Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/shli/md

Pull md updates from Shaohua Li:
 "Mainly fixes bugs and improves performance:

   - Improve scalability for raid1 from Coly

   - Improve raid5-cache read performance, disk efficiency and IO
     pattern from Song and me

   - Fix a race condition of disk hotplug for linear from Coly

   - A few cleanup patches from Ming and Byungchul

   - Fix a memory leak from Neil

   - Fix WRITE SAME IO failure from me

   - Add doc for raid5-cache from me"

* 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/shli/md: (23 commits)
  md/raid1: fix write behind issues introduced by bio_clone_bioset_partial
  md/raid1: handle flush request correctly
  md/linear: shutup lockdep warnning
  md/raid1: fix a use-after-free bug
  RAID1: avoid unnecessary spin locks in I/O barrier code
  RAID1: a new I/O barrier implementation to remove resync window
  md/raid5: Don't reinvent the wheel but use existing llist API
  md: fast clone bio in bio_clone_mddev()
  md: remove unnecessary check on mddev
  md/raid1: use bio_clone_bioset_partial() in case of write behind
  md: fail if mddev->bio_set can't be created
  block: introduce bio_clone_bioset_partial()
  md: disable WRITE SAME if it fails in underlayer disks
  md/raid5-cache: exclude reclaiming stripes in reclaim check
  md/raid5-cache: stripe reclaim only counts valid stripes
  MD: add doc for raid5-cache
  Documentation: move MD related doc into a separate dir
  md: ensure md devices are freed before module is unloaded.
  md/r5cache: improve journal device efficiency
  md/r5cache: enable chunk_aligned_read with write back cache
  ...

Documentation/00-INDEX

@@ -270,8 +270,8 @@ m68k/
 	- directory with info about Linux on Motorola 68k architecture.
 mailbox.txt
 	- How to write drivers for the common mailbox framework (IPC).
-md-cluster.txt
-	- info on shared-device RAID MD cluster.
+md/
+	- directory with info about Linux Software RAID
 media/
 	- info on media drivers: uAPI, kAPI and driver documentation.
 memory-barriers.txt

Documentation/admin-guide/md.rst

@@ -725,3 +725,8 @@ These currently include:
       to 1.  Setting this to 0 disables bypass accounting and
       requires preread stripes to wait until all full-width stripe-
       writes are complete.  Valid values are 0 to stripe_cache_size.
+
+  journal_mode (currently raid5 only)
+      The cache mode for raid5. raid5 could include an extra disk for
+      caching. The mode can be "write-throuth" and "write-back". The
+      default is "write-through".

Documentation/md/raid5-cache.txt

+RAID5 cache
+
+Raid 4/5/6 could include an extra disk for data cache besides normal RAID
+disks. The role of RAID disks isn't changed with the cache disk. The cache disk
+caches data to the RAID disks. The cache can be in write-through (supported
+since 4.4) or write-back mode (supported since 4.10). mdadm (supported since
+3.4) has a new option '--write-journal' to create array with cache. Please
+refer to mdadm manual for details. By default (RAID array starts), the cache is
+in write-through mode. A user can switch it to write-back mode by:
+
+echo "write-back" > /sys/block/md0/md/journal_mode
+
+And switch it back to write-through mode by:
+
+echo "write-through" > /sys/block/md0/md/journal_mode
+
+In both modes, all writes to the array will hit cache disk first. This means
+the cache disk must be fast and sustainable.
+
+-------------------------------------
+write-through mode:
+
+This mode mainly fixes the 'write hole' issue. For RAID 4/5/6 array, an unclean
+shutdown can cause data in some stripes to not be in consistent state, eg, data
+and parity don't match. The reason is that a stripe write involves several RAID
+disks and it's possible the writes don't hit all RAID disks yet before the
+unclean shutdown. We call an array degraded if it has inconsistent data. MD
+tries to resync the array to bring it back to normal state. But before the
+resync completes, any system crash will expose the chance of real data
+corruption in the RAID array. This problem is called 'write hole'.
+
+The write-through cache will cache all data on cache disk first. After the data
+is safe on the cache disk, the data will be flushed onto RAID disks. The
+two-step write will guarantee MD can recover correct data after unclean
+shutdown even the array is degraded. Thus the cache can close the 'write hole'.
+
+In write-through mode, MD reports IO completion to upper layer (usually
+filesystems) after the data is safe on RAID disks, so cache disk failure
+doesn't cause data loss. Of course cache disk failure means the array is
+exposed to 'write hole' again.
+
+In write-through mode, the cache disk isn't required to be big. Several
+hundreds megabytes are enough.
+
+--------------------------------------
+write-back mode:
+
+write-back mode fixes the 'write hole' issue too, since all write data is
+cached on cache disk. But the main goal of 'write-back' cache is to speed up
+write. If a write crosses all RAID disks of a stripe, we call it full-stripe
+write. For non-full-stripe writes, MD must read old data before the new parity
+can be calculated. These synchronous reads hurt write throughput. Some writes
+which are sequential but not dispatched in the same time will suffer from this
+overhead too. Write-back cache will aggregate the data and flush the data to
+RAID disks only after the data becomes a full stripe write. This will
+completely avoid the overhead, so it's very helpful for some workloads. A
+typical workload which does sequential write followed by fsync is an example.
+
+In write-back mode, MD reports IO completion to upper layer (usually
+filesystems) right after the data hits cache disk. The data is flushed to raid
+disks later after specific conditions met. So cache disk failure will cause
+data loss.
+
+In write-back mode, MD also caches data in memory. The memory cache includes
+the same data stored on cache disk, so a power loss doesn't cause data loss.
+The memory cache size has performance impact for the array. It's recommended
+the size is big. A user can configure the size by:
+
+echo "2048" > /sys/block/md0/md/stripe_cache_size
+
+Too small cache disk will make the write aggregation less efficient in this
+mode depending on the workloads. It's recommended to use a cache disk with at
+least several gigabytes size in write-back mode.
+
+--------------------------------------
+The implementation:
+
+The write-through and write-back cache use the same disk format. The cache disk
+is organized as a simple write log. The log consists of 'meta data' and 'data'
+pairs. The meta data describes the data. It also includes checksum and sequence
+ID for recovery identification. Data can be IO data and parity data. Data is
+checksumed too. The checksum is stored in the meta data ahead of the data. The
+checksum is an optimization because MD can write meta and data freely without
+worry about the order. MD superblock has a field pointed to the valid meta data
+of log head.
+
+The log implementation is pretty straightforward. The difficult part is the
+order in which MD writes data to cache disk and RAID disks. Specifically, in
+write-through mode, MD calculates parity for IO data, writes both IO data and
+parity to the log, writes the data and parity to RAID disks after the data and
+parity is settled down in log and finally the IO is finished. Read just reads
+from raid disks as usual.
+
+In write-back mode, MD writes IO data to the log and reports IO completion. The
+data is also fully cached in memory at that time, which means read must query
+memory cache. If some conditions are met, MD will flush the data to RAID disks.
+MD will calculate parity for the data and write parity into the log. After this
+is finished, MD will write both data and parity into RAID disks, then MD can
+release the memory cache. The flush conditions could be stripe becomes a full
+stripe write, free cache disk space is low or free in-kernel memory cache space
+is low.
+
+After an unclean shutdown, MD does recovery. MD reads all meta data and data
+from the log. The sequence ID and checksum will help us detect corrupted meta
+data and data. If MD finds a stripe with data and valid parities (1 parity for
+raid4/5 and 2 for raid6), MD will write the data and parities to RAID disks. If
+parities are incompleted, they are discarded. If part of data is corrupted,
+they are discarded too. MD then loads valid data and writes them to RAID disks
+in normal way.

block/bio.c

@@ -625,21 +625,20 @@ struct bio *bio_clone_fast(struct bio *bio, gfp_t gfp_mask, struct bio_set *bs)
 }
 EXPORT_SYMBOL(bio_clone_fast);
 
-/**
- * 	bio_clone_bioset - clone a bio
- * 	@bio_src: bio to clone
- *	@gfp_mask: allocation priority
- *	@bs: bio_set to allocate from
- *
- *	Clone bio. Caller will own the returned bio, but not the actual data it
- *	points to. Reference count of returned bio will be one.
- */
-struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
-			     struct bio_set *bs)
+static struct bio *__bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
+				      struct bio_set *bs, int offset,
+				      int size)
 {
 	struct bvec_iter iter;
 	struct bio_vec bv;
 	struct bio *bio;
+	struct bvec_iter iter_src = bio_src->bi_iter;
+
+	/* for supporting partial clone */
+	if (offset || size != bio_src->bi_iter.bi_size) {
+		bio_advance_iter(bio_src, &iter_src, offset);
+		iter_src.bi_size = size;
+	}
 
 	/*
 	 * Pre immutable biovecs, __bio_clone() used to just do a memcpy from
@@ -663,7 +662,8 @@ struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
 	 *    __bio_clone_fast() anyways.
 	 */
 
-	bio = bio_alloc_bioset(gfp_mask, bio_segments(bio_src), bs);
+	bio = bio_alloc_bioset(gfp_mask, __bio_segments(bio_src,
+			       &iter_src), bs);
 	if (!bio)
 		return NULL;
 	bio->bi_bdev		= bio_src->bi_bdev;
@@ -680,7 +680,7 @@ struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
 		bio->bi_io_vec[bio->bi_vcnt++] = bio_src->bi_io_vec[0];
 		break;
 	default:
-		bio_for_each_segment(bv, bio_src, iter)
+		__bio_for_each_segment(bv, bio_src, iter, iter_src)
 			bio->bi_io_vec[bio->bi_vcnt++] = bv;
 		break;
 	}
@@ -699,8 +699,43 @@ struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
 
 	return bio;
 }
+
+/**
+ * 	bio_clone_bioset - clone a bio
+ * 	@bio_src: bio to clone
+ *	@gfp_mask: allocation priority
+ *	@bs: bio_set to allocate from
+ *
+ *	Clone bio. Caller will own the returned bio, but not the actual data it
+ *	points to. Reference count of returned bio will be one.
+ */
+struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
+			     struct bio_set *bs)
+{
+	return __bio_clone_bioset(bio_src, gfp_mask, bs, 0,
+				  bio_src->bi_iter.bi_size);
+}
 EXPORT_SYMBOL(bio_clone_bioset);
 
+/**
+ * 	bio_clone_bioset_partial - clone a partial bio
+ * 	@bio_src: bio to clone
+ *	@gfp_mask: allocation priority
+ *	@bs: bio_set to allocate from
+ *	@offset: cloned starting from the offset
+ *	@size: size for the cloned bio
+ *
+ *	Clone bio. Caller will own the returned bio, but not the actual data it
+ *	points to. Reference count of returned bio will be one.
+ */
+struct bio *bio_clone_bioset_partial(struct bio *bio_src, gfp_t gfp_mask,
+				     struct bio_set *bs, int offset,
+				     int size)
+{
+	return __bio_clone_bioset(bio_src, gfp_mask, bs, offset, size);
+}
+EXPORT_SYMBOL(bio_clone_bioset_partial);
+
 /**
  *	bio_add_pc_page	-	attempt to add page to bio
  *	@q: the target queue

drivers/md/faulty.c

@@ -214,7 +214,7 @@ static void faulty_make_request(struct mddev *mddev, struct bio *bio)
 		}
 	}
 	if (failit) {
-		struct bio *b = bio_clone_mddev(bio, GFP_NOIO, mddev);
+		struct bio *b = bio_clone_fast(bio, GFP_NOIO, mddev->bio_set);
 
 		b->bi_bdev = conf->rdev->bdev;
 		b->bi_private = bio;

drivers/md/linear.c

@@ -53,18 +53,26 @@ static inline struct dev_info *which_dev(struct mddev *mddev, sector_t sector)
 	return conf->disks + lo;
 }
 
+/*
+ * In linear_congested() conf->raid_disks is used as a copy of
+ * mddev->raid_disks to iterate conf->disks[], because conf->raid_disks
+ * and conf->disks[] are created in linear_conf(), they are always
+ * consitent with each other, but mddev->raid_disks does not.
+ */
 static int linear_congested(struct mddev *mddev, int bits)
 {
 	struct linear_conf *conf;
 	int i, ret = 0;
 
-	conf = mddev->private;
+	rcu_read_lock();
+	conf = rcu_dereference(mddev->private);
 
-	for (i = 0; i < mddev->raid_disks && !ret ; i++) {
+	for (i = 0; i < conf->raid_disks && !ret ; i++) {
 		struct request_queue *q = bdev_get_queue(conf->disks[i].rdev->bdev);
 		ret |= bdi_congested(q->backing_dev_info, bits);
 	}
 
+	rcu_read_unlock();
 	return ret;
 }
 
@@ -144,6 +152,19 @@ static struct linear_conf *linear_conf(struct mddev *mddev, int raid_disks)
 			conf->disks[i-1].end_sector +
 			conf->disks[i].rdev->sectors;
 
+	/*
+	 * conf->raid_disks is copy of mddev->raid_disks. The reason to
+	 * keep a copy of mddev->raid_disks in struct linear_conf is,
+	 * mddev->raid_disks may not be consistent with pointers number of
+	 * conf->disks[] when it is updated in linear_add() and used to
+	 * iterate old conf->disks[] earray in linear_congested().
+	 * Here conf->raid_disks is always consitent with number of
+	 * pointers in conf->disks[] array, and mddev->private is updated
+	 * with rcu_assign_pointer() in linear_addr(), such race can be
+	 * avoided.
+	 */
+	conf->raid_disks = raid_disks;
+
 	return conf;
 
 out:
@@ -196,15 +217,24 @@ static int linear_add(struct mddev *mddev, struct md_rdev *rdev)
 	if (!newconf)
 		return -ENOMEM;
 
+	/* newconf->raid_disks already keeps a copy of * the increased
+	 * value of mddev->raid_disks, WARN_ONCE() is just used to make
+	 * sure of this. It is possible that oldconf is still referenced
+	 * in linear_congested(), therefore kfree_rcu() is used to free
+	 * oldconf until no one uses it anymore.
+	 */
 	mddev_suspend(mddev);
-	oldconf = mddev->private;
+	oldconf = rcu_dereference_protected(mddev->private,
+			lockdep_is_held(&mddev->reconfig_mutex));
 	mddev->raid_disks++;
-	mddev->private = newconf;
+	WARN_ONCE(mddev->raid_disks != newconf->raid_disks,
+		"copied raid_disks doesn't match mddev->raid_disks");
+	rcu_assign_pointer(mddev->private, newconf);
 	md_set_array_sectors(mddev, linear_size(mddev, 0, 0));
 	set_capacity(mddev->gendisk, mddev->array_sectors);
 	mddev_resume(mddev);
 	revalidate_disk(mddev->gendisk);
-	kfree(oldconf);
+	kfree_rcu(oldconf, rcu);
 	return 0;
 }
 
@@ -262,6 +292,7 @@ static void linear_make_request(struct mddev *mddev, struct bio *bio)
 				trace_block_bio_remap(bdev_get_queue(split->bi_bdev),
 						      split, disk_devt(mddev->gendisk),
 						      bio_sector);
+			mddev_check_writesame(mddev, split);
 			generic_make_request(split);
 		}
 	} while (split != bio);

drivers/md/linear.h

@@ -10,6 +10,7 @@ struct linear_conf
 {
 	struct rcu_head		rcu;
 	sector_t		array_sectors;
+	int			raid_disks; /* a copy of mddev->raid_disks */
 	struct dev_info		disks[0];
 };
 #endif

drivers/md/md.c

@@ -190,16 +190,6 @@ struct bio *bio_alloc_mddev(gfp_t gfp_mask, int nr_iovecs,
 }
 EXPORT_SYMBOL_GPL(bio_alloc_mddev);
 
-struct bio *bio_clone_mddev(struct bio *bio, gfp_t gfp_mask,
-			    struct mddev *mddev)
-{
-	if (!mddev || !mddev->bio_set)
-		return bio_clone(bio, gfp_mask);
-
-	return bio_clone_bioset(bio, gfp_mask, mddev->bio_set);
-}
-EXPORT_SYMBOL_GPL(bio_clone_mddev);
-
 /*
  * We have a system wide 'event count' that is incremented
  * on any 'interesting' event, and readers of /proc/mdstat
@@ -5228,8 +5218,11 @@ int md_run(struct mddev *mddev)
 		sysfs_notify_dirent_safe(rdev->sysfs_state);
 	}
 
-	if (mddev->bio_set == NULL)
+	if (mddev->bio_set == NULL) {
 		mddev->bio_set = bioset_create(BIO_POOL_SIZE, 0);
+		if (!mddev->bio_set)
+			return -ENOMEM;
+	}
 
 	spin_lock(&pers_lock);
 	pers = find_pers(mddev->level, mddev->clevel);
@@ -8980,7 +8973,14 @@ static __exit void md_exit(void)
 
 	for_each_mddev(mddev, tmp) {
 		export_array(mddev);
+		mddev->ctime = 0;
 		mddev->hold_active = 0;
+		/*
+		 * for_each_mddev() will call mddev_put() at the end of each
+		 * iteration.  As the mddev is now fully clear, this will
+		 * schedule the mddev for destruction by a workqueue, and the
+		 * destroy_workqueue() below will wait for that to complete.
+		 */
 	}
 	destroy_workqueue(md_misc_wq);
 	destroy_workqueue(md_wq);

drivers/md/md.h

@@ -673,8 +673,6 @@ extern void md_rdev_clear(struct md_rdev *rdev);
 
 extern void mddev_suspend(struct mddev *mddev);
 extern void mddev_resume(struct mddev *mddev);
-extern struct bio *bio_clone_mddev(struct bio *bio, gfp_t gfp_mask,
-				   struct mddev *mddev);
 extern struct bio *bio_alloc_mddev(gfp_t gfp_mask, int nr_iovecs,
 				   struct mddev *mddev);
 
@@ -710,4 +708,11 @@ static inline void mddev_clear_unsupported_flags(struct mddev *mddev,
 {
 	mddev->flags &= ~unsupported_flags;
 }
+
+static inline void mddev_check_writesame(struct mddev *mddev, struct bio *bio)
+{
+	if (bio_op(bio) == REQ_OP_WRITE_SAME &&
+	    !bdev_get_queue(bio->bi_bdev)->limits.max_write_same_sectors)
+		mddev->queue->limits.max_write_same_sectors = 0;
+}
 #endif /* _MD_MD_H */

drivers/md/multipath.c

@@ -138,6 +138,7 @@ static void multipath_make_request(struct mddev *mddev, struct bio * bio)
 	mp_bh->bio.bi_opf |= REQ_FAILFAST_TRANSPORT;
 	mp_bh->bio.bi_end_io = multipath_end_request;
 	mp_bh->bio.bi_private = mp_bh;
+	mddev_check_writesame(mddev, &mp_bh->bio);
 	generic_make_request(&mp_bh->bio);
 	return;
 }

drivers/md/raid0.c

@@ -503,6 +503,7 @@ static void raid0_make_request(struct mddev *mddev, struct bio *bio)
 				trace_block_bio_remap(bdev_get_queue(split->bi_bdev),
 						      split, disk_devt(mddev->gendisk),
 						      bio_sector);
+			mddev_check_writesame(mddev, split);
 			generic_make_request(split);
 		}
 	} while (split != bio);

drivers/md/raid1.c

@@ -71,9 +71,8 @@
  */
 static int max_queued_requests = 1024;
 
-static void allow_barrier(struct r1conf *conf, sector_t start_next_window,
-			  sector_t bi_sector);
-static void lower_barrier(struct r1conf *conf);
+static void allow_barrier(struct r1conf *conf, sector_t sector_nr);
+static void lower_barrier(struct r1conf *conf, sector_t sector_nr);
 
 #define raid1_log(md, fmt, args...)				\
 	do { if ((md)->queue) blk_add_trace_msg((md)->queue, "raid1 " fmt, ##args); } while (0)
@@ -100,7 +99,6 @@ static void r1bio_pool_free(void *r1_bio, void *data)
 #define RESYNC_WINDOW_SECTORS (RESYNC_WINDOW >> 9)
 #define CLUSTER_RESYNC_WINDOW (16 * RESYNC_WINDOW)
 #define CLUSTER_RESYNC_WINDOW_SECTORS (CLUSTER_RESYNC_WINDOW >> 9)
-#define NEXT_NORMALIO_DISTANCE (3 * RESYNC_WINDOW_SECTORS)
 
 static void * r1buf_pool_alloc(gfp_t gfp_flags, void *data)
 {
@@ -205,6 +203,7 @@ static void free_r1bio(struct r1bio *r1_bio)
 static void put_buf(struct r1bio *r1_bio)
 {
 	struct r1conf *conf = r1_bio->mddev->private;
+	sector_t sect = r1_bio->sector;
 	int i;
 
 	for (i = 0; i < conf->raid_disks * 2; i++) {
@@ -215,7 +214,7 @@ static void put_buf(struct r1bio *r1_bio)
 
 	mempool_free(r1_bio, conf->r1buf_pool);
 
-	lower_barrier(conf);
+	lower_barrier(conf, sect);
 }
 
 static void reschedule_retry(struct r1bio *r1_bio)
@@ -223,10 +222,12 @@ static void reschedule_retry(struct r1bio *r1_bio)
 	unsigned long flags;
 	struct mddev *mddev = r1_bio->mddev;
 	struct r1conf *conf = mddev->private;
+	int idx;
 
+	idx = sector_to_idx(r1_bio->sector);
 	spin_lock_irqsave(&conf->device_lock, flags);
 	list_add(&r1_bio->retry_list, &conf->retry_list);
-	conf->nr_queued ++;
+	atomic_inc(&conf->nr_queued[idx]);
 	spin_unlock_irqrestore(&conf->device_lock, flags);
 
 	wake_up(&conf->wait_barrier);
@@ -243,7 +244,6 @@ static void call_bio_endio(struct r1bio *r1_bio)
 	struct bio *bio = r1_bio->master_bio;
 	int done;
 	struct r1conf *conf = r1_bio->mddev->private;
-	sector_t start_next_window = r1_bio->start_next_window;
 	sector_t bi_sector = bio->bi_iter.bi_sector;
 
 	if (bio->bi_phys_segments) {
@@ -269,7 +269,7 @@ static void call_bio_endio(struct r1bio *r1_bio)
 		 * Wake up any possible resync thread that waits for the device
 		 * to go idle.
 		 */
-		allow_barrier(conf, start_next_window, bi_sector);
+		allow_barrier(conf, bi_sector);
 	}
 }
 
@@ -517,6 +517,25 @@ static void raid1_end_write_request(struct bio *bio)
 		bio_put(to_put);
 }
 
+static sector_t align_to_barrier_unit_end(sector_t start_sector,
+					  sector_t sectors)
+{
+	sector_t len;
+
+	WARN_ON(sectors == 0);
+	/*
+	 * len is the number of sectors from start_sector to end of the
+	 * barrier unit which start_sector belongs to.
+	 */
+	len = round_up(start_sector + 1, BARRIER_UNIT_SECTOR_SIZE) -
+	      start_sector;
+
+	if (len > sectors)
+		len = sectors;
+
+	return len;
+}
+
 /*
  * This routine returns the disk from which the requested read should
  * be done. There is a per-array 'next expected sequential IO' sector
@@ -813,166 +832,226 @@ static void flush_pending_writes(struct r1conf *conf)
  */
 static void raise_barrier(struct r1conf *conf, sector_t sector_nr)
 {
+	int idx = sector_to_idx(sector_nr);
+
 	spin_lock_irq(&conf->resync_lock);
 
 	/* Wait until no block IO is waiting */
-	wait_event_lock_irq(conf->wait_barrier, !conf->nr_waiting,
+	wait_event_lock_irq(conf->wait_barrier,
+			    !atomic_read(&conf->nr_waiting[idx]),
 			    conf->resync_lock);
 
 	/* block any new IO from starting */
-	conf->barrier++;
-	conf->next_resync = sector_nr;
+	atomic_inc(&conf->barrier[idx]);
+	/*
+	 * In raise_barrier() we firstly increase conf->barrier[idx] then
+	 * check conf->nr_pending[idx]. In _wait_barrier() we firstly
+	 * increase conf->nr_pending[idx] then check conf->barrier[idx].
+	 * A memory barrier here to make sure conf->nr_pending[idx] won't
+	 * be fetched before conf->barrier[idx] is increased. Otherwise
+	 * there will be a race between raise_barrier() and _wait_barrier().
+	 */
+	smp_mb__after_atomic();
 
 	/* For these conditions we must wait:
 	 * A: while the array is in frozen state
-	 * B: while barrier >= RESYNC_DEPTH, meaning resync reach
-	 *    the max count which allowed.
-	 * C: next_resync + RESYNC_SECTORS > start_next_window, meaning
-	 *    next resync will reach to the window which normal bios are
-	 *    handling.
-	 * D: while there are any active requests in the current window.
+	 * B: while conf->nr_pending[idx] is not 0, meaning regular I/O
+	 *    existing in corresponding I/O barrier bucket.
+	 * C: while conf->barrier[idx] >= RESYNC_DEPTH, meaning reaches
+	 *    max resync count which allowed on current I/O barrier bucket.
 	 */
 	wait_event_lock_irq(conf->wait_barrier,
 			    !conf->array_frozen &&
-			    conf->barrier < RESYNC_DEPTH &&
-			    conf->current_window_requests == 0 &&
-			    (conf->start_next_window >=
-			     conf->next_resync + RESYNC_SECTORS),
+			     !atomic_read(&conf->nr_pending[idx]) &&
+			     atomic_read(&conf->barrier[idx]) < RESYNC_DEPTH,
 			    conf->resync_lock);
 
-	conf->nr_pending++;
+	atomic_inc(&conf->nr_pending[idx]);
 	spin_unlock_irq(&conf->resync_lock);
 }
 
-static void lower_barrier(struct r1conf *conf)
+static void lower_barrier(struct r1conf *conf, sector_t sector_nr)
 {
-	unsigned long flags;
-	BUG_ON(conf->barrier <= 0);
-	spin_lock_irqsave(&conf->resync_lock, flags);
-	conf->barrier--;
-	conf->nr_pending--;
-	spin_unlock_irqrestore(&conf->resync_lock, flags);
+	int idx = sector_to_idx(sector_nr);
+
+	BUG_ON(atomic_read(&conf->barrier[idx]) <= 0);
+
+	atomic_dec(&conf->barrier[idx]);
+	atomic_dec(&conf->nr_pending[idx]);
 	wake_up(&conf->wait_barrier);
 }
 
-static bool need_to_wait_for_sync(struct r1conf *conf, struct bio *bio)
+static void _wait_barrier(struct r1conf *conf, int idx)
 {
-	bool wait = false;
+	/*
+	 * We need to increase conf->nr_pending[idx] very early here,
+	 * then raise_barrier() can be blocked when it waits for
+	 * conf->nr_pending[idx] to be 0. Then we can avoid holding
+	 * conf->resync_lock when there is no barrier raised in same
+	 * barrier unit bucket. Also if the array is frozen, I/O
+	 * should be blocked until array is unfrozen.
+	 */
+	atomic_inc(&conf->nr_pending[idx]);
+	/*
+	 * In _wait_barrier() we firstly increase conf->nr_pending[idx], then
+	 * check conf->barrier[idx]. In raise_barrier() we firstly increase
+	 * conf->barrier[idx], then check conf->nr_pending[idx]. A memory
+	 * barrier is necessary here to make sure conf->barrier[idx] won't be
+	 * fetched before conf->nr_pending[idx] is increased. Otherwise there
+	 * will be a race between _wait_barrier() and raise_barrier().
+	 */
+	smp_mb__after_atomic();
 
-	if (conf->array_frozen || !bio)
-		wait = true;
-	else if (conf->barrier && bio_data_dir(bio) == WRITE) {
-		if ((conf->mddev->curr_resync_completed
-		     >= bio_end_sector(bio)) ||
-		    (conf->start_next_window + NEXT_NORMALIO_DISTANCE
-		     <= bio->bi_iter.bi_sector))
-			wait = false;
-		else
-			wait = true;
-	}
+	/*
+	 * Don't worry about checking two atomic_t variables at same time
+	 * here. If during we check conf->barrier[idx], the array is
+	 * frozen (conf->array_frozen is 1), and chonf->barrier[idx] is
+	 * 0, it is safe to return and make the I/O continue. Because the
+	 * array is frozen, all I/O returned here will eventually complete
+	 * or be queued, no race will happen. See code comment in
+	 * frozen_array().
+	 */
+	if (!READ_ONCE(conf->array_frozen) &&
+	    !atomic_read(&conf->barrier[idx]))
+		return;
 
-	return wait;
+	/*
+	 * After holding conf->resync_lock, conf->nr_pending[idx]
+	 * should be decreased before waiting for barrier to drop.
+	 * Otherwise, we may encounter a race condition because
+	 * raise_barrer() might be waiting for conf->nr_pending[idx]
+	 * to be 0 at same time.
+	 */
+	spin_lock_irq(&conf->resync_lock);
+	atomic_inc(&conf->nr_waiting[idx]);
+	atomic_dec(&conf->nr_pending[idx]);
+	/*
+	 * In case freeze_array() is waiting for
+	 * get_unqueued_pending() == extra
+	 */
+	wake_up(&conf->wait_barrier);
+	/* Wait for the barrier in same barrier unit bucket to drop. */
+	wait_event_lock_irq(conf->wait_barrier,
+			    !conf->array_frozen &&
+			     !atomic_read(&conf->barrier[idx]),
+			    conf->resync_lock);
+	atomic_inc(&conf->nr_pending[idx]);
+	atomic_dec(&conf->nr_waiting[idx]);
+	spin_unlock_irq(&conf->resync_lock);
 }
 
-static sector_t wait_barrier(struct r1conf *conf, struct bio *bio)
+static void wait_read_barrier(struct r1conf *conf, sector_t sector_nr)
 {
-	sector_t sector = 0;
+	int idx = sector_to_idx(sector_nr);
+
+	/*
+	 * Very similar to _wait_barrier(). The difference is, for read
+	 * I/O we don't need wait for sync I/O, but if the whole array
+	 * is frozen, the read I/O still has to wait until the array is
+	 * unfrozen. Since there is no ordering requirement with
+	 * conf->barrier[idx] here, memory barrier is unnecessary as well.
+	 */
+	atomic_inc(&conf->nr_pending[idx]);
+
+	if (!READ_ONCE(conf->array_frozen))
+		return;
 
 	spin_lock_irq(&conf->resync_lock);
-	if (need_to_wait_for_sync(conf, bio)) {
-		conf->nr_waiting++;
-		/* Wait for the barrier to drop.
-		 * However if there are already pending
-		 * requests (preventing the barrier from
-		 * rising completely), and the
-		 * per-process bio queue isn't empty,
-		 * then don't wait, as we need to empty
-		 * that queue to allow conf->start_next_window
-		 * to increase.
-		 */
-		raid1_log(conf->mddev, "wait barrier");
+	atomic_inc(&conf->nr_waiting[idx]);
+	atomic_dec(&conf->nr_pending[idx]);
+	/*
+	 * In case freeze_array() is waiting for
+	 * get_unqueued_pending() == extra
+	 */
+	wake_up(&conf->wait_barrier);
+	/* Wait for array to be unfrozen */
 	wait_event_lock_irq(conf->wait_barrier,
-				    !conf->array_frozen &&
-				    (!conf->barrier ||
-				     ((conf->start_next_window <
-				       conf->next_resync + RESYNC_SECTORS) &&
-				      current->bio_list &&
-				      !bio_list_empty(current->bio_list))),
+			    !conf->array_frozen,
 			    conf->resync_lock);
-		conf->nr_waiting--;
-	}
-
-	if (bio && bio_data_dir(bio) == WRITE) {
-		if (bio->bi_iter.bi_sector >= conf->next_resync) {
-			if (conf->start_next_window == MaxSector)
-				conf->start_next_window =
-					conf->next_resync +
-					NEXT_NORMALIO_DISTANCE;
+	atomic_inc(&conf->nr_pending[idx]);
+	atomic_dec(&conf->nr_waiting[idx]);
+	spin_unlock_irq(&conf->resync_lock);
+}
 
-			if ((conf->start_next_window + NEXT_NORMALIO_DISTANCE)
-			    <= bio->bi_iter.bi_sector)
-				conf->next_window_requests++;
-			else
-				conf->current_window_requests++;
-			sector = conf->start_next_window;
-		}
-	}
+static void wait_barrier(struct r1conf *conf, sector_t sector_nr)
+{
+	int idx = sector_to_idx(sector_nr);
 
-	conf->nr_pending++;
-	spin_unlock_irq(&conf->resync_lock);
-	return sector;
+	_wait_barrier(conf, idx);
 }
 
-static void allow_barrier(struct r1conf *conf, sector_t start_next_window,
-			  sector_t bi_sector)
+static void wait_all_barriers(struct r1conf *conf)
 {
-	unsigned long flags;
+	int idx;
 
-	spin_lock_irqsave(&conf->resync_lock, flags);
-	conf->nr_pending--;
-	if (start_next_window) {
-		if (start_next_window == conf->start_next_window) {
-			if (conf->start_next_window + NEXT_NORMALIO_DISTANCE
-			    <= bi_sector)
-				conf->next_window_requests--;
-			else
-				conf->current_window_requests--;
-		} else
-			conf->current_window_requests--;
-
-		if (!conf->current_window_requests) {
-			if (conf->next_window_requests) {
-				conf->current_window_requests =
-					conf->next_window_requests;
-				conf->next_window_requests = 0;
-				conf->start_next_window +=
-					NEXT_NORMALIO_DISTANCE;
-			} else
-				conf->start_next_window = MaxSector;
-		}
-	}
-	spin_unlock_irqrestore(&conf->resync_lock, flags);
+	for (idx = 0; idx < BARRIER_BUCKETS_NR; idx++)
+		_wait_barrier(conf, idx);
+}
+
+static void _allow_barrier(struct r1conf *conf, int idx)
+{
+	atomic_dec(&conf->nr_pending[idx]);
 	wake_up(&conf->wait_barrier);
 }
 
+static void allow_barrier(struct r1conf *conf, sector_t sector_nr)
+{
+	int idx = sector_to_idx(sector_nr);
+
+	_allow_barrier(conf, idx);
+}
+
+static void allow_all_barriers(struct r1conf *conf)
+{
+	int idx;
+
+	for (idx = 0; idx < BARRIER_BUCKETS_NR; idx++)
+		_allow_barrier(conf, idx);
+}
+
+/* conf->resync_lock should be held */
+static int get_unqueued_pending(struct r1conf *conf)
+{
+	int idx, ret;
+
+	for (ret = 0, idx = 0; idx < BARRIER_BUCKETS_NR; idx++)
+		ret += atomic_read(&conf->nr_pending[idx]) -
+			atomic_read(&conf->nr_queued[idx]);
+
+	return ret;
+}
+
 static void freeze_array(struct r1conf *conf, int extra)
 {
-	/* stop syncio and normal IO and wait for everything to
+	/* Stop sync I/O and normal I/O and wait for everything to
 	 * go quite.
-	 * We wait until nr_pending match nr_queued+extra
-	 * This is called in the context of one normal IO request
-	 * that has failed. Thus any sync request that might be pending
-	 * will be blocked by nr_pending, and we need to wait for
-	 * pending IO requests to complete or be queued for re-try.
-	 * Thus the number queued (nr_queued) plus this request (extra)
-	 * must match the number of pending IOs (nr_pending) before
-	 * we continue.
+	 * This is called in two situations:
+	 * 1) management command handlers (reshape, remove disk, quiesce).
+	 * 2) one normal I/O request failed.
+
+	 * After array_frozen is set to 1, new sync IO will be blocked at
+	 * raise_barrier(), and new normal I/O will blocked at _wait_barrier()
+	 * or wait_read_barrier(). The flying I/Os will either complete or be
+	 * queued. When everything goes quite, there are only queued I/Os left.
+
+	 * Every flying I/O contributes to a conf->nr_pending[idx], idx is the
+	 * barrier bucket index which this I/O request hits. When all sync and
+	 * normal I/O are queued, sum of all conf->nr_pending[] will match sum
+	 * of all conf->nr_queued[]. But normal I/O failure is an exception,
+	 * in handle_read_error(), we may call freeze_array() before trying to
+	 * fix the read error. In this case, the error read I/O is not queued,
+	 * so get_unqueued_pending() == 1.
+	 *
+	 * Therefore before this function returns, we need to wait until
+	 * get_unqueued_pendings(conf) gets equal to extra. For
+	 * normal I/O context, extra is 1, in rested situations extra is 0.
 	 */
 	spin_lock_irq(&conf->resync_lock);
 	conf->array_frozen = 1;
 	raid1_log(conf->mddev, "wait freeze");
-	wait_event_lock_irq_cmd(conf->wait_barrier,
-				conf->nr_pending == conf->nr_queued+extra,
+	wait_event_lock_irq_cmd(
+		conf->wait_barrier,
+		get_unqueued_pending(conf) == extra,
 		conf->resync_lock,
 		flush_pending_writes(conf));
 	spin_unlock_irq(&conf->resync_lock);
@@ -982,8 +1061,8 @@ static void unfreeze_array(struct r1conf *conf)
 	/* reverse the effect of the freeze */
 	spin_lock_irq(&conf->resync_lock);
 	conf->array_frozen = 0;
-	wake_up(&conf->wait_barrier);
 	spin_unlock_irq(&conf->resync_lock);
+	wake_up(&conf->wait_barrier);
 }
 
 /* duplicate the data pages for behind I/O
@@ -1070,11 +1149,28 @@ static void raid1_unplug(struct blk_plug_cb *cb, bool from_schedule)
 	kfree(plug);
 }
 
-static void raid1_read_request(struct mddev *mddev, struct bio *bio,
-				 struct r1bio *r1_bio)
+static inline struct r1bio *
+alloc_r1bio(struct mddev *mddev, struct bio *bio, sector_t sectors_handled)
+{
+	struct r1conf *conf = mddev->private;
+	struct r1bio *r1_bio;
+
+	r1_bio = mempool_alloc(conf->r1bio_pool, GFP_NOIO);
+
+	r1_bio->master_bio = bio;
+	r1_bio->sectors = bio_sectors(bio) - sectors_handled;
+	r1_bio->state = 0;
+	r1_bio->mddev = mddev;
+	r1_bio->sector = bio->bi_iter.bi_sector + sectors_handled;
+
+	return r1_bio;
+}
+
+static void raid1_read_request(struct mddev *mddev, struct bio *bio)
 {
 	struct r1conf *conf = mddev->private;
 	struct raid1_info *mirror;
+	struct r1bio *r1_bio;
 	struct bio *read_bio;
 	struct bitmap *bitmap = mddev->bitmap;
 	const int op = bio_op(bio);
@@ -1083,8 +1179,29 @@ static void raid1_read_request(struct mddev *mddev, struct bio *bio,
 	int max_sectors;
 	int rdisk;
 
-	wait_barrier(conf, bio);
+	/*
+	 * Still need barrier for READ in case that whole
+	 * array is frozen.
+	 */
+	wait_read_barrier(conf, bio->bi_iter.bi_sector);
+
+	r1_bio = alloc_r1bio(mddev, bio, 0);
+
+	/*
+	 * We might need to issue multiple reads to different
+	 * devices if there are bad blocks around, so we keep
+	 * track of the number of reads in bio->bi_phys_segments.
+	 * If this is 0, there is only one r1_bio and no locking
+	 * will be needed when requests complete.  If it is
+	 * non-zero, then it is the number of not-completed requests.
+	 */
+	bio->bi_phys_segments = 0;
+	bio_clear_flag(bio, BIO_SEG_VALID);
 
+	/*
+	 * make_request() can abort the operation when read-ahead is being
+	 * used and no empty request is available.
+	 */
 read_again:
 	rdisk = read_balance(conf, r1_bio, &max_sectors);
 
@@ -1106,9 +1223,8 @@ static void raid1_read_request(struct mddev *mddev, struct bio *bio,
 			   atomic_read(&bitmap->behind_writes) == 0);
 	}
 	r1_bio->read_disk = rdisk;
-	r1_bio->start_next_window = 0;
 
-	read_bio = bio_clone_mddev(bio, GFP_NOIO, mddev);
+	read_bio = bio_clone_fast(bio, GFP_NOIO, mddev->bio_set);
 	bio_trim(read_bio, r1_bio->sector - bio->bi_iter.bi_sector,
 		 max_sectors);
 
@@ -1151,22 +1267,16 @@ static void raid1_read_request(struct mddev *mddev, struct bio *bio,
 		 */
 		reschedule_retry(r1_bio);
 
-		r1_bio = mempool_alloc(conf->r1bio_pool, GFP_NOIO);
-
-		r1_bio->master_bio = bio;
-		r1_bio->sectors = bio_sectors(bio) - sectors_handled;
-		r1_bio->state = 0;
-		r1_bio->mddev = mddev;
-		r1_bio->sector = bio->bi_iter.bi_sector + sectors_handled;
+		r1_bio = alloc_r1bio(mddev, bio, sectors_handled);
 		goto read_again;
 	} else
 		generic_make_request(read_bio);
 }
 
-static void raid1_write_request(struct mddev *mddev, struct bio *bio,
-				struct r1bio *r1_bio)
+static void raid1_write_request(struct mddev *mddev, struct bio *bio)
 {
 	struct r1conf *conf = mddev->private;
+	struct r1bio *r1_bio;
 	int i, disks;
 	struct bitmap *bitmap = mddev->bitmap;
 	unsigned long flags;
@@ -1176,7 +1286,6 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
 	int first_clone;
 	int sectors_handled;
 	int max_sectors;
-	sector_t start_next_window;
 
 	/*
 	 * Register the new request and wait if the reconstruction
@@ -1212,7 +1321,19 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
 		}
 		finish_wait(&conf->wait_barrier, &w);
 	}
-	start_next_window = wait_barrier(conf, bio);
+	wait_barrier(conf, bio->bi_iter.bi_sector);
+
+	r1_bio = alloc_r1bio(mddev, bio, 0);
+
+	/* We might need to issue multiple writes to different
+	 * devices if there are bad blocks around, so we keep
+	 * track of the number of writes in bio->bi_phys_segments.
+	 * If this is 0, there is only one r1_bio and no locking
+	 * will be needed when requests complete.  If it is
+	 * non-zero, then it is the number of not-completed requests.
+	 */
+	bio->bi_phys_segments = 0;
+	bio_clear_flag(bio, BIO_SEG_VALID);
 
 	if (conf->pending_count >= max_queued_requests) {
 		md_wakeup_thread(mddev->thread);
@@ -1233,7 +1354,6 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
 
 	disks = conf->raid_disks * 2;
  retry_write:
-	r1_bio->start_next_window = start_next_window;
 	blocked_rdev = NULL;
 	rcu_read_lock();
 	max_sectors = r1_bio->sectors;
@@ -1300,25 +1420,15 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
 	if (unlikely(blocked_rdev)) {
 		/* Wait for this device to become unblocked */
 		int j;
-		sector_t old = start_next_window;
 
 		for (j = 0; j < i; j++)
 			if (r1_bio->bios[j])
 				rdev_dec_pending(conf->mirrors[j].rdev, mddev);
 		r1_bio->state = 0;
-		allow_barrier(conf, start_next_window, bio->bi_iter.bi_sector);
+		allow_barrier(conf, bio->bi_iter.bi_sector);
 		raid1_log(mddev, "wait rdev %d blocked", blocked_rdev->raid_disk);
 		md_wait_for_blocked_rdev(blocked_rdev, mddev);
-		start_next_window = wait_barrier(conf, bio);
-		/*
-		 * We must make sure the multi r1bios of bio have
-		 * the same value of bi_phys_segments
-		 */
-		if (bio->bi_phys_segments && old &&
-		    old != start_next_window)
-			/* Wait for the former r1bio(s) to complete */
-			wait_event(conf->wait_barrier,
-				   bio->bi_phys_segments == 1);
+		wait_barrier(conf, bio->bi_iter.bi_sector);
 		goto retry_write;
 	}
 
@@ -1341,13 +1451,12 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
 
 	first_clone = 1;
 	for (i = 0; i < disks; i++) {
-		struct bio *mbio;
+		struct bio *mbio = NULL;
+		sector_t offset;
 		if (!r1_bio->bios[i])
 			continue;
 
-		mbio = bio_clone_mddev(bio, GFP_NOIO, mddev);
-		bio_trim(mbio, r1_bio->sector - bio->bi_iter.bi_sector,
-			 max_sectors);
+		offset = r1_bio->sector - bio->bi_iter.bi_sector;
 
 		if (first_clone) {
 			/* do behind I/O ?
@@ -1357,8 +1466,13 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
 			if (bitmap &&
 			    (atomic_read(&bitmap->behind_writes)
 			     < mddev->bitmap_info.max_write_behind) &&
-			    !waitqueue_active(&bitmap->behind_wait))
+			    !waitqueue_active(&bitmap->behind_wait)) {
+				mbio = bio_clone_bioset_partial(bio, GFP_NOIO,
+								mddev->bio_set,
+								offset << 9,
+								max_sectors << 9);
 				alloc_behind_pages(mbio, r1_bio);
+			}
 
 			bitmap_startwrite(bitmap, r1_bio->sector,
 					  r1_bio->sectors,
@@ -1366,6 +1480,19 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
 						   &r1_bio->state));
 			first_clone = 0;
 		}
+
+		if (!mbio) {
+			if (r1_bio->behind_bvecs)
+				mbio = bio_clone_bioset_partial(bio, GFP_NOIO,
+								mddev->bio_set,
+								offset << 9,
+								max_sectors << 9);
+			else {
+				mbio = bio_clone_fast(bio, GFP_NOIO, mddev->bio_set);
+				bio_trim(mbio, offset, max_sectors);
+			}
+		}
+
 		if (r1_bio->behind_bvecs) {
 			struct bio_vec *bvec;
 			int j;
@@ -1385,8 +1512,7 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
 				   conf->mirrors[i].rdev->data_offset);
 		mbio->bi_bdev = conf->mirrors[i].rdev->bdev;
 		mbio->bi_end_io	= raid1_end_write_request;
-		mbio->bi_opf = bio_op(bio) |
-			(bio->bi_opf & (REQ_SYNC | REQ_PREFLUSH | REQ_FUA));
+		mbio->bi_opf = bio_op(bio) | (bio->bi_opf & (REQ_SYNC | REQ_FUA));
 		if (test_bit(FailFast, &conf->mirrors[i].rdev->flags) &&
 		    !test_bit(WriteMostly, &conf->mirrors[i].rdev->flags) &&
 		    conf->raid_disks - mddev->degraded > 1)
@@ -1427,12 +1553,7 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
 		/* We need another r1_bio.  It has already been counted
 		 * in bio->bi_phys_segments
 		 */
-		r1_bio = mempool_alloc(conf->r1bio_pool, GFP_NOIO);
-		r1_bio->master_bio = bio;
-		r1_bio->sectors = bio_sectors(bio) - sectors_handled;
-		r1_bio->state = 0;
-		r1_bio->mddev = mddev;
-		r1_bio->sector = bio->bi_iter.bi_sector + sectors_handled;
+		r1_bio = alloc_r1bio(mddev, bio, sectors_handled);
 		goto retry_write;
 	}
 
@@ -1444,36 +1565,30 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
 
 static void raid1_make_request(struct mddev *mddev, struct bio *bio)
 {
-	struct r1conf *conf = mddev->private;
-	struct r1bio *r1_bio;
-
-	/*
-	 * make_request() can abort the operation when read-ahead is being
-	 * used and no empty request is available.
-	 *
-	 */
-	r1_bio = mempool_alloc(conf->r1bio_pool, GFP_NOIO);
+	struct bio *split;
+	sector_t sectors;
 
-	r1_bio->master_bio = bio;
-	r1_bio->sectors = bio_sectors(bio);
-	r1_bio->state = 0;
-	r1_bio->mddev = mddev;
-	r1_bio->sector = bio->bi_iter.bi_sector;
+	if (unlikely(bio->bi_opf & REQ_PREFLUSH)) {
+		md_flush_request(mddev, bio);
+		return;
+	}
 
-	/*
-	 * We might need to issue multiple reads to different devices if there
-	 * are bad blocks around, so we keep track of the number of reads in
-	 * bio->bi_phys_segments.  If this is 0, there is only one r1_bio and
-	 * no locking will be needed when requests complete.  If it is
-	 * non-zero, then it is the number of not-completed requests.
-	 */
-	bio->bi_phys_segments = 0;
-	bio_clear_flag(bio, BIO_SEG_VALID);
+	/* if bio exceeds barrier unit boundary, split it */
+	do {
+		sectors = align_to_barrier_unit_end(
+				bio->bi_iter.bi_sector, bio_sectors(bio));
+		if (sectors < bio_sectors(bio)) {
+			split = bio_split(bio, sectors, GFP_NOIO, fs_bio_set);
+			bio_chain(split, bio);
+		} else {
+			split = bio;
+		}
 
-	if (bio_data_dir(bio) == READ)
-		raid1_read_request(mddev, bio, r1_bio);
+		if (bio_data_dir(split) == READ)
+			raid1_read_request(mddev, split);
 		else
-		raid1_write_request(mddev, bio, r1_bio);
+			raid1_write_request(mddev, split);
+	} while (split != bio);
 }
 
 static void raid1_status(struct seq_file *seq, struct mddev *mddev)
@@ -1564,19 +1679,11 @@ static void print_conf(struct r1conf *conf)
 
 static void close_sync(struct r1conf *conf)
 {
-	wait_barrier(conf, NULL);
-	allow_barrier(conf, 0, 0);
+	wait_all_barriers(conf);
+	allow_all_barriers(conf);
 
 	mempool_destroy(conf->r1buf_pool);
 	conf->r1buf_pool = NULL;
-
-	spin_lock_irq(&conf->resync_lock);
-	conf->next_resync = MaxSector - 2 * NEXT_NORMALIO_DISTANCE;
-	conf->start_next_window = MaxSector;
-	conf->current_window_requests +=
-		conf->next_window_requests;
-	conf->next_window_requests = 0;
-	spin_unlock_irq(&conf->resync_lock);
 }
 
 static int raid1_spare_active(struct mddev *mddev)
@@ -2273,7 +2380,8 @@ static int narrow_write_error(struct r1bio *r1_bio, int i)
 
 			wbio->bi_vcnt = vcnt;
 		} else {
-			wbio = bio_clone_mddev(r1_bio->master_bio, GFP_NOIO, mddev);
+			wbio = bio_clone_fast(r1_bio->master_bio, GFP_NOIO,
+					      mddev->bio_set);
 		}
 
 		bio_set_op_attrs(wbio, REQ_OP_WRITE, 0);
@@ -2323,8 +2431,9 @@ static void handle_sync_write_finished(struct r1conf *conf, struct r1bio *r1_bio
 
 static void handle_write_finished(struct r1conf *conf, struct r1bio *r1_bio)
 {
-	int m;
+	int m, idx;
 	bool fail = false;
+
 	for (m = 0; m < conf->raid_disks * 2 ; m++)
 		if (r1_bio->bios[m] == IO_MADE_GOOD) {
 			struct md_rdev *rdev = conf->mirrors[m].rdev;
@@ -2350,8 +2459,14 @@ static void handle_write_finished(struct r1conf *conf, struct r1bio *r1_bio)
 	if (fail) {
 		spin_lock_irq(&conf->device_lock);
 		list_add(&r1_bio->retry_list, &conf->bio_end_io_list);
-		conf->nr_queued++;
+		idx = sector_to_idx(r1_bio->sector);
+		atomic_inc(&conf->nr_queued[idx]);
 		spin_unlock_irq(&conf->device_lock);
+		/*
+		 * In case freeze_array() is waiting for condition
+		 * get_unqueued_pending() == extra to be true.
+		 */
+		wake_up(&conf->wait_barrier);
 		md_wakeup_thread(conf->mddev->thread);
 	} else {
 		if (test_bit(R1BIO_WriteError, &r1_bio->state))
@@ -2411,7 +2526,8 @@ static void handle_read_error(struct r1conf *conf, struct r1bio *r1_bio)
 		const unsigned long do_sync
 			= r1_bio->master_bio->bi_opf & REQ_SYNC;
 		r1_bio->read_disk = disk;
-		bio = bio_clone_mddev(r1_bio->master_bio, GFP_NOIO, mddev);
+		bio = bio_clone_fast(r1_bio->master_bio, GFP_NOIO,
+				     mddev->bio_set);
 		bio_trim(bio, r1_bio->sector - bio->bi_iter.bi_sector,
 			 max_sectors);
 		r1_bio->bios[r1_bio->read_disk] = bio;
@@ -2445,15 +2561,8 @@ static void handle_read_error(struct r1conf *conf, struct r1bio *r1_bio)
 			generic_make_request(bio);
 			bio = NULL;
 
-			r1_bio = mempool_alloc(conf->r1bio_pool, GFP_NOIO);
-
-			r1_bio->master_bio = mbio;
-			r1_bio->sectors = bio_sectors(mbio) - sectors_handled;
-			r1_bio->state = 0;
+			r1_bio = alloc_r1bio(mddev, mbio, sectors_handled);
 			set_bit(R1BIO_ReadError, &r1_bio->state);
-			r1_bio->mddev = mddev;
-			r1_bio->sector = mbio->bi_iter.bi_sector +
-				sectors_handled;
 
 			goto read_more;
 		} else {
@@ -2472,6 +2581,7 @@ static void raid1d(struct md_thread *thread)
 	struct r1conf *conf = mddev->private;
 	struct list_head *head = &conf->retry_list;
 	struct blk_plug plug;
+	int idx;
 
 	md_check_recovery(mddev);
 
@@ -2479,17 +2589,15 @@ static void raid1d(struct md_thread *thread)
 	    !test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags)) {
 		LIST_HEAD(tmp);
 		spin_lock_irqsave(&conf->device_lock, flags);
-		if (!test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags)) {
-			while (!list_empty(&conf->bio_end_io_list)) {
-				list_move(conf->bio_end_io_list.prev, &tmp);
-				conf->nr_queued--;
-			}
-		}
+		if (!test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags))
+			list_splice_init(&conf->bio_end_io_list, &tmp);
 		spin_unlock_irqrestore(&conf->device_lock, flags);
 		while (!list_empty(&tmp)) {
 			r1_bio = list_first_entry(&tmp, struct r1bio,
 						  retry_list);
 			list_del(&r1_bio->retry_list);
+			idx = sector_to_idx(r1_bio->sector);
+			atomic_dec(&conf->nr_queued[idx]);
 			if (mddev->degraded)
 				set_bit(R1BIO_Degraded, &r1_bio->state);
 			if (test_bit(R1BIO_WriteError, &r1_bio->state))
@@ -2510,7 +2618,8 @@ static void raid1d(struct md_thread *thread)
 		}
 		r1_bio = list_entry(head->prev, struct r1bio, retry_list);
 		list_del(head->prev);
-		conf->nr_queued--;
+		idx = sector_to_idx(r1_bio->sector);
+		atomic_dec(&conf->nr_queued[idx]);
 		spin_unlock_irqrestore(&conf->device_lock, flags);
 
 		mddev = r1_bio->mddev;
@@ -2549,7 +2658,6 @@ static int init_resync(struct r1conf *conf)
 					  conf->poolinfo);
 	if (!conf->r1buf_pool)
 		return -ENOMEM;
-	conf->next_resync = 0;
 	return 0;
 }
 
@@ -2578,6 +2686,7 @@ static sector_t raid1_sync_request(struct mddev *mddev, sector_t sector_nr,
 	int still_degraded = 0;
 	int good_sectors = RESYNC_SECTORS;
 	int min_bad = 0; /* number of sectors that are bad in all devices */
+	int idx = sector_to_idx(sector_nr);
 
 	if (!conf->r1buf_pool)
 		if (init_resync(conf))
@@ -2627,7 +2736,7 @@ static sector_t raid1_sync_request(struct mddev *mddev, sector_t sector_nr,
 	 * If there is non-resync activity waiting for a turn, then let it
 	 * though before starting on this new sync request.
 	 */
-	if (conf->nr_waiting)
+	if (atomic_read(&conf->nr_waiting[idx]))
 		schedule_timeout_uninterruptible(1);
 
 	/* we are incrementing sector_nr below. To be safe, we check against
@@ -2654,6 +2763,8 @@ static sector_t raid1_sync_request(struct mddev *mddev, sector_t sector_nr,
 	r1_bio->sector = sector_nr;
 	r1_bio->state = 0;
 	set_bit(R1BIO_IsSync, &r1_bio->state);
+	/* make sure good_sectors won't go across barrier unit boundary */
+	good_sectors = align_to_barrier_unit_end(sector_nr, good_sectors);
 
 	for (i = 0; i < conf->raid_disks * 2; i++) {
 		struct md_rdev *rdev;
@@ -2884,6 +2995,26 @@ static struct r1conf *setup_conf(struct mddev *mddev)
 	if (!conf)
 		goto abort;
 
+	conf->nr_pending = kcalloc(BARRIER_BUCKETS_NR,
+				   sizeof(atomic_t), GFP_KERNEL);
+	if (!conf->nr_pending)
+		goto abort;
+
+	conf->nr_waiting = kcalloc(BARRIER_BUCKETS_NR,
+				   sizeof(atomic_t), GFP_KERNEL);
+	if (!conf->nr_waiting)
+		goto abort;
+
+	conf->nr_queued = kcalloc(BARRIER_BUCKETS_NR,
+				  sizeof(atomic_t), GFP_KERNEL);
+	if (!conf->nr_queued)
+		goto abort;
+
+	conf->barrier = kcalloc(BARRIER_BUCKETS_NR,
+				sizeof(atomic_t), GFP_KERNEL);
+	if (!conf->barrier)
+		goto abort;
+
 	conf->mirrors = kzalloc(sizeof(struct raid1_info)
 				* mddev->raid_disks * 2,
 				 GFP_KERNEL);
@@ -2939,9 +3070,6 @@ static struct r1conf *setup_conf(struct mddev *mddev)
 	conf->pending_count = 0;
 	conf->recovery_disabled = mddev->recovery_disabled - 1;
 
-	conf->start_next_window = MaxSector;
-	conf->current_window_requests = conf->next_window_requests = 0;
-
 	err = -EIO;
 	for (i = 0; i < conf->raid_disks * 2; i++) {
 
@@ -2984,6 +3112,10 @@ static struct r1conf *setup_conf(struct mddev *mddev)
 		kfree(conf->mirrors);
 		safe_put_page(conf->tmppage);
 		kfree(conf->poolinfo);
+		kfree(conf->nr_pending);
+		kfree(conf->nr_waiting);
+		kfree(conf->nr_queued);
+		kfree(conf->barrier);
 		kfree(conf);
 	}
 	return ERR_PTR(err);
@@ -3085,6 +3217,10 @@ static void raid1_free(struct mddev *mddev, void *priv)
 	kfree(conf->mirrors);
 	safe_put_page(conf->tmppage);
 	kfree(conf->poolinfo);
+	kfree(conf->nr_pending);
+	kfree(conf->nr_waiting);
+	kfree(conf->nr_queued);
+	kfree(conf->barrier);
 	kfree(conf);
 }
 

drivers/md/raid1.h

 #ifndef _RAID1_H
 #define _RAID1_H
 
+/*
+ * each barrier unit size is 64MB fow now
+ * note: it must be larger than RESYNC_DEPTH
+ */
+#define BARRIER_UNIT_SECTOR_BITS	17
+#define BARRIER_UNIT_SECTOR_SIZE	(1<<17)
+/*
+ * In struct r1conf, the following members are related to I/O barrier
+ * buckets,
+ *	atomic_t	*nr_pending;
+ *	atomic_t	*nr_waiting;
+ *	atomic_t	*nr_queued;
+ *	atomic_t	*barrier;
+ * Each of them points to array of atomic_t variables, each array is
+ * designed to have BARRIER_BUCKETS_NR elements and occupy a single
+ * memory page. The data width of atomic_t variables is 4 bytes, equal
+ * to 1<<(ilog2(sizeof(atomic_t))), BARRIER_BUCKETS_NR_BITS is defined
+ * as (PAGE_SHIFT - ilog2(sizeof(int))) to make sure an array of
+ * atomic_t variables with BARRIER_BUCKETS_NR elements just exactly
+ * occupies a single memory page.
+ */
+#define BARRIER_BUCKETS_NR_BITS		(PAGE_SHIFT - ilog2(sizeof(atomic_t)))
+#define BARRIER_BUCKETS_NR		(1<<BARRIER_BUCKETS_NR_BITS)
+
 struct raid1_info {
 	struct md_rdev	*rdev;
 	sector_t	head_position;
@@ -35,25 +59,6 @@ struct r1conf {
 						 */
 	int			raid_disks;
 
-	/* During resync, read_balancing is only allowed on the part
-	 * of the array that has been resynced.  'next_resync' tells us
-	 * where that is.
-	 */
-	sector_t		next_resync;
-
-	/* When raid1 starts resync, we divide array into four partitions
-	 * |---------|--------------|---------------------|-------------|
-	 *        next_resync   start_next_window       end_window
-	 * start_next_window = next_resync + NEXT_NORMALIO_DISTANCE
-	 * end_window = start_next_window + NEXT_NORMALIO_DISTANCE
-	 * current_window_requests means the count of normalIO between
-	 *   start_next_window and end_window.
-	 * next_window_requests means the count of normalIO after end_window.
-	 * */
-	sector_t		start_next_window;
-	int			current_window_requests;
-	int			next_window_requests;
-
 	spinlock_t		device_lock;
 
 	/* list of 'struct r1bio' that need to be processed by raid1d,
@@ -79,10 +84,10 @@ struct r1conf {
 	 */
 	wait_queue_head_t	wait_barrier;
 	spinlock_t		resync_lock;
-	int			nr_pending;
-	int			nr_waiting;
-	int			nr_queued;
-	int			barrier;
+	atomic_t		*nr_pending;
+	atomic_t		*nr_waiting;
+	atomic_t		*nr_queued;
+	atomic_t		*barrier;
 	int			array_frozen;
 
 	/* Set to 1 if a full sync is needed, (fresh device added).
@@ -135,7 +140,6 @@ struct r1bio {
 						 * in this BehindIO request
 						 */
 	sector_t		sector;
-	sector_t		start_next_window;
 	int			sectors;
 	unsigned long		state;
 	struct mddev		*mddev;
@@ -185,4 +189,10 @@ enum r1bio_state {
 	R1BIO_WriteError,
 	R1BIO_FailFast,
 };
+
+static inline int sector_to_idx(sector_t sector)
+{
+	return hash_long(sector >> BARRIER_UNIT_SECTOR_BITS,
+			 BARRIER_BUCKETS_NR_BITS);
+}
 #endif

drivers/md/raid10.c

@@ -1132,7 +1132,7 @@ static void raid10_read_request(struct mddev *mddev, struct bio *bio,
 	}
 	slot = r10_bio->read_slot;
 
-	read_bio = bio_clone_mddev(bio, GFP_NOIO, mddev);
+	read_bio = bio_clone_fast(bio, GFP_NOIO, mddev->bio_set);
 	bio_trim(read_bio, r10_bio->sector - bio->bi_iter.bi_sector,
 		 max_sectors);
 
@@ -1406,7 +1406,7 @@ static void raid10_write_request(struct mddev *mddev, struct bio *bio,
 		int d = r10_bio->devs[i].devnum;
 		if (r10_bio->devs[i].bio) {
 			struct md_rdev *rdev = conf->mirrors[d].rdev;
-			mbio = bio_clone_mddev(bio, GFP_NOIO, mddev);
+			mbio = bio_clone_fast(bio, GFP_NOIO, mddev->bio_set);
 			bio_trim(mbio, r10_bio->sector - bio->bi_iter.bi_sector,
 				 max_sectors);
 			r10_bio->devs[i].bio = mbio;
@@ -1457,7 +1457,7 @@ static void raid10_write_request(struct mddev *mddev, struct bio *bio,
 				smp_mb();
 				rdev = conf->mirrors[d].rdev;
 			}
-			mbio = bio_clone_mddev(bio, GFP_NOIO, mddev);
+			mbio = bio_clone_fast(bio, GFP_NOIO, mddev->bio_set);
 			bio_trim(mbio, r10_bio->sector - bio->bi_iter.bi_sector,
 				 max_sectors);
 			r10_bio->devs[i].repl_bio = mbio;
@@ -2565,7 +2565,7 @@ static int narrow_write_error(struct r10bio *r10_bio, int i)
 		if (sectors > sect_to_write)
 			sectors = sect_to_write;
 		/* Write at 'sector' for 'sectors' */
-		wbio = bio_clone_mddev(bio, GFP_NOIO, mddev);
+		wbio = bio_clone_fast(bio, GFP_NOIO, mddev->bio_set);
 		bio_trim(wbio, sector - bio->bi_iter.bi_sector, sectors);
 		wsector = r10_bio->devs[i].addr + (sector - r10_bio->sector);
 		wbio->bi_iter.bi_sector = wsector +
@@ -2641,8 +2641,7 @@ static void handle_read_error(struct mddev *mddev, struct r10bio *r10_bio)
 			   mdname(mddev),
 			   bdevname(rdev->bdev, b),
 			   (unsigned long long)r10_bio->sector);
-	bio = bio_clone_mddev(r10_bio->master_bio,
-			      GFP_NOIO, mddev);
+	bio = bio_clone_fast(r10_bio->master_bio, GFP_NOIO, mddev->bio_set);
 	bio_trim(bio, r10_bio->sector - bio->bi_iter.bi_sector, max_sectors);
 	r10_bio->devs[slot].bio = bio;
 	r10_bio->devs[slot].rdev = rdev;

drivers/md/raid5-cache.c

@@ -20,6 +20,7 @@
 #include <linux/crc32c.h>
 #include <linux/random.h>
 #include <linux/kthread.h>
+#include <linux/types.h>
 #include "md.h"
 #include "raid5.h"
 #include "bitmap.h"
@@ -164,8 +165,59 @@ struct r5l_log {
 	struct work_struct deferred_io_work;
 	/* to disable write back during in degraded mode */
 	struct work_struct disable_writeback_work;
+
+	/* to for chunk_aligned_read in writeback mode, details below */
+	spinlock_t tree_lock;
+	struct radix_tree_root big_stripe_tree;
 };
 
+/*
+ * Enable chunk_aligned_read() with write back cache.
+ *
+ * Each chunk may contain more than one stripe (for example, a 256kB
+ * chunk contains 64 4kB-page, so this chunk contain 64 stripes). For
+ * chunk_aligned_read, these stripes are grouped into one "big_stripe".
+ * For each big_stripe, we count how many stripes of this big_stripe
+ * are in the write back cache. These data are tracked in a radix tree
+ * (big_stripe_tree). We use radix_tree item pointer as the counter.
+ * r5c_tree_index() is used to calculate keys for the radix tree.
+ *
+ * chunk_aligned_read() calls r5c_big_stripe_cached() to look up
+ * big_stripe of each chunk in the tree. If this big_stripe is in the
+ * tree, chunk_aligned_read() aborts. This look up is protected by
+ * rcu_read_lock().
+ *
+ * It is necessary to remember whether a stripe is counted in
+ * big_stripe_tree. Instead of adding new flag, we reuses existing flags:
+ * STRIPE_R5C_PARTIAL_STRIPE and STRIPE_R5C_FULL_STRIPE. If either of these
+ * two flags are set, the stripe is counted in big_stripe_tree. This
+ * requires moving set_bit(STRIPE_R5C_PARTIAL_STRIPE) to
+ * r5c_try_caching_write(); and moving clear_bit of
+ * STRIPE_R5C_PARTIAL_STRIPE and STRIPE_R5C_FULL_STRIPE to
+ * r5c_finish_stripe_write_out().
+ */
+
+/*
+ * radix tree requests lowest 2 bits of data pointer to be 2b'00.
+ * So it is necessary to left shift the counter by 2 bits before using it
+ * as data pointer of the tree.
+ */
+#define R5C_RADIX_COUNT_SHIFT 2
+
+/*
+ * calculate key for big_stripe_tree
+ *
+ * sect: align_bi->bi_iter.bi_sector or sh->sector
+ */
+static inline sector_t r5c_tree_index(struct r5conf *conf,
+				      sector_t sect)
+{
+	sector_t offset;
+
+	offset = sector_div(sect, conf->chunk_sectors);
+	return sect;
+}
+
 /*
  * an IO range starts from a meta data block and end at the next meta data
  * block. The io unit's the meta data block tracks data/parity followed it. io
@@ -337,17 +389,30 @@ void r5c_check_cached_full_stripe(struct r5conf *conf)
 /*
  * Total log space (in sectors) needed to flush all data in cache
  *
- * Currently, writing-out phase automatically includes all pending writes
- * to the same sector. So the reclaim of each stripe takes up to
- * (conf->raid_disks + 1) pages of log space.
+ * To avoid deadlock due to log space, it is necessary to reserve log
+ * space to flush critical stripes (stripes that occupying log space near
+ * last_checkpoint). This function helps check how much log space is
+ * required to flush all cached stripes.
  *
- * To totally avoid deadlock due to log space, the code reserves
- * (conf->raid_disks + 1) pages for each stripe in cache, which is not
- * necessary in most cases.
+ * To reduce log space requirements, two mechanisms are used to give cache
+ * flush higher priorities:
+ *    1. In handle_stripe_dirtying() and schedule_reconstruction(),
+ *       stripes ALREADY in journal can be flushed w/o pending writes;
+ *    2. In r5l_write_stripe() and r5c_cache_data(), stripes NOT in journal
+ *       can be delayed (r5l_add_no_space_stripe).
  *
- * To improve this, we will need writing-out phase to be able to NOT include
- * pending writes, which will reduce the requirement to
- * (conf->max_degraded + 1) pages per stripe in cache.
+ * In cache flush, the stripe goes through 1 and then 2. For a stripe that
+ * already passed 1, flushing it requires at most (conf->max_degraded + 1)
+ * pages of journal space. For stripes that has not passed 1, flushing it
+ * requires (conf->raid_disks + 1) pages of journal space. There are at
+ * most (conf->group_cnt + 1) stripe that passed 1. So total journal space
+ * required to flush all cached stripes (in pages) is:
+ *
+ *     (stripe_in_journal_count - group_cnt - 1) * (max_degraded + 1) +
+ *     (group_cnt + 1) * (raid_disks + 1)
+ * or
+ *     (stripe_in_journal_count) * (max_degraded + 1) +
+ *     (group_cnt + 1) * (raid_disks - max_degraded)
  */
 static sector_t r5c_log_required_to_flush_cache(struct r5conf *conf)
 {
@@ -356,8 +421,9 @@ static sector_t r5c_log_required_to_flush_cache(struct r5conf *conf)
 	if (!r5c_is_writeback(log))
 		return 0;
 
-	return BLOCK_SECTORS * (conf->raid_disks + 1) *
-		atomic_read(&log->stripe_in_journal_count);
+	return BLOCK_SECTORS *
+		((conf->max_degraded + 1) * atomic_read(&log->stripe_in_journal_count) +
+		 (conf->raid_disks - conf->max_degraded) * (conf->group_cnt + 1));
 }
 
 /*
@@ -412,16 +478,6 @@ void r5c_make_stripe_write_out(struct stripe_head *sh)
 
 	if (!test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
 		atomic_inc(&conf->preread_active_stripes);
-
-	if (test_and_clear_bit(STRIPE_R5C_PARTIAL_STRIPE, &sh->state)) {
-		BUG_ON(atomic_read(&conf->r5c_cached_partial_stripes) == 0);
-		atomic_dec(&conf->r5c_cached_partial_stripes);
-	}
-
-	if (test_and_clear_bit(STRIPE_R5C_FULL_STRIPE, &sh->state)) {
-		BUG_ON(atomic_read(&conf->r5c_cached_full_stripes) == 0);
-		atomic_dec(&conf->r5c_cached_full_stripes);
-	}
 }
 
 static void r5c_handle_data_cached(struct stripe_head *sh)
@@ -1271,6 +1327,10 @@ static void r5c_flush_stripe(struct r5conf *conf, struct stripe_head *sh)
 	atomic_inc(&conf->active_stripes);
 	r5c_make_stripe_write_out(sh);
 
+	if (test_bit(STRIPE_R5C_PARTIAL_STRIPE, &sh->state))
+		atomic_inc(&conf->r5c_flushing_partial_stripes);
+	else
+		atomic_inc(&conf->r5c_flushing_full_stripes);
 	raid5_release_stripe(sh);
 }
 
@@ -1313,12 +1373,16 @@ static void r5c_do_reclaim(struct r5conf *conf)
 	unsigned long flags;
 	int total_cached;
 	int stripes_to_flush;
+	int flushing_partial, flushing_full;
 
 	if (!r5c_is_writeback(log))
 		return;
 
+	flushing_partial = atomic_read(&conf->r5c_flushing_partial_stripes);
+	flushing_full = atomic_read(&conf->r5c_flushing_full_stripes);
 	total_cached = atomic_read(&conf->r5c_cached_partial_stripes) +
-		atomic_read(&conf->r5c_cached_full_stripes);
+		atomic_read(&conf->r5c_cached_full_stripes) -
+		flushing_full - flushing_partial;
 
 	if (total_cached > conf->min_nr_stripes * 3 / 4 ||
 	    atomic_read(&conf->empty_inactive_list_nr) > 0)
@@ -1328,7 +1392,7 @@ static void r5c_do_reclaim(struct r5conf *conf)
 		 */
 		stripes_to_flush = R5C_RECLAIM_STRIPE_GROUP;
 	else if (total_cached > conf->min_nr_stripes * 1 / 2 ||
-		 atomic_read(&conf->r5c_cached_full_stripes) >
+		 atomic_read(&conf->r5c_cached_full_stripes) - flushing_full >
 		 R5C_FULL_STRIPE_FLUSH_BATCH)
 		/*
 		 * if stripe cache pressure moderate, or if there is many full
@@ -1362,10 +1426,10 @@ static void r5c_do_reclaim(struct r5conf *conf)
 			    !test_bit(STRIPE_HANDLE, &sh->state) &&
 			    atomic_read(&sh->count) == 0) {
 				r5c_flush_stripe(conf, sh);
-			}
 				if (count++ >= R5C_RECLAIM_STRIPE_GROUP)
 					break;
 			}
+		}
 		spin_unlock(&conf->device_lock);
 		spin_unlock_irqrestore(&log->stripe_in_journal_lock, flags);
 	}
@@ -2320,6 +2384,10 @@ int r5c_try_caching_write(struct r5conf *conf,
 	int i;
 	struct r5dev *dev;
 	int to_cache = 0;
+	void **pslot;
+	sector_t tree_index;
+	int ret;
+	uintptr_t refcount;
 
 	BUG_ON(!r5c_is_writeback(log));
 
@@ -2364,6 +2432,44 @@ int r5c_try_caching_write(struct r5conf *conf,
 		}
 	}
 
+	/* if the stripe is not counted in big_stripe_tree, add it now */
+	if (!test_bit(STRIPE_R5C_PARTIAL_STRIPE, &sh->state) &&
+	    !test_bit(STRIPE_R5C_FULL_STRIPE, &sh->state)) {
+		tree_index = r5c_tree_index(conf, sh->sector);
+		spin_lock(&log->tree_lock);
+		pslot = radix_tree_lookup_slot(&log->big_stripe_tree,
+					       tree_index);
+		if (pslot) {
+			refcount = (uintptr_t)radix_tree_deref_slot_protected(
+				pslot, &log->tree_lock) >>
+				R5C_RADIX_COUNT_SHIFT;
+			radix_tree_replace_slot(
+				&log->big_stripe_tree, pslot,
+				(void *)((refcount + 1) << R5C_RADIX_COUNT_SHIFT));
+		} else {
+			/*
+			 * this radix_tree_insert can fail safely, so no
+			 * need to call radix_tree_preload()
+			 */
+			ret = radix_tree_insert(
+				&log->big_stripe_tree, tree_index,
+				(void *)(1 << R5C_RADIX_COUNT_SHIFT));
+			if (ret) {
+				spin_unlock(&log->tree_lock);
+				r5c_make_stripe_write_out(sh);
+				return -EAGAIN;
+			}
+		}
+		spin_unlock(&log->tree_lock);
+
+		/*
+		 * set STRIPE_R5C_PARTIAL_STRIPE, this shows the stripe is
+		 * counted in the radix tree
+		 */
+		set_bit(STRIPE_R5C_PARTIAL_STRIPE, &sh->state);
+		atomic_inc(&conf->r5c_cached_partial_stripes);
+	}
+
 	for (i = disks; i--; ) {
 		dev = &sh->dev[i];
 		if (dev->towrite) {
@@ -2438,17 +2544,20 @@ void r5c_finish_stripe_write_out(struct r5conf *conf,
 				 struct stripe_head *sh,
 				 struct stripe_head_state *s)
 {
+	struct r5l_log *log = conf->log;
 	int i;
 	int do_wakeup = 0;
+	sector_t tree_index;
+	void **pslot;
+	uintptr_t refcount;
 
-	if (!conf->log ||
-	    !test_bit(R5_InJournal, &sh->dev[sh->pd_idx].flags))
+	if (!log || !test_bit(R5_InJournal, &sh->dev[sh->pd_idx].flags))
 		return;
 
 	WARN_ON(test_bit(STRIPE_R5C_CACHING, &sh->state));
 	clear_bit(R5_InJournal, &sh->dev[sh->pd_idx].flags);
 
-	if (conf->log->r5c_journal_mode == R5C_JOURNAL_MODE_WRITE_THROUGH)
+	if (log->r5c_journal_mode == R5C_JOURNAL_MODE_WRITE_THROUGH)
 		return;
 
 	for (i = sh->disks; i--; ) {
@@ -2470,12 +2579,45 @@ void r5c_finish_stripe_write_out(struct r5conf *conf,
 	if (do_wakeup)
 		wake_up(&conf->wait_for_overlap);
 
-	spin_lock_irq(&conf->log->stripe_in_journal_lock);
+	spin_lock_irq(&log->stripe_in_journal_lock);
 	list_del_init(&sh->r5c);
-	spin_unlock_irq(&conf->log->stripe_in_journal_lock);
+	spin_unlock_irq(&log->stripe_in_journal_lock);
 	sh->log_start = MaxSector;
-	atomic_dec(&conf->log->stripe_in_journal_count);
-	r5c_update_log_state(conf->log);
+
+	atomic_dec(&log->stripe_in_journal_count);
+	r5c_update_log_state(log);
+
+	/* stop counting this stripe in big_stripe_tree */
+	if (test_bit(STRIPE_R5C_PARTIAL_STRIPE, &sh->state) ||
+	    test_bit(STRIPE_R5C_FULL_STRIPE, &sh->state)) {
+		tree_index = r5c_tree_index(conf, sh->sector);
+		spin_lock(&log->tree_lock);
+		pslot = radix_tree_lookup_slot(&log->big_stripe_tree,
+					       tree_index);
+		BUG_ON(pslot == NULL);
+		refcount = (uintptr_t)radix_tree_deref_slot_protected(
+			pslot, &log->tree_lock) >>
+			R5C_RADIX_COUNT_SHIFT;
+		if (refcount == 1)
+			radix_tree_delete(&log->big_stripe_tree, tree_index);
+		else
+			radix_tree_replace_slot(
+				&log->big_stripe_tree, pslot,
+				(void *)((refcount - 1) << R5C_RADIX_COUNT_SHIFT));
+		spin_unlock(&log->tree_lock);
+	}
+
+	if (test_and_clear_bit(STRIPE_R5C_PARTIAL_STRIPE, &sh->state)) {
+		BUG_ON(atomic_read(&conf->r5c_cached_partial_stripes) == 0);
+		atomic_dec(&conf->r5c_flushing_partial_stripes);
+		atomic_dec(&conf->r5c_cached_partial_stripes);
+	}
+
+	if (test_and_clear_bit(STRIPE_R5C_FULL_STRIPE, &sh->state)) {
+		BUG_ON(atomic_read(&conf->r5c_cached_full_stripes) == 0);
+		atomic_dec(&conf->r5c_flushing_full_stripes);
+		atomic_dec(&conf->r5c_cached_full_stripes);
+	}
 }
 
 int
@@ -2535,6 +2677,22 @@ r5c_cache_data(struct r5l_log *log, struct stripe_head *sh,
 	return 0;
 }
 
+/* check whether this big stripe is in write back cache. */
+bool r5c_big_stripe_cached(struct r5conf *conf, sector_t sect)
+{
+	struct r5l_log *log = conf->log;
+	sector_t tree_index;
+	void *slot;
+
+	if (!log)
+		return false;
+
+	WARN_ON_ONCE(!rcu_read_lock_held());
+	tree_index = r5c_tree_index(conf, sect);
+	slot = radix_tree_lookup(&log->big_stripe_tree, tree_index);
+	return slot != NULL;
+}
+
 static int r5l_load_log(struct r5l_log *log)
 {
 	struct md_rdev *rdev = log->rdev;
@@ -2681,6 +2839,9 @@ int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
 	if (!log->meta_pool)
 		goto out_mempool;
 
+	spin_lock_init(&log->tree_lock);
+	INIT_RADIX_TREE(&log->big_stripe_tree, GFP_NOWAIT | __GFP_NOWARN);
+
 	log->reclaim_thread = md_register_thread(r5l_reclaim_thread,
 						 log->rdev->mddev, "reclaim");
 	if (!log->reclaim_thread)

drivers/md/raid5.c

@@ -281,16 +281,16 @@ static void do_release_stripe(struct r5conf *conf, struct stripe_head *sh,
 						atomic_dec(&conf->r5c_cached_partial_stripes);
 					list_add_tail(&sh->lru, &conf->r5c_full_stripe_list);
 					r5c_check_cached_full_stripe(conf);
-				} else {
-					/* partial stripe */
-					if (!test_and_set_bit(STRIPE_R5C_PARTIAL_STRIPE,
-							      &sh->state))
-						atomic_inc(&conf->r5c_cached_partial_stripes);
+				} else
+					/*
+					 * STRIPE_R5C_PARTIAL_STRIPE is set in
+					 * r5c_try_caching_write(). No need to
+					 * set it again.
+					 */
 					list_add_tail(&sh->lru, &conf->r5c_partial_stripe_list);
 			}
 		}
 	}
-	}
 }
 
 static void __release_stripe(struct r5conf *conf, struct stripe_head *sh,
@@ -353,17 +353,15 @@ static void release_inactive_stripe_list(struct r5conf *conf,
 static int release_stripe_list(struct r5conf *conf,
 			       struct list_head *temp_inactive_list)
 {
-	struct stripe_head *sh;
+	struct stripe_head *sh, *t;
 	int count = 0;
 	struct llist_node *head;
 
 	head = llist_del_all(&conf->released_stripes);
 	head = llist_reverse_order(head);
-	while (head) {
+	llist_for_each_entry_safe(sh, t, head, release_list) {
 		int hash;
 
-		sh = llist_entry(head, struct stripe_head, release_list);
-		head = llist_next(head);
 		/* sh could be readded after STRIPE_ON_RELEASE_LIST is cleard */
 		smp_mb();
 		clear_bit(STRIPE_ON_RELEASE_LIST, &sh->state);
@@ -863,6 +861,43 @@ static int use_new_offset(struct r5conf *conf, struct stripe_head *sh)
 	return 1;
 }
 
+static void flush_deferred_bios(struct r5conf *conf)
+{
+	struct bio_list tmp;
+	struct bio *bio;
+
+	if (!conf->batch_bio_dispatch || !conf->group_cnt)
+		return;
+
+	bio_list_init(&tmp);
+	spin_lock(&conf->pending_bios_lock);
+	bio_list_merge(&tmp, &conf->pending_bios);
+	bio_list_init(&conf->pending_bios);
+	spin_unlock(&conf->pending_bios_lock);
+
+	while ((bio = bio_list_pop(&tmp)))
+		generic_make_request(bio);
+}
+
+static void defer_bio_issue(struct r5conf *conf, struct bio *bio)
+{
+	/*
+	 * change group_cnt will drain all bios, so this is safe
+	 *
+	 * A read generally means a read-modify-write, which usually means a
+	 * randwrite, so we don't delay it
+	 */
+	if (!conf->batch_bio_dispatch || !conf->group_cnt ||
+	    bio_op(bio) == REQ_OP_READ) {
+		generic_make_request(bio);
+		return;
+	}
+	spin_lock(&conf->pending_bios_lock);
+	bio_list_add(&conf->pending_bios, bio);
+	spin_unlock(&conf->pending_bios_lock);
+	md_wakeup_thread(conf->mddev->thread);
+}
+
 static void
 raid5_end_read_request(struct bio *bi);
 static void
@@ -1043,7 +1078,7 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
 				trace_block_bio_remap(bdev_get_queue(bi->bi_bdev),
 						      bi, disk_devt(conf->mddev->gendisk),
 						      sh->dev[i].sector);
-			generic_make_request(bi);
+			defer_bio_issue(conf, bi);
 		}
 		if (rrdev) {
 			if (s->syncing || s->expanding || s->expanded
@@ -1088,7 +1123,7 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
 				trace_block_bio_remap(bdev_get_queue(rbi->bi_bdev),
 						      rbi, disk_devt(conf->mddev->gendisk),
 						      sh->dev[i].sector);
-			generic_make_request(rbi);
+			defer_bio_issue(conf, rbi);
 		}
 		if (!rdev && !rrdev) {
 			if (op_is_write(op))
@@ -2914,12 +2949,36 @@ sector_t raid5_compute_blocknr(struct stripe_head *sh, int i, int previous)
  *      like to flush data in journal to RAID disks first, so complex rmw
  *      is handled in the write patch (handle_stripe_dirtying).
  *
+ *   2. when journal space is critical (R5C_LOG_CRITICAL=1)
+ *
+ *      It is important to be able to flush all stripes in raid5-cache.
+ *      Therefore, we need reserve some space on the journal device for
+ *      these flushes. If flush operation includes pending writes to the
+ *      stripe, we need to reserve (conf->raid_disk + 1) pages per stripe
+ *      for the flush out. If we exclude these pending writes from flush
+ *      operation, we only need (conf->max_degraded + 1) pages per stripe.
+ *      Therefore, excluding pending writes in these cases enables more
+ *      efficient use of the journal device.
+ *
+ *      Note: To make sure the stripe makes progress, we only delay
+ *      towrite for stripes with data already in journal (injournal > 0).
+ *      When LOG_CRITICAL, stripes with injournal == 0 will be sent to
+ *      no_space_stripes list.
+ *
  */
-static inline bool delay_towrite(struct r5dev *dev,
+static inline bool delay_towrite(struct r5conf *conf,
+				 struct r5dev *dev,
 				 struct stripe_head_state *s)
 {
-	return !test_bit(R5_OVERWRITE, &dev->flags) &&
-		!test_bit(R5_Insync, &dev->flags) && s->injournal;
+	/* case 1 above */
+	if (!test_bit(R5_OVERWRITE, &dev->flags) &&
+	    !test_bit(R5_Insync, &dev->flags) && s->injournal)
+		return true;
+	/* case 2 above */
+	if (test_bit(R5C_LOG_CRITICAL, &conf->cache_state) &&
+	    s->injournal > 0)
+		return true;
+	return false;
 }
 
 static void
@@ -2942,7 +3001,7 @@ schedule_reconstruction(struct stripe_head *sh, struct stripe_head_state *s,
 		for (i = disks; i--; ) {
 			struct r5dev *dev = &sh->dev[i];
 
-			if (dev->towrite && !delay_towrite(dev, s)) {
+			if (dev->towrite && !delay_towrite(conf, dev, s)) {
 				set_bit(R5_LOCKED, &dev->flags);
 				set_bit(R5_Wantdrain, &dev->flags);
 				if (!expand)
@@ -3694,7 +3753,7 @@ static int handle_stripe_dirtying(struct r5conf *conf,
 	} else for (i = disks; i--; ) {
 		/* would I have to read this buffer for read_modify_write */
 		struct r5dev *dev = &sh->dev[i];
-		if (((dev->towrite && !delay_towrite(dev, s)) ||
+		if (((dev->towrite && !delay_towrite(conf, dev, s)) ||
 		     i == sh->pd_idx || i == sh->qd_idx ||
 		     test_bit(R5_InJournal, &dev->flags)) &&
 		    !test_bit(R5_LOCKED, &dev->flags) &&
@@ -3718,8 +3777,8 @@ static int handle_stripe_dirtying(struct r5conf *conf,
 		}
 	}
 
-	pr_debug("for sector %llu, rmw=%d rcw=%d\n",
-		(unsigned long long)sh->sector, rmw, rcw);
+	pr_debug("for sector %llu state 0x%lx, rmw=%d rcw=%d\n",
+		 (unsigned long long)sh->sector, sh->state, rmw, rcw);
 	set_bit(STRIPE_HANDLE, &sh->state);
 	if ((rmw < rcw || (rmw == rcw && conf->rmw_level == PARITY_PREFER_RMW)) && rmw > 0) {
 		/* prefer read-modify-write, but need to get some data */
@@ -3759,7 +3818,7 @@ static int handle_stripe_dirtying(struct r5conf *conf,
 
 		for (i = disks; i--; ) {
 			struct r5dev *dev = &sh->dev[i];
-			if (((dev->towrite && !delay_towrite(dev, s)) ||
+			if (((dev->towrite && !delay_towrite(conf, dev, s)) ||
 			     i == sh->pd_idx || i == sh->qd_idx ||
 			     test_bit(R5_InJournal, &dev->flags)) &&
 			    !test_bit(R5_LOCKED, &dev->flags) &&
@@ -4995,9 +5054,9 @@ static int raid5_read_one_chunk(struct mddev *mddev, struct bio *raid_bio)
 		return 0;
 	}
 	/*
-	 * use bio_clone_mddev to make a copy of the bio
+	 * use bio_clone_fast to make a copy of the bio
 	 */
-	align_bi = bio_clone_mddev(raid_bio, GFP_NOIO, mddev);
+	align_bi = bio_clone_fast(raid_bio, GFP_NOIO, mddev->bio_set);
 	if (!align_bi)
 		return 0;
 	/*
@@ -5025,6 +5084,13 @@ static int raid5_read_one_chunk(struct mddev *mddev, struct bio *raid_bio)
 		      rdev->recovery_offset >= end_sector)))
 			rdev = NULL;
 	}
+
+	if (r5c_big_stripe_cached(conf, align_bi->bi_iter.bi_sector)) {
+		rcu_read_unlock();
+		bio_put(align_bi);
+		return 0;
+	}
+
 	if (rdev) {
 		sector_t first_bad;
 		int bad_sectors;
@@ -5381,7 +5447,6 @@ static void raid5_make_request(struct mddev *mddev, struct bio * bi)
 	 * data on failed drives.
 	 */
 	if (rw == READ && mddev->degraded == 0 &&
-	    !r5c_is_writeback(conf->log) &&
 	    mddev->reshape_position == MaxSector) {
 		bi = chunk_aligned_read(mddev, bi);
 		if (!bi)
@@ -6126,6 +6191,8 @@ static void raid5d(struct md_thread *thread)
 		mutex_unlock(&conf->cache_size_mutex);
 	}
 
+	flush_deferred_bios(conf);
+
 	r5l_flush_stripe_to_raid(conf->log);
 
 	async_tx_issue_pending_all();
@@ -6711,6 +6778,18 @@ static struct r5conf *setup_conf(struct mddev *mddev)
 	atomic_set(&conf->active_stripes, 0);
 	atomic_set(&conf->preread_active_stripes, 0);
 	atomic_set(&conf->active_aligned_reads, 0);
+	bio_list_init(&conf->pending_bios);
+	spin_lock_init(&conf->pending_bios_lock);
+	conf->batch_bio_dispatch = true;
+	rdev_for_each(rdev, mddev) {
+		if (test_bit(Journal, &rdev->flags))
+			continue;
+		if (blk_queue_nonrot(bdev_get_queue(rdev->bdev))) {
+			conf->batch_bio_dispatch = false;
+			break;
+		}
+	}
+
 	conf->bypass_threshold = BYPASS_THRESHOLD;
 	conf->recovery_disabled = mddev->recovery_disabled - 1;
 
@@ -6757,6 +6836,8 @@ static struct r5conf *setup_conf(struct mddev *mddev)
 	INIT_LIST_HEAD(&conf->r5c_full_stripe_list);
 	atomic_set(&conf->r5c_cached_partial_stripes, 0);
 	INIT_LIST_HEAD(&conf->r5c_partial_stripe_list);
+	atomic_set(&conf->r5c_flushing_full_stripes, 0);
+	atomic_set(&conf->r5c_flushing_partial_stripes, 0);
 
 	conf->level = mddev->new_level;
 	conf->chunk_sectors = mddev->new_chunk_sectors;

drivers/md/raid5.h

@@ -663,6 +663,8 @@ struct r5conf {
 	struct list_head	r5c_full_stripe_list;
 	atomic_t		r5c_cached_partial_stripes;
 	struct list_head	r5c_partial_stripe_list;
+	atomic_t		r5c_flushing_full_stripes;
+	atomic_t		r5c_flushing_partial_stripes;
 
 	atomic_t		empty_inactive_list_nr;
 	struct llist_head	released_stripes;
@@ -684,6 +686,10 @@ struct r5conf {
 	int			group_cnt;
 	int			worker_cnt_per_group;
 	struct r5l_log		*log;
+
+	struct bio_list		pending_bios;
+	spinlock_t		pending_bios_lock;
+	bool			batch_bio_dispatch;
 };
 
 
@@ -788,4 +794,5 @@ extern void r5c_check_stripe_cache_usage(struct r5conf *conf);
 extern void r5c_check_cached_full_stripe(struct r5conf *conf);
 extern struct md_sysfs_entry r5c_journal_mode;
 extern void r5c_update_on_rdev_error(struct mddev *mddev);
+extern bool r5c_big_stripe_cached(struct r5conf *conf, sector_t sect);
 #endif

include/linux/bio.h

@@ -183,7 +183,7 @@ static inline void bio_advance_iter(struct bio *bio, struct bvec_iter *iter,
 
 #define bio_iter_last(bvec, iter) ((iter).bi_size == (bvec).bv_len)
 
-static inline unsigned bio_segments(struct bio *bio)
+static inline unsigned __bio_segments(struct bio *bio, struct bvec_iter *bvec)
 {
 	unsigned segs = 0;
 	struct bio_vec bv;
@@ -205,12 +205,17 @@ static inline unsigned bio_segments(struct bio *bio)
 		break;
 	}
 
-	bio_for_each_segment(bv, bio, iter)
+	__bio_for_each_segment(bv, bio, iter, *bvec)
 		segs++;
 
 	return segs;
 }
 
+static inline unsigned bio_segments(struct bio *bio)
+{
+	return __bio_segments(bio, &bio->bi_iter);
+}
+
 /*
  * get a reference to a bio, so it won't disappear. the intended use is
  * something like:
@@ -384,6 +389,8 @@ extern void bio_put(struct bio *);
 extern void __bio_clone_fast(struct bio *, struct bio *);
 extern struct bio *bio_clone_fast(struct bio *, gfp_t, struct bio_set *);
 extern struct bio *bio_clone_bioset(struct bio *, gfp_t, struct bio_set *bs);
+extern struct bio *bio_clone_bioset_partial(struct bio *, gfp_t,
+					    struct bio_set *, int, int);
 
 extern struct bio_set *fs_bio_set;
 

lib/radix-tree.c

@@ -1102,6 +1102,7 @@ void radix_tree_replace_slot(struct radix_tree_root *root,
 {
 	replace_slot(root, NULL, slot, item, true);
 }
+EXPORT_SYMBOL(radix_tree_replace_slot);
 
 /**
  * radix_tree_iter_replace - replace item in a slot