@ static void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
 	struct cfq_data *cfqd = cic_to_cfqd(cic);
 	struct cfq_queue *cfqq;
 	uint64_t serial_nr;
+	bool nonroot_cg;
 
 	rcu_read_lock();
 	serial_nr = bio_blkcg(bio)->css.serial_nr;
+	nonroot_cg = bio_blkcg(bio) != &blkcg_root;
 	rcu_read_unlock();
 
 	/*
@@ -3777,6 +3779,17 @@ static void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
 		return;
 
 	/*
+	 * If we have a non-root cgroup, we can depend on that to
+	 * do proper throttling of writes. Turn off wbt for that
+	 * case.
+	 */
+	if (nonroot_cg) {
+		struct request_queue *q = cfqd->queue;
+
+		wbt_disable(q->rq_wb);
+	}
+
+	/*
 	 * Drop reference to queues.  New queues will be assigned in new
 	 * group upon arrival of fresh requests.
 	 */
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 259eba8..45256d7 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -24,6 +24,7 @@
 #include <linux/rcupdate.h>
 #include <linux/percpu-refcount.h>
 #include <linux/scatterlist.h>
+#include <linux/wbt.h>
 
 struct module;
 struct scsi_ioctl_command;
@@ -37,6 +38,7 @@ struct bsg_job;
 struct blkcg_gq;
 struct blk_flush_queue;
 struct pr_ops;
+struct rq_wb;
 
 #define BLKDEV_MIN_RQ	4
 #define BLKDEV_MAX_RQ	128	/* Default maximum */
@@ -151,7 +153,7 @@ struct request {
 	struct gendisk *rq_disk;
 	struct hd_struct *part;
 	unsigned long start_time;
-	s64 issue_time;
+	struct wb_issue_stat wb_stat;
 #ifdef CONFIG_BLK_CGROUP
 	struct request_list *rl;		/* rl this rq is alloced from */
 	unsigned long long start_time_ns;
@@ -303,6 +305,8 @@ struct request_queue {
 	int			nr_rqs[2];	/* # allocated [a]sync rqs */
 	int			nr_rqs_elvpriv;	/* # allocated rqs w/ elvpriv */
 
+	struct rq_wb		*rq_wb;
+
 	/*
 	 * If blkcg is not used, @q->root_rl serves all requests.  If blkcg
 	 * is used, root blkg allocates from @q->root_rl and all other
-- 
cgit v0.11.2

From 21c990f3ab1d3324ad3152cb94f86e6e0772b73c Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@fb.com>
Date: Sat, 10 Sep 2016 10:06:26 -0600
Subject: wbt: spelling check fix

Signed-off-by: Jens Axboe <axboe@fb.com>
---
 lib/wbt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/wbt.c b/lib/wbt.c
index a995703..5c507e5 100644
--- a/lib/wbt.c
+++ b/lib/wbt.c
@@ -1,5 +1,5 @@
 /*
- * buffered writeback throttling. losely based on CoDel. We can't drop
+ * buffered writeback throttling. loosely based on CoDel. We can't drop
  * packets for IO scheduling, so the logic is something like this:
  *
  * - Monitor latencies in a defined window of time.
-- 
cgit v0.11.2