[PATCH v4 0/8] raid5-cache: enabling cache features

[PATCH v4 0/8] raid5-cache: enabling cache features

[Song Liu]

These are the 4th version of patches to enable write cache part of
raid5-cache. The journal part was released with kernel 4.4.

The caching part uses same disk format of raid456 journal, and provides
acceleration to writes. Write operations are committed (bio_endio) once
the data is secured in journal. Reconstruct and RMW are postponed to
reclaim path, which is (hopefully) not on the critical path.

The changes are organized in 8 patches (details below).

Patch for chunk_aligned_read in earlier RFC is not included yet
(http://marc.info/?l=linux-raid&m=146432700719277). But we may still need
some optimizations later, especially for SSD raid devices.

Changes from PATCH v3 (http://marc.info/?l=linux-raid&m=147573807306070):
  1. Make reclaim robust
  2. Fix a bug in recovery

Changes between v3 and v2 (http://marc.info/?l=linux-raid&m=147493266208102):
  1. Incorporate feedback from Shaohua
  2. Reorganize the patches, for hopefully easier review
  3. Make sure no change to write through mode (journal only)
  4. Change reclaim design to avoid deadlock due to log space

Thanks,
Song

Song Liu (8):
  md/r5cache: Check array size in r5l_init_log
  md/r5cache: move some code to raid5.h
  md/r5cache: State machine for raid5-cache write back mode
  md/r5cache: write part of r5cache
  md/r5cache: reclaim support
  md/r5cache: sysfs entry r5c_state
  md/r5cache: r5c recovery
  md/r5cache: handle SYNC and FUA

 drivers/md/raid5-cache.c | 1593 ++++++++++++++++++++++++++++++++++++++++------
 drivers/md/raid5.c       |  254 +++++---
 drivers/md/raid5.h       |  150 ++++-
 3 files changed, 1703 insertions(+), 294 deletions(-)

--
2.9.3

[PATCH v4 1/8] md/r5cache: Check array size in r5l_init_log

[Song Liu]

Currently, r5l_write_stripe checks meta size for each stripe write,
which is not necessary.

With this patch, r5l_init_log checks maximal meta size of the array,
which is (r5l_meta_block + raid_disks x r5l_payload_data_parity).
If this is too big to fit in one page, r5l_init_log aborts.

With current meta data, r5l_log support raid_disks up to 203.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 drivers/md/raid5-cache.c | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 1b1ab4a..7557791b 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -441,7 +441,6 @@ int r5l_write_stripe(struct r5l_log *log, struct stripe_head *sh)
 {
 	int write_disks = 0;
 	int data_pages, parity_pages;
-	int meta_size;
 	int reserve;
 	int i;
 	int ret = 0;
@@ -473,15 +472,6 @@ int r5l_write_stripe(struct r5l_log *log, struct stripe_head *sh)
 	parity_pages = 1 + !!(sh->qd_idx >= 0);
 	data_pages = write_disks - parity_pages;
 
-	meta_size =
-		((sizeof(struct r5l_payload_data_parity) + sizeof(__le32))
-		 * data_pages) +
-		sizeof(struct r5l_payload_data_parity) +
-		sizeof(__le32) * parity_pages;
-	/* Doesn't work with very big raid array */
-	if (meta_size + sizeof(struct r5l_meta_block) > PAGE_SIZE)
-		return -EINVAL;
-
 	set_bit(STRIPE_LOG_TRAPPED, &sh->state);
 	/*
 	 * The stripe must enter state machine again to finish the write, so
@@ -1184,6 +1174,22 @@ int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
 
 	if (PAGE_SIZE != 4096)
 		return -EINVAL;
+
+	/*
+	 * The PAGE_SIZE must be big enough to hold 1 r5l_meta_block and
+	 * raid_disks r5l_payload_data_parity.
+	 *
+	 * Write journal and cache does not work for very big array
+	 * (raid_disks > 203)
+	 */
+	if (sizeof(struct r5l_meta_block) +
+	    ((sizeof(struct r5l_payload_data_parity) + sizeof(__le32)) *
+	     conf->raid_disks) > PAGE_SIZE) {
+		pr_err("md/raid:%s: write journal/cache doesn't work for array with %d disks\n",
+		       mdname(conf->mddev), conf->raid_disks);
+		return -EINVAL;
+	}
+
 	log = kzalloc(sizeof(*log), GFP_KERNEL);
 	if (!log)
 		return -ENOMEM;
-- 
2.9.3

[PATCH v4 2/8] md/r5cache: move some code to raid5.h

[Song Liu]

Move some define and inline functions to raid5.h, so they can be
used in raid5-cache.c

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 drivers/md/raid5.c | 71 -------------------------------------------------
 drivers/md/raid5.h | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 77 insertions(+), 71 deletions(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index f94472d..67d4f49 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -70,19 +70,6 @@ module_param(devices_handle_discard_safely, bool, 0644);
 MODULE_PARM_DESC(devices_handle_discard_safely,
 		 "Set to Y if all devices in each array reliably return zeroes on reads from discarded regions");
 static struct workqueue_struct *raid5_wq;
-/*
- * Stripe cache
- */
-
-#define NR_STRIPES		256
-#define STRIPE_SIZE		PAGE_SIZE
-#define STRIPE_SHIFT		(PAGE_SHIFT - 9)
-#define STRIPE_SECTORS		(STRIPE_SIZE>>9)
-#define	IO_THRESHOLD		1
-#define BYPASS_THRESHOLD	1
-#define NR_HASH			(PAGE_SIZE / sizeof(struct hlist_head))
-#define HASH_MASK		(NR_HASH - 1)
-#define MAX_STRIPE_BATCH	8
 
 static inline struct hlist_head *stripe_hash(struct r5conf *conf, sector_t sect)
 {
@@ -126,64 +113,6 @@ static inline void unlock_all_device_hash_locks_irq(struct r5conf *conf)
 	local_irq_enable();
 }
 
-/* bio's attached to a stripe+device for I/O are linked together in bi_sector
- * order without overlap.  There may be several bio's per stripe+device, and
- * a bio could span several devices.
- * When walking this list for a particular stripe+device, we must never proceed
- * beyond a bio that extends past this device, as the next bio might no longer
- * be valid.
- * This function is used to determine the 'next' bio in the list, given the sector
- * of the current stripe+device
- */
-static inline struct bio *r5_next_bio(struct bio *bio, sector_t sector)
-{
-	int sectors = bio_sectors(bio);
-	if (bio->bi_iter.bi_sector + sectors < sector + STRIPE_SECTORS)
-		return bio->bi_next;
-	else
-		return NULL;
-}
-
-/*
- * We maintain a biased count of active stripes in the bottom 16 bits of
- * bi_phys_segments, and a count of processed stripes in the upper 16 bits
- */
-static inline int raid5_bi_processed_stripes(struct bio *bio)
-{
-	atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
-	return (atomic_read(segments) >> 16) & 0xffff;
-}
-
-static inline int raid5_dec_bi_active_stripes(struct bio *bio)
-{
-	atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
-	return atomic_sub_return(1, segments) & 0xffff;
-}
-
-static inline void raid5_inc_bi_active_stripes(struct bio *bio)
-{
-	atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
-	atomic_inc(segments);
-}
-
-static inline void raid5_set_bi_processed_stripes(struct bio *bio,
-	unsigned int cnt)
-{
-	atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
-	int old, new;
-
-	do {
-		old = atomic_read(segments);
-		new = (old & 0xffff) | (cnt << 16);
-	} while (atomic_cmpxchg(segments, old, new) != old);
-}
-
-static inline void raid5_set_bi_stripes(struct bio *bio, unsigned int cnt)
-{
-	atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
-	atomic_set(segments, cnt);
-}
-
 /* Find first data disk in a raid6 stripe */
 static inline int raid6_d0(struct stripe_head *sh)
 {
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 517d4b6..46cfe93 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -410,6 +410,83 @@ struct disk_info {
 	struct md_rdev	*rdev, *replacement;
 };
 
+/*
+ * Stripe cache
+ */
+
+#define NR_STRIPES		256
+#define STRIPE_SIZE		PAGE_SIZE
+#define STRIPE_SHIFT		(PAGE_SHIFT - 9)
+#define STRIPE_SECTORS		(STRIPE_SIZE>>9)
+#define	IO_THRESHOLD		1
+#define BYPASS_THRESHOLD	1
+#define NR_HASH			(PAGE_SIZE / sizeof(struct hlist_head))
+#define HASH_MASK		(NR_HASH - 1)
+#define MAX_STRIPE_BATCH	8
+
+/* bio's attached to a stripe+device for I/O are linked together in bi_sector
+ * order without overlap.  There may be several bio's per stripe+device, and
+ * a bio could span several devices.
+ * When walking this list for a particular stripe+device, we must never proceed
+ * beyond a bio that extends past this device, as the next bio might no longer
+ * be valid.
+ * This function is used to determine the 'next' bio in the list, given the
+ * sector of the current stripe+device
+ */
+static inline struct bio *r5_next_bio(struct bio *bio, sector_t sector)
+{
+	int sectors = bio_sectors(bio);
+
+	if (bio->bi_iter.bi_sector + sectors < sector + STRIPE_SECTORS)
+		return bio->bi_next;
+	else
+		return NULL;
+}
+
+/*
+ * We maintain a biased count of active stripes in the bottom 16 bits of
+ * bi_phys_segments, and a count of processed stripes in the upper 16 bits
+ */
+static inline int raid5_bi_processed_stripes(struct bio *bio)
+{
+	atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
+
+	return (atomic_read(segments) >> 16) & 0xffff;
+}
+
+static inline int raid5_dec_bi_active_stripes(struct bio *bio)
+{
+	atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
+
+	return atomic_sub_return(1, segments) & 0xffff;
+}
+
+static inline void raid5_inc_bi_active_stripes(struct bio *bio)
+{
+	atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
+
+	atomic_inc(segments);
+}
+
+static inline void raid5_set_bi_processed_stripes(struct bio *bio,
+	unsigned int cnt)
+{
+	atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
+	int old, new;
+
+	do {
+		old = atomic_read(segments);
+		new = (old & 0xffff) | (cnt << 16);
+	} while (atomic_cmpxchg(segments, old, new) != old);
+}
+
+static inline void raid5_set_bi_stripes(struct bio *bio, unsigned int cnt)
+{
+	atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
+
+	atomic_set(segments, cnt);
+}
+
 /* NOTE NR_STRIPE_HASH_LOCKS must remain below 64.
  * This is because we sometimes take all the spinlocks
  * and creating that much locking depth can cause
-- 
2.9.3

[PATCH v4 3/8] md/r5cache: State machine for raid5-cache write back mode

[Song Liu]

The raid5-cache write back mode as 2 states for each stripe: write state
and reclaim state. This patch adds bare state machine for these two
states.

2 flags are added to sh->state for raid5-cache states:
 - STRIPE_R5C_FROZEN
 - STRIPE_R5C_WRITTEN

STRIPE_R5C_FROZEN is the key flag to differentiate write state
and reclaim state.

STRIPE_R5C_WRITTEN is a helper flag to bring the stripe back from
reclaim state back to write state.

In write through mode, every stripe also goes between write state
and reclaim state (in r5c_handle_stripe_dirtying() and
r5c_handle_stripe_written()).

Please note: this is a "no-op" patch for raid5-cache write through
mode.

The following detailed explanation is copied from the raid5-cache.c:

/*
 * raid5 cache state machine
 *
 * The RAID cache works in two major states for each stripe: write state
 * and reclaim state. These states are controlled by flags STRIPE_R5C_FROZEN
 * and STRIPE_R5C_WRITTEN
 *
 * STRIPE_R5C_FROZEN is the key flag to differentiate write state and reclaim
 * state. The write state runs w/ STRIPE_R5C_FROZEN == 0. While the reclaim
 * state runs w/ STRIPE_R5C_FROZEN == 1.
 *
 * STRIPE_R5C_WRITTEN is a helper flag to bring the stripe back from reclaim
 * state to write state. Specifically, STRIPE_R5C_WRITTEN triggers clean up
 * process in r5c_handle_stripe_written. STRIPE_R5C_WRITTEN is set when data
 * and parity of a stripe is all in journal device; and cleared when the data
 * and parity are all in RAID disks.
 *
 * The following is another way to show how STRIPE_R5C_FROZEN and
 * STRIPE_R5C_WRITTEN work:
 *
 * write state: STRIPE_R5C_FROZEN = 0 STRIPE_R5C_WRITTEN = 0
 * reclaim state: STRIPE_R5C_FROZEN = 1
 *
 * write => reclaim: set STRIPE_R5C_FROZEN in r5c_freeze_stripe_for_reclaim
 * reclaim => write:
 * 1. write parity to journal, when finished, set STRIPE_R5C_WRITTEN
 * 2. write data/parity to raid disks, when finished, clear both
 *    STRIPE_R5C_FROZEN and STRIPE_R5C_WRITTEN
 *
 * In write through mode (journal only) the stripe still goes through these
 * state change, except that STRIPE_R5C_FROZEN is set on write in
 * r5c_handle_stripe_dirtying().
 */

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 drivers/md/raid5-cache.c | 125 +++++++++++++++++++++++++++++++++++++++++++++--
 drivers/md/raid5.c       |  20 ++++++--
 drivers/md/raid5.h       |  10 +++-
 3 files changed, 148 insertions(+), 7 deletions(-)

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 7557791b..9e05850 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -40,6 +40,47 @@
  */
 #define R5L_POOL_SIZE	4
 
+enum r5c_state {
+	R5C_STATE_NO_CACHE = 0,
+	R5C_STATE_WRITE_THROUGH = 1,
+	R5C_STATE_WRITE_BACK = 2,
+	R5C_STATE_CACHE_BROKEN = 3,
+};
+
+/*
+ * raid5 cache state machine
+ *
+ * The RAID cache works in two major states for each stripe: write state and
+ * reclaim state. These states are controlled by flags STRIPE_R5C_FROZEN and
+ * STRIPE_R5C_WRITTEN
+ *
+ * STRIPE_R5C_FROZEN is the key flag to differentiate write state and reclaim
+ * state. The write state runs w/ STRIPE_R5C_FROZEN == 0. While the reclaim
+ * state runs w/ STRIPE_R5C_FROZEN == 1.
+ *
+ * STRIPE_R5C_WRITTEN is a helper flag to bring the stripe back from reclaim
+ * state to write state. Specifically, STRIPE_R5C_WRITTEN triggers clean up
+ * process in r5c_handle_stripe_written. STRIPE_R5C_WRITTEN is set when data
+ * and parity of a stripe is all in journal device; and cleared when the data
+ * and parity are all in RAID disks.
+ *
+ * The following is another way to show how STRIPE_R5C_FROZEN and
+ * STRIPE_R5C_WRITTEN work:
+ *
+ * write state: STRIPE_R5C_FROZEN = 0 STRIPE_R5C_WRITTEN = 0
+ * reclaim state: STRIPE_R5C_FROZEN = 1
+ *
+ * write => reclaim: set STRIPE_R5C_FROZEN in r5c_freeze_stripe_for_reclaim
+ * reclaim => write:
+ * 1. write parity to journal, when finished, set STRIPE_R5C_WRITTEN
+ * 2. write data/parity to raid disks, when finished, clear both
+ *    STRIPE_R5C_FROZEN and STRIPE_R5C_WRITTEN
+ *
+ * In write through mode (journal only) the stripe also goes through these
+ * state change, except that STRIPE_R5C_FROZEN is set on write in
+ * r5c_handle_stripe_dirtying().
+ */
+
 struct r5l_log {
 	struct md_rdev *rdev;
 
@@ -96,6 +137,9 @@ struct r5l_log {
 	spinlock_t no_space_stripes_lock;
 
 	bool need_cache_flush;
+
+	/* for r5c_cache */
+	enum r5c_state r5c_state;
 };
 
 /*
@@ -133,6 +177,11 @@ enum r5l_io_unit_state {
 	IO_UNIT_STRIPE_END = 3,	/* stripes data finished writing to raid */
 };
 
+bool r5c_is_writeback(struct r5l_log *log)
+{
+	return (log != NULL && log->r5c_state == R5C_STATE_WRITE_BACK);
+}
+
 static sector_t r5l_ring_add(struct r5l_log *log, sector_t start, sector_t inc)
 {
 	start += inc;
@@ -168,12 +217,44 @@ static void __r5l_set_io_unit_state(struct r5l_io_unit *io,
 	io->state = state;
 }
 
+/*
+ * Freeze the stripe, thus send the stripe into reclaim path.
+ *
+ * In current implementation, STRIPE_R5C_FROZEN is also set in write through
+ * mode (in r5c_handle_stripe_dirtying). This does not change the behavior of
+ * for write through mode.
+ */
+void r5c_freeze_stripe_for_reclaim(struct stripe_head *sh)
+{
+	struct r5conf *conf = sh->raid_conf;
+	struct r5l_log *log = conf->log;
+
+	if (!log)
+		return;
+	WARN_ON(test_bit(STRIPE_R5C_FROZEN, &sh->state));
+	set_bit(STRIPE_R5C_FROZEN, &sh->state);
+}
+
+static void r5c_finish_cache_stripe(struct stripe_head *sh)
+{
+	struct r5l_log *log = sh->raid_conf->log;
+
+	if (log->r5c_state == R5C_STATE_WRITE_THROUGH) {
+		BUG_ON(!test_bit(STRIPE_R5C_FROZEN, &sh->state));
+		set_bit(STRIPE_R5C_WRITTEN, &sh->state);
+	} else
+		BUG(); /* write back logic in next patch */
+}
+
 static void r5l_io_run_stripes(struct r5l_io_unit *io)
 {
 	struct stripe_head *sh, *next;
 
 	list_for_each_entry_safe(sh, next, &io->stripe_list, log_list) {
 		list_del_init(&sh->log_list);
+
+		r5c_finish_cache_stripe(sh);
+
 		set_bit(STRIPE_HANDLE, &sh->state);
 		raid5_release_stripe(sh);
 	}
@@ -412,18 +493,19 @@ static int r5l_log_stripe(struct r5l_log *log, struct stripe_head *sh,
 		r5l_append_payload_page(log, sh->dev[i].page);
 	}
 
-	if (sh->qd_idx >= 0) {
+	if (parity_pages == 2) {
 		r5l_append_payload_meta(log, R5LOG_PAYLOAD_PARITY,
 					sh->sector, sh->dev[sh->pd_idx].log_checksum,
 					sh->dev[sh->qd_idx].log_checksum, true);
 		r5l_append_payload_page(log, sh->dev[sh->pd_idx].page);
 		r5l_append_payload_page(log, sh->dev[sh->qd_idx].page);
-	} else {
+	} else if (parity_pages == 1) {
 		r5l_append_payload_meta(log, R5LOG_PAYLOAD_PARITY,
 					sh->sector, sh->dev[sh->pd_idx].log_checksum,
 					0, false);
 		r5l_append_payload_page(log, sh->dev[sh->pd_idx].page);
-	}
+	} else
+		BUG_ON(parity_pages != 0);
 
 	list_add_tail(&sh->log_list, &io->stripe_list);
 	atomic_inc(&io->pending_stripe);
@@ -455,6 +537,8 @@ int r5l_write_stripe(struct r5l_log *log, struct stripe_head *sh)
 		return -EAGAIN;
 	}
 
+	WARN_ON(!test_bit(STRIPE_R5C_FROZEN, &sh->state));
+
 	for (i = 0; i < sh->disks; i++) {
 		void *addr;
 
@@ -1101,6 +1185,39 @@ static void r5l_write_super(struct r5l_log *log, sector_t cp)
 	set_bit(MD_CHANGE_DEVS, &mddev->flags);
 }
 
+int r5c_handle_stripe_dirtying(struct r5conf *conf,
+			       struct stripe_head *sh,
+			       struct stripe_head_state *s,
+			       int disks)
+{
+	struct r5l_log *log = conf->log;
+
+	if (!log || test_bit(STRIPE_R5C_FROZEN, &sh->state))
+		return -EAGAIN;
+
+	if (conf->log->r5c_state == R5C_STATE_WRITE_THROUGH ||
+	    conf->mddev->degraded != 0) {
+		/* write through mode */
+		r5c_freeze_stripe_for_reclaim(sh);
+		return -EAGAIN;
+	}
+	BUG();  /* write back logic in next commit */
+	return 0;
+}
+
+/*
+ * clean up the stripe (clear STRIPE_R5C_FROZEN etc.) after the stripe is
+ * committed to RAID disks
+*/
+void r5c_handle_stripe_written(struct r5conf *conf,
+			       struct stripe_head *sh)
+{
+	if (!test_and_clear_bit(STRIPE_R5C_WRITTEN, &sh->state))
+		return;
+	WARN_ON(!test_bit(STRIPE_R5C_FROZEN, &sh->state));
+	clear_bit(STRIPE_R5C_FROZEN, &sh->state);
+}
+
 static int r5l_load_log(struct r5l_log *log)
 {
 	struct md_rdev *rdev = log->rdev;
@@ -1236,6 +1353,8 @@ int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
 	INIT_LIST_HEAD(&log->no_space_stripes);
 	spin_lock_init(&log->no_space_stripes_lock);
 
+	log->r5c_state = R5C_STATE_WRITE_THROUGH;
+
 	if (r5l_load_log(log))
 		goto error;
 
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 67d4f49..2e3e61a 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3506,6 +3506,9 @@ static void handle_stripe_dirtying(struct r5conf *conf,
 	int rmw = 0, rcw = 0, i;
 	sector_t recovery_cp = conf->mddev->recovery_cp;
 
+	if (r5c_handle_stripe_dirtying(conf, sh, s, disks) == 0)
+		return;
+
 	/* Check whether resync is now happening or should start.
 	 * If yes, then the array is dirty (after unclean shutdown or
 	 * initial creation), so parity in some stripes might be inconsistent.
@@ -4396,13 +4399,23 @@ static void handle_stripe(struct stripe_head *sh)
 	    || s.expanding)
 		handle_stripe_fill(sh, &s, disks);
 
-	/* Now to consider new write requests and what else, if anything
-	 * should be read.  We do not handle new writes when:
+	/*
+	 * When the stripe finishes full journal write cycle (write to journal
+	 * and raid disk), this is the clean up procedure so it is ready for
+	 * next operation.
+	 */
+	r5c_handle_stripe_written(conf, sh);
+
+	/*
+	 * Now to consider new write requests, cache write back and what else,
+	 * if anything should be read.  We do not handle new writes when:
 	 * 1/ A 'write' operation (copy+xor) is already in flight.
 	 * 2/ A 'check' operation is in flight, as it may clobber the parity
 	 *    block.
+	 * 3/ A r5c cache log write is in flight.
 	 */
-	if (s.to_write && !sh->reconstruct_state && !sh->check_state)
+	if ((s.to_write || test_bit(STRIPE_R5C_FROZEN, &sh->state)) &&
+	    !sh->reconstruct_state && !sh->check_state && !sh->log_io)
 		handle_stripe_dirtying(conf, sh, &s, disks);
 
 	/* maybe we need to check and possibly fix the parity for this stripe
@@ -5122,6 +5135,7 @@ 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)
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 46cfe93..8bae64b 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -345,7 +345,9 @@ enum {
 	STRIPE_BITMAP_PENDING,	/* Being added to bitmap, don't add
 				 * to batch yet.
 				 */
-	STRIPE_LOG_TRAPPED, /* trapped into log */
+	STRIPE_LOG_TRAPPED,	/* trapped into log */
+	STRIPE_R5C_FROZEN,	/* r5c_cache frozen and being written out */
+	STRIPE_R5C_WRITTEN,	/* ready for r5c_handle_stripe_written() */
 };
 
 #define STRIPE_EXPAND_SYNC_FLAGS \
@@ -712,4 +714,10 @@ extern void r5l_stripe_write_finished(struct stripe_head *sh);
 extern int r5l_handle_flush_request(struct r5l_log *log, struct bio *bio);
 extern void r5l_quiesce(struct r5l_log *log, int state);
 extern bool r5l_log_disk_error(struct r5conf *conf);
+extern bool r5c_is_writeback(struct r5l_log *log);
+extern int
+r5c_handle_stripe_dirtying(struct r5conf *conf, struct stripe_head *sh,
+			   struct stripe_head_state *s, int disks);
+extern void
+r5c_handle_stripe_written(struct r5conf *conf, struct stripe_head *sh);
 #endif
-- 
2.9.3

[PATCH v4 4/8] md/r5cache: write part of r5cache

[Song Liu]

This is the write part of r5cache. The cache is integrated with
stripe cache of raid456. It leverages code of r5l_log to write
data to journal device.

r5cache split current write path into 2 parts: the write path
and the reclaim path. The write path is as following:
1. write data to journal
   (r5c_handle_stripe_dirtying, r5c_cache_data)
2. call bio_endio
   (r5c_handle_data_cached, r5c_return_dev_pending_writes).

Then the reclaim path is as:
1. Freeze the stripe (r5c_freeze_stripe_for_reclaim)
2. Calcualte parity (reconstruct or RMW)
3. Write parity (and maybe some other data) to journal device
4. Write data and parity to RAID disks

Reclaim path of the cache is implemented in the next patch.

With r5cache, write operation does not wait for parity calculation
and write out, so the write latency is lower (1 write to journal
device vs. read and then write to raid disks). Also, r5cache will
reduce RAID overhead (multipile IO due to read-modify-write of
parity) and provide more opportunities of full stripe writes.

This patch adds 2 flags to stripe_head.state:
 - STRIPE_R5C_PARTIAL_STRIPE,
 - STRIPE_R5C_FULL_STRIPE,

Instead of inactive_list, stripes with cached data are tracked in
r5conf->r5c_full_stripe_list and r5conf->r5c_partial_stripe_list.
STRIPE_R5C_FULL_STRIPE and STRIPE_R5C_PARTIAL_STRIPE are flags for
stripes in these lists. Note: stripes in r5c_full/partial_stripe_list
are not considered as "active".

For RMW, the code allocates an extra page for each data block
being updated.  This is stored in r5dev->page and the old data
is read into it.  Then the prexor calculation subtracts ->page
from the parity block, and the reconstruct calculation adds the
->orig_page data back into the parity block.

r5cache naturally excludes SkipCopy. With R5_Wantcache bit set,
async_copy_data will not skip copy.

There are some known limitations of the cache implementation:

1. Write cache only covers full page writes (R5_OVERWRITE). Writes
   of smaller granularity are write through.
2. Only one log io (sh->log_io) for each stripe at anytime. Later
   writes for the same stripe have to wait. This can be improved by
   moving log_io to r5dev.
3. With writeback cache, read path must enter state machine, which
   is a significant bottleneck for some workloads.
4. There is no per stripe checkpoint (with r5l_payload_flush) in
   the log, so recovery code has to replay more than necessary data
   (sometimes all the log from last_checkpoint). This reduces
   availability of the array.

This patch includes a fix proposed by ZhengYuan Liu
<liuzhengyuan@kylinos.cn>

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 drivers/md/raid5-cache.c | 204 +++++++++++++++++++++++++++++++++++++++++++++--
 drivers/md/raid5.c       | 137 ++++++++++++++++++++++++++-----
 drivers/md/raid5.h       |  22 +++++
 3 files changed, 336 insertions(+), 27 deletions(-)

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 9e05850..92d3d7b 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -20,6 +20,7 @@
 #include <linux/random.h>
 #include "md.h"
 #include "raid5.h"
+#include "bitmap.h"
 
 /*
  * metadata/data stored in disk with 4k size unit (a block) regardless
@@ -217,6 +218,44 @@ static void __r5l_set_io_unit_state(struct r5l_io_unit *io,
 	io->state = state;
 }
 
+static void
+r5c_return_dev_pending_writes(struct r5conf *conf, struct r5dev *dev,
+			      struct bio_list *return_bi)
+{
+	struct bio *wbi, *wbi2;
+
+	wbi = dev->written;
+	dev->written = NULL;
+	while (wbi && wbi->bi_iter.bi_sector <
+	       dev->sector + STRIPE_SECTORS) {
+		wbi2 = r5_next_bio(wbi, dev->sector);
+		if (!raid5_dec_bi_active_stripes(wbi)) {
+			md_write_end(conf->mddev);
+			bio_list_add(return_bi, wbi);
+		}
+		wbi = wbi2;
+	}
+}
+
+void r5c_handle_cached_data_endio(struct r5conf *conf,
+	  struct stripe_head *sh, int disks, struct bio_list *return_bi)
+{
+	int i;
+
+	for (i = sh->disks; i--; ) {
+		if (test_bit(R5_InCache, &sh->dev[i].flags) &&
+		    sh->dev[i].written) {
+			set_bit(R5_UPTODATE, &sh->dev[i].flags);
+			r5c_return_dev_pending_writes(conf, &sh->dev[i],
+						      return_bi);
+			bitmap_endwrite(conf->mddev->bitmap, sh->sector,
+					STRIPE_SECTORS,
+					!test_bit(STRIPE_DEGRADED, &sh->state),
+					0);
+		}
+	}
+}
+
 /*
  * Freeze the stripe, thus send the stripe into reclaim path.
  *
@@ -233,6 +272,48 @@ void r5c_freeze_stripe_for_reclaim(struct stripe_head *sh)
 		return;
 	WARN_ON(test_bit(STRIPE_R5C_FROZEN, &sh->state));
 	set_bit(STRIPE_R5C_FROZEN, &sh->state);
+
+	if (log->r5c_state == R5C_STATE_WRITE_THROUGH)
+		return;
+
+	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)
+{
+	int i;
+
+	for (i = sh->disks; i--; )
+		if (test_and_clear_bit(R5_Wantcache, &sh->dev[i].flags)) {
+			set_bit(R5_InCache, &sh->dev[i].flags);
+			clear_bit(R5_LOCKED, &sh->dev[i].flags);
+			atomic_inc(&sh->dev_in_cache);
+		}
+}
+
+/*
+ * this journal write must contain full parity,
+ * it may also contain some data pages
+ */
+static void r5c_handle_parity_cached(struct stripe_head *sh)
+{
+	int i;
+
+	for (i = sh->disks; i--; )
+		if (test_bit(R5_InCache, &sh->dev[i].flags))
+			set_bit(R5_Wantwrite, &sh->dev[i].flags);
+	set_bit(STRIPE_R5C_WRITTEN, &sh->state);
 }
 
 static void r5c_finish_cache_stripe(struct stripe_head *sh)
@@ -242,8 +323,10 @@ static void r5c_finish_cache_stripe(struct stripe_head *sh)
 	if (log->r5c_state == R5C_STATE_WRITE_THROUGH) {
 		BUG_ON(!test_bit(STRIPE_R5C_FROZEN, &sh->state));
 		set_bit(STRIPE_R5C_WRITTEN, &sh->state);
-	} else
-		BUG(); /* write back logic in next patch */
+	} else if (test_bit(STRIPE_R5C_FROZEN, &sh->state))
+		r5c_handle_parity_cached(sh);
+	else
+		r5c_handle_data_cached(sh);
 }
 
 static void r5l_io_run_stripes(struct r5l_io_unit *io)
@@ -483,7 +566,8 @@ static int r5l_log_stripe(struct r5l_log *log, struct stripe_head *sh,
 	io = log->current_io;
 
 	for (i = 0; i < sh->disks; i++) {
-		if (!test_bit(R5_Wantwrite, &sh->dev[i].flags))
+		if (!test_bit(R5_Wantwrite, &sh->dev[i].flags) &&
+		    !test_bit(R5_Wantcache, &sh->dev[i].flags))
 			continue;
 		if (i == sh->pd_idx || i == sh->qd_idx)
 			continue;
@@ -514,7 +598,6 @@ static int r5l_log_stripe(struct r5l_log *log, struct stripe_head *sh,
 	return 0;
 }
 
-static void r5l_wake_reclaim(struct r5l_log *log, sector_t space);
 /*
  * running in raid5d, where reclaim could wait for raid5d too (when it flushes
  * data from log to raid disks), so we shouldn't wait for reclaim here
@@ -544,6 +627,10 @@ int r5l_write_stripe(struct r5l_log *log, struct stripe_head *sh)
 
 		if (!test_bit(R5_Wantwrite, &sh->dev[i].flags))
 			continue;
+
+		if (test_bit(R5_InCache, &sh->dev[i].flags))
+			continue;
+
 		write_disks++;
 		/* checksum is already calculated in last run */
 		if (test_bit(STRIPE_LOG_TRAPPED, &sh->state))
@@ -809,7 +896,6 @@ static void r5l_write_super_and_discard_space(struct r5l_log *log,
 	}
 }
 
-
 static void r5l_do_reclaim(struct r5l_log *log)
 {
 	sector_t reclaim_target = xchg(&log->reclaim_target, 0);
@@ -872,7 +958,7 @@ static void r5l_reclaim_thread(struct md_thread *thread)
 	r5l_do_reclaim(log);
 }
 
-static void r5l_wake_reclaim(struct r5l_log *log, sector_t space)
+void r5l_wake_reclaim(struct r5l_log *log, sector_t space)
 {
 	unsigned long target;
 	unsigned long new = (unsigned long)space; /* overflow in theory */
@@ -1191,6 +1277,8 @@ int r5c_handle_stripe_dirtying(struct r5conf *conf,
 			       int disks)
 {
 	struct r5l_log *log = conf->log;
+	int i;
+	struct r5dev *dev;
 
 	if (!log || test_bit(STRIPE_R5C_FROZEN, &sh->state))
 		return -EAGAIN;
@@ -1201,21 +1289,121 @@ int r5c_handle_stripe_dirtying(struct r5conf *conf,
 		r5c_freeze_stripe_for_reclaim(sh);
 		return -EAGAIN;
 	}
-	BUG();  /* write back logic in next commit */
+
+	s->to_cache = 0;
+
+	for (i = disks; i--; ) {
+		dev = &sh->dev[i];
+		/* if none-overwrite, use the reclaim path (write through) */
+		if (dev->towrite && !test_bit(R5_OVERWRITE, &dev->flags) &&
+		    !test_bit(R5_InCache, &dev->flags)) {
+			r5c_freeze_stripe_for_reclaim(sh);
+			return -EAGAIN;
+		}
+	}
+
+	for (i = disks; i--; ) {
+		dev = &sh->dev[i];
+		if (dev->towrite) {
+			set_bit(R5_Wantcache, &dev->flags);
+			set_bit(R5_Wantdrain, &dev->flags);
+			set_bit(R5_LOCKED, &dev->flags);
+			s->to_cache++;
+		}
+	}
+
+	if (s->to_cache)
+		set_bit(STRIPE_OP_BIODRAIN, &s->ops_request);
+
 	return 0;
 }
 
 /*
  * clean up the stripe (clear STRIPE_R5C_FROZEN etc.) after the stripe is
  * committed to RAID disks
-*/
+ */
 void r5c_handle_stripe_written(struct r5conf *conf,
 			       struct stripe_head *sh)
 {
+	int i;
+	int do_wakeup = 0;
+
 	if (!test_and_clear_bit(STRIPE_R5C_WRITTEN, &sh->state))
 		return;
 	WARN_ON(!test_bit(STRIPE_R5C_FROZEN, &sh->state));
 	clear_bit(STRIPE_R5C_FROZEN, &sh->state);
+
+	if (conf->log->r5c_state == R5C_STATE_WRITE_THROUGH)
+		return;
+
+	for (i = sh->disks; i--; ) {
+		if (test_and_clear_bit(R5_InCache, &sh->dev[i].flags))
+			atomic_dec(&sh->dev_in_cache);
+		if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
+			do_wakeup = 1;
+	}
+
+	if (test_and_clear_bit(STRIPE_FULL_WRITE, &sh->state))
+		if (atomic_dec_and_test(&conf->pending_full_writes))
+			md_wakeup_thread(conf->mddev->thread);
+
+	if (do_wakeup)
+		wake_up(&conf->wait_for_overlap);
+}
+
+int
+r5c_cache_data(struct r5l_log *log, struct stripe_head *sh,
+	       struct stripe_head_state *s)
+{
+	int pages;
+	int reserve;
+	int i;
+	int ret = 0;
+	int page_count = 0;
+
+	BUG_ON(!log);
+
+	for (i = 0; i < sh->disks; i++) {
+		void *addr;
+
+		if (!test_bit(R5_Wantcache, &sh->dev[i].flags))
+			continue;
+		addr = kmap_atomic(sh->dev[i].page);
+		sh->dev[i].log_checksum = crc32c_le(log->uuid_checksum,
+						    addr, PAGE_SIZE);
+		kunmap_atomic(addr);
+		page_count++;
+	}
+	WARN_ON(page_count != s->to_cache);
+	pages = s->to_cache;
+
+	/*
+	 * The stripe must enter state machine again to call endio, so
+	 * don't delay.
+	 */
+	clear_bit(STRIPE_DELAYED, &sh->state);
+	atomic_inc(&sh->count);
+
+	mutex_lock(&log->io_mutex);
+	/* meta + data */
+	reserve = (1 + pages) << (PAGE_SHIFT - 9);
+	if (!r5l_has_free_space(log, reserve)) {
+		spin_lock(&log->no_space_stripes_lock);
+		list_add_tail(&sh->log_list, &log->no_space_stripes);
+		spin_unlock(&log->no_space_stripes_lock);
+
+		r5l_wake_reclaim(log, reserve);
+	} else {
+		ret = r5l_log_stripe(log, sh, pages, 0);
+		if (ret) {
+			spin_lock_irq(&log->io_list_lock);
+			list_add_tail(&sh->log_list, &log->no_mem_stripes);
+			spin_unlock_irq(&log->io_list_lock);
+		}
+	}
+
+	mutex_unlock(&log->io_mutex);
+	return 0;
 }
 
 static int r5l_load_log(struct r5l_log *log)
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 2e3e61a..27fd183 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -245,8 +245,25 @@ static void do_release_stripe(struct r5conf *conf, struct stripe_head *sh,
 			    < IO_THRESHOLD)
 				md_wakeup_thread(conf->mddev->thread);
 		atomic_dec(&conf->active_stripes);
-		if (!test_bit(STRIPE_EXPANDING, &sh->state))
-			list_add_tail(&sh->lru, temp_inactive_list);
+		if (!test_bit(STRIPE_EXPANDING, &sh->state)) {
+			if (atomic_read(&sh->dev_in_cache) == 0) {
+				list_add_tail(&sh->lru, temp_inactive_list);
+			} else if (atomic_read(&sh->dev_in_cache) ==
+				   conf->raid_disks - conf->max_degraded) {
+				/* full stripe */
+				if (!test_and_set_bit(STRIPE_R5C_FULL_STRIPE, &sh->state))
+					atomic_inc(&conf->r5c_cached_full_stripes);
+				if (test_and_clear_bit(STRIPE_R5C_PARTIAL_STRIPE, &sh->state))
+					atomic_dec(&conf->r5c_cached_partial_stripes);
+				list_add_tail(&sh->lru, &conf->r5c_full_stripe_list);
+			} else {
+				/* partial stripe */
+				if (!test_and_set_bit(STRIPE_R5C_PARTIAL_STRIPE,
+						      &sh->state))
+					atomic_inc(&conf->r5c_cached_partial_stripes);
+				list_add_tail(&sh->lru, &conf->r5c_partial_stripe_list);
+			}
+		}
 	}
 }
 
@@ -830,6 +847,11 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
 
 	might_sleep();
 
+	if (s->to_cache) {
+		r5c_cache_data(conf->log, sh, s);
+		return;
+	}
+
 	if (r5l_write_stripe(conf->log, sh) == 0)
 		return;
 	for (i = disks; i--; ) {
@@ -1044,7 +1066,7 @@ again:
 static struct dma_async_tx_descriptor *
 async_copy_data(int frombio, struct bio *bio, struct page **page,
 	sector_t sector, struct dma_async_tx_descriptor *tx,
-	struct stripe_head *sh)
+	struct stripe_head *sh, int no_skipcopy)
 {
 	struct bio_vec bvl;
 	struct bvec_iter iter;
@@ -1084,7 +1106,8 @@ async_copy_data(int frombio, struct bio *bio, struct page **page,
 			if (frombio) {
 				if (sh->raid_conf->skip_copy &&
 				    b_offset == 0 && page_offset == 0 &&
-				    clen == STRIPE_SIZE)
+				    clen == STRIPE_SIZE &&
+				    !no_skipcopy)
 					*page = bio_page;
 				else
 					tx = async_memcpy(*page, bio_page, page_offset,
@@ -1166,7 +1189,7 @@ static void ops_run_biofill(struct stripe_head *sh)
 			while (rbi && rbi->bi_iter.bi_sector <
 				dev->sector + STRIPE_SECTORS) {
 				tx = async_copy_data(0, rbi, &dev->page,
-					dev->sector, tx, sh);
+						     dev->sector, tx, sh, 0);
 				rbi = r5_next_bio(rbi, dev->sector);
 			}
 		}
@@ -1293,7 +1316,8 @@ static int set_syndrome_sources(struct page **srcs,
 		if (i == sh->qd_idx || i == sh->pd_idx ||
 		    (srctype == SYNDROME_SRC_ALL) ||
 		    (srctype == SYNDROME_SRC_WANT_DRAIN &&
-		     test_bit(R5_Wantdrain, &dev->flags)) ||
+		     (test_bit(R5_Wantdrain, &dev->flags) ||
+		      test_bit(R5_InCache, &dev->flags))) ||
 		    (srctype == SYNDROME_SRC_WRITTEN &&
 		     dev->written))
 			srcs[slot] = sh->dev[i].page;
@@ -1472,9 +1496,25 @@ ops_run_compute6_2(struct stripe_head *sh, struct raid5_percpu *percpu)
 static void ops_complete_prexor(void *stripe_head_ref)
 {
 	struct stripe_head *sh = stripe_head_ref;
+	int i;
 
 	pr_debug("%s: stripe %llu\n", __func__,
 		(unsigned long long)sh->sector);
+
+	if (!r5c_is_writeback(sh->raid_conf->log))
+		return;
+
+	/*
+	 * raid5-cache write back uses orig_page during prexor. after prexor,
+	 * it is time to free orig_page
+	 */
+	for (i = sh->disks; i--; )
+		if (sh->dev[i].page != sh->dev[i].orig_page) {
+			struct page *p = sh->dev[i].page;
+
+			sh->dev[i].page = sh->dev[i].orig_page;
+			put_page(p);
+		}
 }
 
 static struct dma_async_tx_descriptor *
@@ -1496,7 +1536,8 @@ ops_run_prexor5(struct stripe_head *sh, struct raid5_percpu *percpu,
 	for (i = disks; i--; ) {
 		struct r5dev *dev = &sh->dev[i];
 		/* Only process blocks that are known to be uptodate */
-		if (test_bit(R5_Wantdrain, &dev->flags))
+		if (test_bit(R5_Wantdrain, &dev->flags) ||
+		    test_bit(R5_InCache, &dev->flags))
 			xor_srcs[count++] = dev->page;
 	}
 
@@ -1547,6 +1588,10 @@ ops_run_biodrain(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
 
 again:
 			dev = &sh->dev[i];
+			if (test_and_clear_bit(R5_InCache, &dev->flags)) {
+				BUG_ON(atomic_read(&sh->dev_in_cache) == 0);
+				atomic_dec(&sh->dev_in_cache);
+			}
 			spin_lock_irq(&sh->stripe_lock);
 			chosen = dev->towrite;
 			dev->towrite = NULL;
@@ -1554,7 +1599,13 @@ again:
 			BUG_ON(dev->written);
 			wbi = dev->written = chosen;
 			spin_unlock_irq(&sh->stripe_lock);
-			WARN_ON(dev->page != dev->orig_page);
+
+			/*
+			 * in biodrain stage, prexor for data in raid5-cache
+			 * is the only case where page != orig_page
+			 */
+			if (!test_bit(R5_Wantcache, &dev->flags))
+				WARN_ON(dev->page != dev->orig_page);
 
 			while (wbi && wbi->bi_iter.bi_sector <
 				dev->sector + STRIPE_SECTORS) {
@@ -1566,8 +1617,10 @@ again:
 					set_bit(R5_Discard, &dev->flags);
 				else {
 					tx = async_copy_data(1, wbi, &dev->page,
-						dev->sector, tx, sh);
-					if (dev->page != dev->orig_page) {
+							     dev->sector, tx, sh,
+							     test_bit(R5_Wantcache, &dev->flags));
+					if (dev->page != dev->orig_page &&
+					    !test_bit(R5_Wantcache, &dev->flags)) {
 						set_bit(R5_SkipCopy, &dev->flags);
 						clear_bit(R5_UPTODATE, &dev->flags);
 						clear_bit(R5_OVERWRITE, &dev->flags);
@@ -1675,7 +1728,8 @@ again:
 		xor_dest = xor_srcs[count++] = sh->dev[pd_idx].page;
 		for (i = disks; i--; ) {
 			struct r5dev *dev = &sh->dev[i];
-			if (head_sh->dev[i].written)
+			if (head_sh->dev[i].written ||
+			    test_bit(R5_InCache, &head_sh->dev[i].flags))
 				xor_srcs[count++] = dev->page;
 		}
 	} else {
@@ -1930,6 +1984,7 @@ static struct stripe_head *alloc_stripe(struct kmem_cache *sc, gfp_t gfp,
 		INIT_LIST_HEAD(&sh->batch_list);
 		INIT_LIST_HEAD(&sh->lru);
 		atomic_set(&sh->count, 1);
+		atomic_set(&sh->dev_in_cache, 0);
 		for (i = 0; i < disks; i++) {
 			struct r5dev *dev = &sh->dev[i];
 
@@ -2816,6 +2871,9 @@ schedule_reconstruction(struct stripe_head *sh, struct stripe_head_state *s,
 				if (!expand)
 					clear_bit(R5_UPTODATE, &dev->flags);
 				s->locked++;
+			} else if (test_bit(R5_InCache, &dev->flags)) {
+				set_bit(R5_LOCKED, &dev->flags);
+				s->locked++;
 			}
 		}
 		/* if we are not expanding this is a proper write request, and
@@ -2855,6 +2913,9 @@ schedule_reconstruction(struct stripe_head *sh, struct stripe_head_state *s,
 				set_bit(R5_LOCKED, &dev->flags);
 				clear_bit(R5_UPTODATE, &dev->flags);
 				s->locked++;
+			} else if (test_bit(R5_InCache, &dev->flags)) {
+				set_bit(R5_LOCKED, &dev->flags);
+				s->locked++;
 			}
 		}
 		if (!s->locked)
@@ -3529,9 +3590,12 @@ static void 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 || i == sh->pd_idx || i == sh->qd_idx) &&
+		if ((dev->towrite || i == sh->pd_idx || i == sh->qd_idx ||
+		     test_bit(R5_InCache, &dev->flags)) &&
 		    !test_bit(R5_LOCKED, &dev->flags) &&
-		    !(test_bit(R5_UPTODATE, &dev->flags) ||
+		    !((test_bit(R5_UPTODATE, &dev->flags) &&
+		       (!test_bit(R5_InCache, &dev->flags) ||
+			dev->page != dev->orig_page)) ||
 		      test_bit(R5_Wantcompute, &dev->flags))) {
 			if (test_bit(R5_Insync, &dev->flags))
 				rmw++;
@@ -3543,13 +3607,15 @@ static void handle_stripe_dirtying(struct r5conf *conf,
 		    i != sh->pd_idx && i != sh->qd_idx &&
 		    !test_bit(R5_LOCKED, &dev->flags) &&
 		    !(test_bit(R5_UPTODATE, &dev->flags) ||
-		    test_bit(R5_Wantcompute, &dev->flags))) {
+		      test_bit(R5_InCache, &dev->flags) ||
+		      test_bit(R5_Wantcompute, &dev->flags))) {
 			if (test_bit(R5_Insync, &dev->flags))
 				rcw++;
 			else
 				rcw += 2*disks;
 		}
 	}
+
 	pr_debug("for sector %llu, rmw=%d rcw=%d\n",
 		(unsigned long long)sh->sector, rmw, rcw);
 	set_bit(STRIPE_HANDLE, &sh->state);
@@ -3561,10 +3627,18 @@ static void handle_stripe_dirtying(struct r5conf *conf,
 					  (unsigned long long)sh->sector, rmw);
 		for (i = disks; i--; ) {
 			struct r5dev *dev = &sh->dev[i];
-			if ((dev->towrite || i == sh->pd_idx || i == sh->qd_idx) &&
+			if (test_bit(R5_InCache, &dev->flags) &&
+			    dev->page == dev->orig_page)
+				dev->page = alloc_page(GFP_NOIO);  /* prexor */
+
+			if ((dev->towrite ||
+			     i == sh->pd_idx || i == sh->qd_idx ||
+			     test_bit(R5_InCache, &dev->flags)) &&
 			    !test_bit(R5_LOCKED, &dev->flags) &&
-			    !(test_bit(R5_UPTODATE, &dev->flags) ||
-			    test_bit(R5_Wantcompute, &dev->flags)) &&
+			    !((test_bit(R5_UPTODATE, &dev->flags) &&
+			       (!test_bit(R5_InCache, &dev->flags) ||
+				dev->page != dev->orig_page)) ||
+			      test_bit(R5_Wantcompute, &dev->flags)) &&
 			    test_bit(R5_Insync, &dev->flags)) {
 				if (test_bit(STRIPE_PREREAD_ACTIVE,
 					     &sh->state)) {
@@ -3590,6 +3664,7 @@ static void handle_stripe_dirtying(struct r5conf *conf,
 			    i != sh->pd_idx && i != sh->qd_idx &&
 			    !test_bit(R5_LOCKED, &dev->flags) &&
 			    !(test_bit(R5_UPTODATE, &dev->flags) ||
+			      test_bit(R5_InCache, &dev->flags) ||
 			      test_bit(R5_Wantcompute, &dev->flags))) {
 				rcw++;
 				if (test_bit(R5_Insync, &dev->flags) &&
@@ -3629,7 +3704,7 @@ static void handle_stripe_dirtying(struct r5conf *conf,
 	 */
 	if ((s->req_compute || !test_bit(STRIPE_COMPUTE_RUN, &sh->state)) &&
 	    (s->locked == 0 && (rcw == 0 || rmw == 0) &&
-	    !test_bit(STRIPE_BIT_DELAY, &sh->state)))
+	     !test_bit(STRIPE_BIT_DELAY, &sh->state)))
 		schedule_reconstruction(sh, s, rcw == 0, 0);
 }
 
@@ -4120,6 +4195,10 @@ static void analyse_stripe(struct stripe_head *sh, struct stripe_head_state *s)
 			if (rdev && !test_bit(Faulty, &rdev->flags))
 				do_recovery = 1;
 		}
+		if (test_bit(R5_InCache, &dev->flags) && dev->written)
+			s->just_cached++;
+		if (test_bit(R5_Wantcache, &dev->flags) && dev->written)
+			s->want_cache++;
 	}
 	if (test_bit(STRIPE_SYNCING, &sh->state)) {
 		/* If there is a failed device being replaced,
@@ -4285,6 +4364,17 @@ static void handle_stripe(struct stripe_head *sh)
 
 	analyse_stripe(sh, &s);
 
+	if (s.want_cache) {
+		/* In last run of handle_stripe, we have finished
+		 * r5c_handle_stripe_dirtying and ops_run_biodrain, but
+		 * r5c_cache_data didn't finish because the journal device
+		 * didn't have enough space. This time we should continue
+		 * r5c_cache_data
+		 */
+		s.to_cache = s.want_cache;
+		goto finish;
+	}
+
 	if (test_bit(STRIPE_LOG_TRAPPED, &sh->state))
 		goto finish;
 
@@ -4348,7 +4438,7 @@ static void handle_stripe(struct stripe_head *sh)
 			struct r5dev *dev = &sh->dev[i];
 			if (test_bit(R5_LOCKED, &dev->flags) &&
 				(i == sh->pd_idx || i == sh->qd_idx ||
-				 dev->written)) {
+				 dev->written || test_bit(R5_InCache, &dev->flags))) {
 				pr_debug("Writing block %d\n", i);
 				set_bit(R5_Wantwrite, &dev->flags);
 				if (prexor)
@@ -4388,6 +4478,10 @@ static void handle_stripe(struct stripe_head *sh)
 				 test_bit(R5_Discard, &qdev->flags))))))
 		handle_stripe_clean_event(conf, sh, disks, &s.return_bi);
 
+	if (s.just_cached)
+		r5c_handle_cached_data_endio(conf, sh, disks, &s.return_bi);
+	r5l_stripe_write_finished(sh);
+
 	/* Now we might consider reading some blocks, either to check/generate
 	 * parity, or to satisfy requests
 	 * or to load a block that is being partially written.
@@ -6526,6 +6620,11 @@ static struct r5conf *setup_conf(struct mddev *mddev)
 	for (i = 0; i < NR_STRIPE_HASH_LOCKS; i++)
 		INIT_LIST_HEAD(conf->temp_inactive_list + i);
 
+	atomic_set(&conf->r5c_cached_full_stripes, 0);
+	INIT_LIST_HEAD(&conf->r5c_full_stripe_list);
+	atomic_set(&conf->r5c_cached_partial_stripes, 0);
+	INIT_LIST_HEAD(&conf->r5c_partial_stripe_list);
+
 	conf->level = mddev->new_level;
 	conf->chunk_sectors = mddev->new_chunk_sectors;
 	if (raid5_alloc_percpu(conf) != 0)
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 8bae64b..ac6d7c7 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -226,6 +226,7 @@ struct stripe_head {
 
 	struct r5l_io_unit	*log_io;
 	struct list_head	log_list;
+	atomic_t		dev_in_cache;
 	/**
 	 * struct stripe_operations
 	 * @target - STRIPE_OP_COMPUTE_BLK target
@@ -263,6 +264,7 @@ struct stripe_head_state {
 	 */
 	int syncing, expanding, expanded, replacing;
 	int locked, uptodate, to_read, to_write, failed, written;
+	int to_cache, want_cache, just_cached;
 	int to_fill, compute, req_compute, non_overwrite;
 	int failed_num[2];
 	int p_failed, q_failed;
@@ -313,6 +315,8 @@ enum r5dev_flags {
 			 */
 	R5_Discard,	/* Discard the stripe */
 	R5_SkipCopy,	/* Don't copy data from bio to stripe cache */
+	R5_Wantcache,	/* Want write data to write cache */
+	R5_InCache,	/* Data in cache */
 };
 
 /*
@@ -348,6 +352,12 @@ enum {
 	STRIPE_LOG_TRAPPED,	/* trapped into log */
 	STRIPE_R5C_FROZEN,	/* r5c_cache frozen and being written out */
 	STRIPE_R5C_WRITTEN,	/* ready for r5c_handle_stripe_written() */
+	STRIPE_R5C_PARTIAL_STRIPE,	/* in r5c cache (to-be/being handled or
+					 * in conf->r5c_partial_stripe_list)
+					 */
+	STRIPE_R5C_FULL_STRIPE,	/* in r5c cache (to-be/being handled or
+				 * in conf->r5c_full_stripe_list)
+				 */
 };
 
 #define STRIPE_EXPAND_SYNC_FLAGS \
@@ -600,6 +610,12 @@ struct r5conf {
 	 */
 	atomic_t		active_stripes;
 	struct list_head	inactive_list[NR_STRIPE_HASH_LOCKS];
+
+	atomic_t		r5c_cached_full_stripes;
+	struct list_head	r5c_full_stripe_list;
+	atomic_t		r5c_cached_partial_stripes;
+	struct list_head	r5c_partial_stripe_list;
+
 	atomic_t		empty_inactive_list_nr;
 	struct llist_head	released_stripes;
 	wait_queue_head_t	wait_for_quiescent;
@@ -720,4 +736,10 @@ r5c_handle_stripe_dirtying(struct r5conf *conf, struct stripe_head *sh,
 			   struct stripe_head_state *s, int disks);
 extern void
 r5c_handle_stripe_written(struct r5conf *conf, struct stripe_head *sh);
+extern void r5l_wake_reclaim(struct r5l_log *log, sector_t space);
+extern void r5c_handle_cached_data_endio(struct r5conf *conf,
+	struct stripe_head *sh, int disks, struct bio_list *return_bi);
+extern int r5c_cache_data(struct r5l_log *log, struct stripe_head *sh,
+			  struct stripe_head_state *s);
+extern void r5c_freeze_stripe_for_reclaim(struct stripe_head *sh);
 #endif
-- 
2.9.3

[PATCH v4 5/8] md/r5cache: reclaim support

[Song Liu]

There are two limited resources, stripe cache and journal disk space.
For better performance, we priotize reclaim of full stripe writes.
To free up more journal space, we free earliest data on the journal.

In current implementation, reclaim happens when:
1. every R5C_RECLAIM_WAKEUP_INTERVAL (5 seconds)
2. when there are R5C_FULL_STRIPE_FLUSH_BATCH (8) cached full stripes
   (r5c_check_cached_full_stripe)
3. when raid5_get_active_stripe sees pressure in stripe cache space
   (r5c_check_stripe_cache_usage)
4. when there is pressure in journal space.

1-3 above are straightforward. The following explains details of 4.

To avoid deadlock due to log space, we need to reserve enough space
to flush cached data. The size of required log space depends on total
number of cached stripes (stripe_in_cache_count). In current
implementation, the reclaim path automatically include pending
data writes with parity writes (similar to write through case).
Therefore, we need up to (conf->raid_disks + 1) pages for each cached
stripe (1 page for meta data, raid_disks pages for all data and
parity). r5c_log_required_to_flush_cache() calculates log space
required to flush cache. In the following, we refer to the space
calculated by r5c_log_required_to_flush_cache() as
reclaim_required_space.

Two flags are added to r5conf->cache_state: R5C_LOG_TIGHT and
R5C_LOG_CRITICAL. R5C_LOG_TIGHT is set when free space on the log
device is less than 3x of reclaim_required_space. R5C_LOG_CRITICAL
is set when free space on the log device is less than 2x of
reclaim_required_space.

r5c_cache keeps all data in cache (not fully committed to RAID) in
a list (stripe_in_cache_list). These stripes are in the order of their
first appearance on the journal. So the log tail (last_checkpoint)
should point to the journal_start of the first item in the list.

When R5C_LOG_TIGHT is set, r5l_reclaim_thread starts flushing out
stripes at the head of stripe_in_cache. When R5C_LOG_CRITICAL is
set, the state machine only writes data that are already in the
log device (in stripe_in_cache_list).

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 drivers/md/raid5-cache.c | 363 +++++++++++++++++++++++++++++++++++++++++++----
 drivers/md/raid5.c       |  17 +++
 drivers/md/raid5.h       |  39 +++--
 3 files changed, 383 insertions(+), 36 deletions(-)

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 92d3d7b..2774f93 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -29,12 +29,21 @@
 #define BLOCK_SECTORS (8)
 
 /*
- * reclaim runs every 1/4 disk size or 10G reclaimable space. This can prevent
- * recovery scans a very long log
+ * log->max_free_space is min(1/4 disk size, 10G reclaimable space).
+ *
+ * In write through mode, the reclaim runs every log->max_free_space.
+ * This can prevent the recovery scans for too long
  */
 #define RECLAIM_MAX_FREE_SPACE (10 * 1024 * 1024 * 2) /* sector */
 #define RECLAIM_MAX_FREE_SPACE_SHIFT (2)
 
+/* wake up reclaim thread periodically */
+#define R5C_RECLAIM_WAKEUP_INTERVAL (5 * HZ)
+/* start flush with these full stripes */
+#define R5C_FULL_STRIPE_FLUSH_BATCH 8
+/* reclaim stripes in groups */
+#define R5C_RECLAIM_STRIPE_GROUP (NR_STRIPE_HASH_LOCKS * 2)
+
 /*
  * We only need 2 bios per I/O unit to make progress, but ensure we
  * have a few more available to not get too tight.
@@ -141,6 +150,11 @@ struct r5l_log {
 
 	/* for r5c_cache */
 	enum r5c_state r5c_state;
+	struct list_head stripe_in_cache_list;	/* all stripes in r5cache, with
+						 * sh->log_start in order
+						 */
+	spinlock_t stripe_in_cache_lock;
+	atomic_t stripe_in_cache_count;
 };
 
 /*
@@ -257,6 +271,84 @@ void r5c_handle_cached_data_endio(struct r5conf *conf,
 }
 
 /*
+ * check whether we should flush some stripes to free up stripe cache
+ */
+void r5c_check_stripe_cache_usage(struct r5conf *conf)
+{
+	if (!r5c_is_writeback(conf->log))
+		return;
+	spin_lock(&conf->device_lock);
+	if ((atomic_read(&conf->r5c_cached_partial_stripes) +
+	     atomic_read(&conf->r5c_cached_full_stripes) >
+	     conf->min_nr_stripes * 3 / 4) ||
+	    atomic_read(&conf->empty_inactive_list_nr) > 0)
+		r5c_flush_cache(conf, R5C_RECLAIM_STRIPE_GROUP);
+	spin_unlock(&conf->device_lock);
+}
+
+/*
+ * flush cache when there are R5C_FULL_STRIPE_FLUSH_BATCH or more full
+ * stripes in the cache
+ */
+void r5c_check_cached_full_stripe(struct r5conf *conf)
+{
+	if (!r5c_is_writeback(conf->log))
+		return;
+	if (atomic_read(&conf->r5c_cached_full_stripes) >=
+	    R5C_FULL_STRIPE_FLUSH_BATCH)
+		r5l_wake_reclaim(conf->log, 0);
+}
+
+/*
+ * Total log space (in sectors) needed to flush all data in cache
+ *
+ * Currently, reclaim path 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 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 improve this, we will need reclaim path to be able to NOT include
+ * pending writes, which will reduce the requirement to
+ * (conf->max_degraded + 1) pages per stripe in cache.
+ */
+static sector_t r5c_log_required_to_flush_cache(struct r5conf *conf)
+{
+	struct r5l_log *log = conf->log;
+
+	if (!r5c_is_writeback(log))
+		return 0;
+
+	return BLOCK_SECTORS * (conf->raid_disks + 1) *
+		atomic_read(&log->stripe_in_cache_count);
+}
+
+/* evaluate log space usage and update R5C_LOG_TIGHT and R5C_LOG_CRITICAL */
+static inline void r5c_update_log_state(struct r5l_log *log)
+{
+	struct r5conf *conf = log->rdev->mddev->private;
+	sector_t free_space = r5l_ring_distance(log, log->log_start,
+						log->last_checkpoint);
+	sector_t reclaim_space = r5c_log_required_to_flush_cache(conf);
+
+	if (!r5c_is_writeback(log))
+		return;
+	else if (free_space < 2 * reclaim_space) {
+		set_bit(R5C_LOG_CRITICAL, &conf->cache_state);
+		set_bit(R5C_LOG_TIGHT, &conf->cache_state);
+	} else if (free_space < 3 * reclaim_space) {
+		clear_bit(R5C_LOG_CRITICAL, &conf->cache_state);
+		set_bit(R5C_LOG_TIGHT, &conf->cache_state);
+	} else if (free_space > 4 * reclaim_space) {
+		clear_bit(R5C_LOG_TIGHT, &conf->cache_state);
+		clear_bit(R5C_LOG_CRITICAL, &conf->cache_state);
+	} else
+		clear_bit(R5C_LOG_CRITICAL, &conf->cache_state);
+}
+
+/*
  * Freeze the stripe, thus send the stripe into reclaim path.
  *
  * In current implementation, STRIPE_R5C_FROZEN is also set in write through
@@ -290,6 +382,19 @@ void r5c_freeze_stripe_for_reclaim(struct stripe_head *sh)
 	}
 }
 
+/*
+ * do not release a stripe to cached lists in quiesce
+ */
+void r5c_prepare_stripe_for_release_in_quiesce(struct stripe_head *sh)
+{
+	if (!test_bit(STRIPE_HANDLE, &sh->state) &&
+	    atomic_read(&sh->dev_in_cache) != 0) {
+		if (!test_bit(STRIPE_R5C_FROZEN, &sh->state))
+			r5c_freeze_stripe_for_reclaim(sh);
+		set_bit(STRIPE_HANDLE, &sh->state);
+	}
+}
+
 static void r5c_handle_data_cached(struct stripe_head *sh)
 {
 	int i;
@@ -435,6 +540,7 @@ static void r5_reserve_log_entry(struct r5l_log *log, struct r5l_io_unit *io)
 {
 	log->log_start = r5l_ring_add(log, log->log_start, BLOCK_SECTORS);
 
+	r5c_update_log_state(log);
 	/*
 	 * If we filled up the log device start from the beginning again,
 	 * which will require a new bio.
@@ -552,6 +658,7 @@ static int r5l_log_stripe(struct r5l_log *log, struct stripe_head *sh,
 	int meta_size;
 	int ret;
 	struct r5l_io_unit *io;
+	unsigned long flags;
 
 	meta_size =
 		((sizeof(struct r5l_payload_data_parity) + sizeof(__le32))
@@ -595,20 +702,42 @@ static int r5l_log_stripe(struct r5l_log *log, struct stripe_head *sh,
 	atomic_inc(&io->pending_stripe);
 	sh->log_io = io;
 
+	if (log->r5c_state == R5C_STATE_WRITE_THROUGH)
+		return 0;
+
+	if (sh->log_start == MaxSector) {
+		BUG_ON(!list_empty(&sh->r5c));
+		sh->log_start = io->log_start;
+		spin_lock_irqsave(&log->stripe_in_cache_lock, flags);
+		list_add_tail(&sh->r5c,
+			      &log->stripe_in_cache_list);
+		spin_unlock_irqrestore(&log->stripe_in_cache_lock, flags);
+		atomic_inc(&log->stripe_in_cache_count);
+	}
 	return 0;
 }
 
+/* add stripe to no_space_stripes, and then wake up reclaim */
+static inline void r5l_add_no_space_stripe(struct r5l_log *log, struct stripe_head *sh)
+{
+	spin_lock(&log->no_space_stripes_lock);
+	list_add_tail(&sh->log_list, &log->no_space_stripes);
+	spin_unlock(&log->no_space_stripes_lock);
+}
+
 /*
  * running in raid5d, where reclaim could wait for raid5d too (when it flushes
  * data from log to raid disks), so we shouldn't wait for reclaim here
  */
 int r5l_write_stripe(struct r5l_log *log, struct stripe_head *sh)
 {
+	struct r5conf *conf = sh->raid_conf;
 	int write_disks = 0;
 	int data_pages, parity_pages;
 	int reserve;
 	int i;
 	int ret = 0;
+	bool wake_reclaim = false;
 
 	if (!log)
 		return -EAGAIN;
@@ -654,22 +783,49 @@ int r5l_write_stripe(struct r5l_log *log, struct stripe_head *sh)
 	mutex_lock(&log->io_mutex);
 	/* meta + data */
 	reserve = (1 + write_disks) << (PAGE_SHIFT - 9);
-	if (!r5l_has_free_space(log, reserve)) {
-		spin_lock(&log->no_space_stripes_lock);
-		list_add_tail(&sh->log_list, &log->no_space_stripes);
-		spin_unlock(&log->no_space_stripes_lock);
 
-		r5l_wake_reclaim(log, reserve);
-	} else {
-		ret = r5l_log_stripe(log, sh, data_pages, parity_pages);
-		if (ret) {
-			spin_lock_irq(&log->io_list_lock);
-			list_add_tail(&sh->log_list, &log->no_mem_stripes);
-			spin_unlock_irq(&log->io_list_lock);
+	if (log->r5c_state == R5C_STATE_WRITE_THROUGH) {
+		if (!r5l_has_free_space(log, reserve)) {
+			r5l_add_no_space_stripe(log, sh);
+			wake_reclaim = true;
+		} else {
+			ret = r5l_log_stripe(log, sh, data_pages, parity_pages);
+			if (ret) {
+				spin_lock_irq(&log->io_list_lock);
+				list_add_tail(&sh->log_list,
+					      &log->no_mem_stripes);
+				spin_unlock_irq(&log->io_list_lock);
+			}
+		}
+	} else {  /* R5C_STATE_WRITE_BACK */
+		/*
+		 * log space critical, do not process stripes that are
+		 * not in cache yet (sh->log_start == MaxSector).
+		 */
+		if (test_bit(R5C_LOG_CRITICAL, &conf->cache_state) &&
+		    sh->log_start == MaxSector) {
+			r5l_add_no_space_stripe(log, sh);
+			wake_reclaim = true;
+			reserve = 0;
+		} else if (!r5l_has_free_space(log, reserve)) {
+			if (sh->log_start == log->last_checkpoint)
+				BUG();
+			else {
+				r5l_add_no_space_stripe(log, sh);
+			}
+		} else {
+			ret = r5l_log_stripe(log, sh, data_pages, parity_pages);
+			if (ret) {
+				spin_lock_irq(&log->io_list_lock);
+				list_add_tail(&sh->log_list, &log->no_mem_stripes);
+				spin_unlock_irq(&log->io_list_lock);
+			}
 		}
 	}
 
 	mutex_unlock(&log->io_mutex);
+	if (wake_reclaim)
+		r5l_wake_reclaim(log, reserve);
 	return 0;
 }
 
@@ -709,6 +865,7 @@ static void r5l_run_no_space_stripes(struct r5l_log *log)
 	while (!list_empty(&log->no_space_stripes)) {
 		sh = list_first_entry(&log->no_space_stripes,
 				      struct stripe_head, log_list);
+		set_bit(STRIPE_PREREAD_ACTIVE, &sh->state);
 		list_del_init(&sh->log_list);
 		set_bit(STRIPE_HANDLE, &sh->state);
 		raid5_release_stripe(sh);
@@ -716,10 +873,40 @@ static void r5l_run_no_space_stripes(struct r5l_log *log)
 	spin_unlock(&log->no_space_stripes_lock);
 }
 
+/*
+ * calculate new last_checkpoint
+ * for write through mode, returns log->next_checkpoint
+ * for write back, returns log_start of first sh in stripe_in_cache_list
+ */
+static sector_t r5c_calculate_new_cp(struct r5conf *conf)
+{
+	struct stripe_head *sh;
+	struct r5l_log *log = conf->log;
+	sector_t end = MaxSector;
+	unsigned long flags;
+
+	if (log->r5c_state == R5C_STATE_WRITE_THROUGH)
+		return log->next_checkpoint;
+
+	spin_lock_irqsave(&log->stripe_in_cache_lock, flags);
+	if (list_empty(&conf->log->stripe_in_cache_list)) {
+		/* all stripes flushed */
+		spin_unlock_irqrestore(&log->stripe_in_cache_lock, flags);
+		return log->next_checkpoint;
+	}
+	sh = list_first_entry(&conf->log->stripe_in_cache_list,
+			      struct stripe_head, r5c);
+	end = sh->log_start;
+	spin_unlock_irqrestore(&log->stripe_in_cache_lock, flags);
+	return end;
+}
+
 static sector_t r5l_reclaimable_space(struct r5l_log *log)
 {
+	struct r5conf *conf = log->rdev->mddev->private;
+
 	return r5l_ring_distance(log, log->last_checkpoint,
-				 log->next_checkpoint);
+				 r5c_calculate_new_cp(conf));
 }
 
 static void r5l_run_no_mem_stripe(struct r5l_log *log)
@@ -765,6 +952,7 @@ static bool r5l_complete_finished_ios(struct r5l_log *log)
 static void __r5l_stripe_write_finished(struct r5l_io_unit *io)
 {
 	struct r5l_log *log = io->log;
+	struct r5conf *conf = log->rdev->mddev->private;
 	unsigned long flags;
 
 	spin_lock_irqsave(&log->io_list_lock, flags);
@@ -775,7 +963,8 @@ static void __r5l_stripe_write_finished(struct r5l_io_unit *io)
 		return;
 	}
 
-	if (r5l_reclaimable_space(log) > log->max_free_space)
+	if (r5l_reclaimable_space(log) > log->max_free_space ||
+	    test_bit(R5C_LOG_TIGHT, &conf->cache_state))
 		r5l_wake_reclaim(log, 0);
 
 	spin_unlock_irqrestore(&log->io_list_lock, flags);
@@ -898,10 +1087,10 @@ static void r5l_write_super_and_discard_space(struct r5l_log *log,
 
 static void r5l_do_reclaim(struct r5l_log *log)
 {
+	struct r5conf *conf = log->rdev->mddev->private;
 	sector_t reclaim_target = xchg(&log->reclaim_target, 0);
 	sector_t reclaimable;
 	sector_t next_checkpoint;
-	u64 next_cp_seq;
 
 	spin_lock_irq(&log->io_list_lock);
 	/*
@@ -924,8 +1113,7 @@ static void r5l_do_reclaim(struct r5l_log *log)
 				    log->io_list_lock);
 	}
 
-	next_checkpoint = log->next_checkpoint;
-	next_cp_seq = log->next_cp_seq;
+	next_checkpoint = r5c_calculate_new_cp(conf);
 	spin_unlock_irq(&log->io_list_lock);
 
 	BUG_ON(reclaimable < 0);
@@ -941,7 +1129,7 @@ static void r5l_do_reclaim(struct r5l_log *log)
 
 	mutex_lock(&log->io_mutex);
 	log->last_checkpoint = next_checkpoint;
-	log->last_cp_seq = next_cp_seq;
+	r5c_update_log_state(log);
 	mutex_unlock(&log->io_mutex);
 
 	r5l_run_no_space_stripes(log);
@@ -955,6 +1143,7 @@ static void r5l_reclaim_thread(struct md_thread *thread)
 
 	if (!log)
 		return;
+	r5c_do_reclaim(conf);
 	r5l_do_reclaim(log);
 }
 
@@ -963,6 +1152,8 @@ void r5l_wake_reclaim(struct r5l_log *log, sector_t space)
 	unsigned long target;
 	unsigned long new = (unsigned long)space; /* overflow in theory */
 
+	if (!log)
+		return;
 	do {
 		target = log->reclaim_target;
 		if (new < target)
@@ -986,11 +1177,12 @@ void r5l_quiesce(struct r5l_log *log, int state)
 			return;
 		log->reclaim_thread = md_register_thread(r5l_reclaim_thread,
 					log->rdev->mddev, "reclaim");
+		log->reclaim_thread->timeout = R5C_RECLAIM_WAKEUP_INTERVAL;
 	} else if (state == 1) {
 		/* make sure r5l_write_super_and_discard_space exits */
 		mddev = log->rdev->mddev;
 		wake_up(&mddev->sb_wait);
-		r5l_wake_reclaim(log, -1L);
+		r5l_wake_reclaim(log, MaxSector);
 		md_unregister_thread(&log->reclaim_thread);
 		r5l_do_reclaim(log);
 	}
@@ -1271,6 +1463,62 @@ static void r5l_write_super(struct r5l_log *log, sector_t cp)
 	set_bit(MD_CHANGE_DEVS, &mddev->flags);
 }
 
+/*
+ * r5c_flush_stripe moves stripe from cached list to handle_list. When called,
+ * the stripe must be on r5c_cached_full_stripes or r5c_cached_partial_stripes.
+ *
+ * must hold conf->device_lock
+ */
+static void r5c_flush_stripe(struct r5conf *conf, struct stripe_head *sh)
+{
+	BUG_ON(list_empty(&sh->lru));
+	BUG_ON(test_bit(STRIPE_R5C_FROZEN, &sh->state));
+	BUG_ON(test_bit(STRIPE_HANDLE, &sh->state));
+	assert_spin_locked(&conf->device_lock);
+
+	list_del_init(&sh->lru);
+	atomic_inc(&sh->count);
+
+	set_bit(STRIPE_HANDLE, &sh->state);
+	atomic_inc(&conf->active_stripes);
+	r5c_freeze_stripe_for_reclaim(sh);
+
+	set_bit(STRIPE_PREREAD_ACTIVE, &sh->state);
+	raid5_release_stripe(sh);
+}
+
+/*
+ * if num <= 0, flush all stripes
+ * if num > 0, flush at most num stripes
+ */
+int r5c_flush_cache(struct r5conf *conf, int num)
+{
+	int count = 0;
+	struct stripe_head *sh, *next;
+
+	assert_spin_locked(&conf->device_lock);
+	if (!conf->log)
+		return 0;
+
+	list_for_each_entry_safe(sh, next, &conf->r5c_full_stripe_list, lru) {
+		r5c_flush_stripe(conf, sh);
+		count++;
+		if (num > 0 && count >= num && count >=
+		    R5C_FULL_STRIPE_FLUSH_BATCH)
+			return count;
+	}
+
+	list_for_each_entry_safe(sh, next,
+				 &conf->r5c_partial_stripe_list, lru) {
+		r5c_flush_stripe(conf, sh);
+		count++;
+		if (num > 0 && count == num)
+			return count;
+	}
+
+	return count;
+}
+
 int r5c_handle_stripe_dirtying(struct r5conf *conf,
 			       struct stripe_head *sh,
 			       struct stripe_head_state *s,
@@ -1327,6 +1575,7 @@ void r5c_handle_stripe_written(struct r5conf *conf,
 {
 	int i;
 	int do_wakeup = 0;
+	unsigned long flags;
 
 	if (!test_and_clear_bit(STRIPE_R5C_WRITTEN, &sh->state))
 		return;
@@ -1349,12 +1598,22 @@ void r5c_handle_stripe_written(struct r5conf *conf,
 
 	if (do_wakeup)
 		wake_up(&conf->wait_for_overlap);
+
+	if (conf->log->r5c_state == R5C_STATE_WRITE_THROUGH)
+		return;
+
+	spin_lock_irqsave(&conf->log->stripe_in_cache_lock, flags);
+	list_del_init(&sh->r5c);
+	spin_unlock_irqrestore(&conf->log->stripe_in_cache_lock, flags);
+	sh->log_start = MaxSector;
+	atomic_dec(&conf->log->stripe_in_cache_count);
 }
 
 int
 r5c_cache_data(struct r5l_log *log, struct stripe_head *sh,
 	       struct stripe_head_state *s)
 {
+	struct r5conf *conf = sh->raid_conf;
 	int pages;
 	int reserve;
 	int i;
@@ -1387,12 +1646,15 @@ r5c_cache_data(struct r5l_log *log, struct stripe_head *sh,
 	mutex_lock(&log->io_mutex);
 	/* meta + data */
 	reserve = (1 + pages) << (PAGE_SHIFT - 9);
-	if (!r5l_has_free_space(log, reserve)) {
-		spin_lock(&log->no_space_stripes_lock);
-		list_add_tail(&sh->log_list, &log->no_space_stripes);
-		spin_unlock(&log->no_space_stripes_lock);
 
-		r5l_wake_reclaim(log, reserve);
+	if (test_bit(R5C_LOG_CRITICAL, &conf->cache_state) &&
+	    sh->log_start == MaxSector)
+		r5l_add_no_space_stripe(log, sh);
+	else if (!r5l_has_free_space(log, reserve)) {
+		if (sh->log_start == log->last_checkpoint)
+			BUG();
+		else
+			r5l_add_no_space_stripe(log, sh);
 	} else {
 		ret = r5l_log_stripe(log, sh, pages, 0);
 		if (ret) {
@@ -1406,6 +1668,49 @@ r5c_cache_data(struct r5l_log *log, struct stripe_head *sh,
 	return 0;
 }
 
+void r5c_do_reclaim(struct r5conf *conf)
+{
+	struct r5l_log *log = conf->log;
+	struct stripe_head *sh, *next;
+	int count = 0;
+	unsigned long flags;
+
+	if (!r5c_is_writeback(log))
+		return;
+
+	/* flush all full stripes */
+	spin_lock_irqsave(&conf->device_lock, flags);
+	list_for_each_entry_safe(sh, next, &conf->r5c_full_stripe_list, lru)
+		r5c_flush_stripe(conf, sh);
+	spin_unlock_irqrestore(&conf->device_lock, flags);
+
+	/* if log space is tight, flush stripes on stripe_in_cache_list */
+	if (test_bit(R5C_LOG_TIGHT, &conf->cache_state)) {
+		spin_lock_irqsave(&log->stripe_in_cache_lock, flags);
+		spin_lock(&conf->device_lock);
+		list_for_each_entry(sh, &log->stripe_in_cache_list, r5c) {
+			/*
+			 * stripes on stripe_in_cache_list could be in any
+			 * state of the stripe_cache state machine. In this
+			 * case, we only want to flush stripe on
+			 * r5c_cached_full/partial_stripes. The following
+			 * condition makes sure the stripe is on one of the
+			 * two lists.
+			 */
+			if (!list_empty(&sh->lru) &&
+			    !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_cache_lock, flags);
+	}
+	md_wakeup_thread(conf->mddev->thread);
+}
+
 static int r5l_load_log(struct r5l_log *log)
 {
 	struct md_rdev *rdev = log->rdev;
@@ -1463,6 +1768,9 @@ create:
 	if (log->max_free_space > RECLAIM_MAX_FREE_SPACE)
 		log->max_free_space = RECLAIM_MAX_FREE_SPACE;
 	log->last_checkpoint = cp;
+	mutex_lock(&log->io_mutex);
+	r5c_update_log_state(log);
+	mutex_unlock(&log->io_mutex);
 
 	__free_page(page);
 
@@ -1534,6 +1842,8 @@ int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
 						 log->rdev->mddev, "reclaim");
 	if (!log->reclaim_thread)
 		goto reclaim_thread;
+	log->reclaim_thread->timeout = R5C_RECLAIM_WAKEUP_INTERVAL;
+
 	init_waitqueue_head(&log->iounit_wait);
 
 	INIT_LIST_HEAD(&log->no_mem_stripes);
@@ -1542,6 +1852,9 @@ int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
 	spin_lock_init(&log->no_space_stripes_lock);
 
 	log->r5c_state = R5C_STATE_WRITE_THROUGH;
+	INIT_LIST_HEAD(&log->stripe_in_cache_list);
+	spin_lock_init(&log->stripe_in_cache_lock);
+	atomic_set(&log->stripe_in_cache_count, 0);
 
 	if (r5l_load_log(log))
 		goto error;
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 27fd183..0f3b0f4 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -220,6 +220,11 @@ static void do_release_stripe(struct r5conf *conf, struct stripe_head *sh,
 {
 	BUG_ON(!list_empty(&sh->lru));
 	BUG_ON(atomic_read(&conf->active_stripes)==0);
+
+	/* When quiesce in r5c write back, make sure the stripe is handled*/
+	if (conf->quiesce && r5c_is_writeback(conf->log))
+		r5c_prepare_stripe_for_release_in_quiesce(sh);
+
 	if (test_bit(STRIPE_HANDLE, &sh->state)) {
 		if (test_bit(STRIPE_DELAYED, &sh->state) &&
 		    !test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
@@ -256,6 +261,7 @@ static void do_release_stripe(struct r5conf *conf, struct stripe_head *sh,
 				if (test_and_clear_bit(STRIPE_R5C_PARTIAL_STRIPE, &sh->state))
 					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,
@@ -626,9 +632,12 @@ raid5_get_active_stripe(struct r5conf *conf, sector_t sector,
 			}
 			if (noblock && sh == NULL)
 				break;
+
+			r5c_check_stripe_cache_usage(conf);
 			if (!sh) {
 				set_bit(R5_INACTIVE_BLOCKED,
 					&conf->cache_state);
+				r5l_wake_reclaim(conf->log, 0);
 				wait_event_lock_irq(
 					conf->wait_for_stripe,
 					!list_empty(conf->inactive_list + hash) &&
@@ -854,6 +863,7 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
 
 	if (r5l_write_stripe(conf->log, sh) == 0)
 		return;
+
 	for (i = disks; i--; ) {
 		int op, op_flags = 0;
 		int replace_only = 0;
@@ -1983,8 +1993,10 @@ static struct stripe_head *alloc_stripe(struct kmem_cache *sc, gfp_t gfp,
 		spin_lock_init(&sh->batch_lock);
 		INIT_LIST_HEAD(&sh->batch_list);
 		INIT_LIST_HEAD(&sh->lru);
+		INIT_LIST_HEAD(&sh->r5c);
 		atomic_set(&sh->count, 1);
 		atomic_set(&sh->dev_in_cache, 0);
+		sh->log_start = MaxSector;
 		for (i = 0; i < disks; i++) {
 			struct r5dev *dev = &sh->dev[i];
 
@@ -4739,6 +4751,10 @@ static int raid5_congested(struct mddev *mddev, int bits)
 
 	if (test_bit(R5_INACTIVE_BLOCKED, &conf->cache_state))
 		return 1;
+
+	/* Also checks whether there is pressure on r5cache log space */
+	if (test_bit(R5C_LOG_TIGHT, &conf->cache_state))
+		return 1;
 	if (conf->quiesce)
 		return 1;
 	if (atomic_read(&conf->empty_inactive_list_nr))
@@ -7704,6 +7720,7 @@ static void raid5_quiesce(struct mddev *mddev, int state)
 		/* '2' tells resync/reshape to pause so that all
 		 * active stripes can drain
 		 */
+		r5c_flush_cache(conf, 0);
 		conf->quiesce = 2;
 		wait_event_cmd(conf->wait_for_quiescent,
 				    atomic_read(&conf->active_stripes) == 0 &&
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index ac6d7c7..d17eed4 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -227,6 +227,8 @@ struct stripe_head {
 	struct r5l_io_unit	*log_io;
 	struct list_head	log_list;
 	atomic_t		dev_in_cache;
+	sector_t		log_start; /* first meta block on the journal */
+	struct list_head	r5c; /* for r5c_cache->stripe_in_cache */
 	/**
 	 * struct stripe_operations
 	 * @target - STRIPE_OP_COMPUTE_BLK target
@@ -521,6 +523,26 @@ struct r5worker_group {
 	int stripes_cnt;
 };
 
+enum r5_cache_state {
+	R5_INACTIVE_BLOCKED,	/* release of inactive stripes blocked,
+				 * waiting for 25% to be free
+				 */
+	R5_ALLOC_MORE,		/* It might help to allocate another
+				 * stripe.
+				 */
+	R5_DID_ALLOC,		/* A stripe was allocated, don't allocate
+				 * more until at least one has been
+				 * released.  This avoids flooding
+				 * the cache.
+				 */
+	R5C_LOG_TIGHT,		/* journal device space tight, need to
+				 * prioritize stripes at last_checkpoint
+				 */
+	R5C_LOG_CRITICAL,	/* journal device is running out of space,
+				 * only process stripes at last_checkpoint
+				 */
+};
+
 struct r5conf {
 	struct hlist_head	*stripe_hashtbl;
 	/* only protect corresponding hash list and inactive_list */
@@ -622,17 +644,6 @@ struct r5conf {
 	wait_queue_head_t	wait_for_stripe;
 	wait_queue_head_t	wait_for_overlap;
 	unsigned long		cache_state;
-#define R5_INACTIVE_BLOCKED	1	/* release of inactive stripes blocked,
-					 * waiting for 25% to be free
-					 */
-#define R5_ALLOC_MORE		2	/* It might help to allocate another
-					 * stripe.
-					 */
-#define R5_DID_ALLOC		4	/* A stripe was allocated, don't allocate
-					 * more until at least one has been
-					 * released.  This avoids flooding
-					 * the cache.
-					 */
 	struct shrinker		shrinker;
 	int			pool_size; /* number of disks in stripeheads in pool */
 	spinlock_t		device_lock;
@@ -742,4 +753,10 @@ extern void r5c_handle_cached_data_endio(struct r5conf *conf,
 extern int r5c_cache_data(struct r5l_log *log, struct stripe_head *sh,
 			  struct stripe_head_state *s);
 extern void r5c_freeze_stripe_for_reclaim(struct stripe_head *sh);
+extern void r5c_prepare_stripe_for_release_in_quiesce(struct stripe_head *sh);
+extern void r5c_do_reclaim(struct r5conf *conf);
+extern int r5c_flush_cache(struct r5conf *conf, int num);
+extern void r5c_check_stripe_cache_usage(struct r5conf *conf);
+extern void r5c_check_cached_full_stripe(struct r5conf *conf);
+
 #endif
-- 
2.9.3

[PATCH v4 6/8] md/r5cache: sysfs entry r5c_state

[Song Liu]

r5c_state have 4 states:
* no-cache;
* write-through (write journal only);
* write-back (w/ write cache);
* cache-broken (journal missing or Faulty)

When there is functional write cache, r5c_state is a knob to
switch between write-back and write-through.

When the journal device is broken, the raid array is forced
in readonly mode. In this case, r5c_state can be used to
remove "journal feature", and thus make the array read-write
without journal. By writing into r5c_cache_mode, the array
can transit from cache-broken to no-cache, which removes
journal feature for the array.

To remove the journal feature:
- When journal fails, the raid array is forced readonly mode
  (enforced by kernel)
- User uses the new interface to remove journal (writing 0
  to r5c_state, I will add a mdadm option for that later)
- User forces array read-write;
- Kernel updates superblock and array can run read/write.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 drivers/md/raid5-cache.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++
 drivers/md/raid5.c       |  1 +
 drivers/md/raid5.h       |  1 +
 3 files changed, 60 insertions(+)

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 2774f93..b19024c 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -57,6 +57,8 @@ enum r5c_state {
 	R5C_STATE_CACHE_BROKEN = 3,
 };
 
+static char *r5c_state_str[] = {"no-cache", "write-through",
+				"write-back", "cache-broken"};
 /*
  * raid5 cache state machine
  *
@@ -1519,6 +1521,62 @@ int r5c_flush_cache(struct r5conf *conf, int num)
 	return count;
 }
 
+ssize_t r5c_state_show(struct mddev *mddev, char *page)
+{
+	struct r5conf *conf = mddev->private;
+	int val = 0;
+	int ret = 0;
+
+	if (conf->log)
+		val = conf->log->r5c_state;
+	else if (test_bit(MD_HAS_JOURNAL, &mddev->flags))
+		val = R5C_STATE_CACHE_BROKEN;
+	ret += snprintf(page, PAGE_SIZE - ret, "%d: %s\n",
+			val, r5c_state_str[val]);
+	return ret;
+}
+
+ssize_t r5c_state_store(struct mddev *mddev, const char *page, size_t len)
+{
+	struct r5conf *conf = mddev->private;
+	struct r5l_log *log = conf->log;
+	int val;
+
+	if (kstrtoint(page, 10, &val))
+		return -EINVAL;
+	if (!log && val != R5C_STATE_NO_CACHE)
+		return -EINVAL;
+
+	if (val < R5C_STATE_NO_CACHE || val > R5C_STATE_WRITE_BACK)
+		return -EINVAL;
+	if (val == R5C_STATE_NO_CACHE) {
+		if (conf->log &&
+		    !test_bit(Faulty, &log->rdev->flags)) {
+			pr_err("md/raid:%s: journal device is in use, cannot remove it\n",
+			       mdname(mddev));
+			return -EINVAL;
+		}
+	}
+
+	if (log) {
+		mddev_suspend(mddev);
+		conf->log->r5c_state = val;
+		mddev_resume(mddev);
+	}
+
+	if (val == R5C_STATE_NO_CACHE) {
+		clear_bit(MD_HAS_JOURNAL, &mddev->flags);
+		set_bit(MD_UPDATE_SB_FLAGS, &mddev->flags);
+	}
+	pr_info("md/raid:%s: setting r5c cache mode to %d: %s\n",
+		mdname(mddev), val, r5c_state_str[val]);
+	return len;
+}
+
+struct md_sysfs_entry
+r5c_state = __ATTR(r5c_state, S_IRUGO | S_IWUSR,
+		   r5c_state_show, r5c_state_store);
+
 int r5c_handle_stripe_dirtying(struct r5conf *conf,
 			       struct stripe_head *sh,
 			       struct stripe_head_state *s,
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 0f3b0f4..ffabde9 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -6295,6 +6295,7 @@ static struct attribute *raid5_attrs[] =  {
 	&raid5_group_thread_cnt.attr,
 	&raid5_skip_copy.attr,
 	&raid5_rmw_level.attr,
+	&r5c_state.attr,
 	NULL,
 };
 static struct attribute_group raid5_attrs_group = {
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index d17eed4..6898a76 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -758,5 +758,6 @@ extern void r5c_do_reclaim(struct r5conf *conf);
 extern int r5c_flush_cache(struct r5conf *conf, int num);
 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_state;
 
 #endif
-- 
2.9.3

[PATCH v4 7/8] md/r5cache: r5c recovery

[Song Liu]

This is the recovery part of raid5-cache.

With cache feature, there are 2 different scenarios of recovery:
1. Data-Parity stripe: a stripe with complete parity in journal.
2. Data-Only stripe: a stripe with only data in journal (or partial
   parity).

The code differentiate Data-Parity stripe from Data-Only stripe with
flag (STRIPE_R5C_WRITTEN).

For Data-Parity stripes, we use the same procedure as raid5 journal,
where all the data and parity are replayed to the RAID devices.

For Data-Only strips, we need to finish complete calculate parity and
finish the full reconstruct write or RMW write. For simplicity, in
the recovery, we load the stripe to stripe cache. Once the array is
started, the stripe cache state machine will handle these stripes
through normal write path.

r5c_recovery_flush_log contains the main procedure of recovery. The
recovery code first scans through the journal and loads data to
stripe cache. The code keeps tracks of all these stripes in a list
(use sh->lru and ctx->cached_list), stripes in the list are
organized in the order of its first appearance on the journal.
During the scan, the recovery code assesses each stripe as
Data-Parity or Data-Only.

During scan, the array may run out of stripe cache. In these cases,
the recovery code will also call raid5_set_cache_size to increase
stripe cache size.

At the end of scan, the recovery code replays all Data-Parity
stripes, and sets proper states for Data-Only stripes. The recovery
code also increases seq number by 10 and rewrites all Data-Only
stripes to journal. This is to avoid confusion after repeated
crashes. More details is explained in raid5-cache.c before
r5c_recovery_rewrite_data_only_stripes().

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 drivers/md/raid5-cache.c | 673 +++++++++++++++++++++++++++++++++++++----------
 1 file changed, 539 insertions(+), 134 deletions(-)

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index b19024c..b9fade3 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -1,5 +1,6 @@
 /*
  * Copyright (C) 2015 Shaohua Li <shli@fb.com>
+ * Copyright (C) 2016 Song Liu <songliubraving@fb.com>
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms and conditions of the GNU General Public License,
@@ -1211,10 +1212,13 @@ struct r5l_recovery_ctx {
 	sector_t meta_total_blocks;	/* total size of current meta and data */
 	sector_t pos;			/* recovery position */
 	u64 seq;			/* recovery position seq */
+	int data_parity_stripes;	/* number of data_parity stripes */
+	int data_only_stripes;		/* number of data_only stripes */
+	struct list_head cached_list;
 };
 
-static int r5l_read_meta_block(struct r5l_log *log,
-			       struct r5l_recovery_ctx *ctx)
+static int r5l_recovery_read_meta_block(struct r5l_log *log,
+					struct r5l_recovery_ctx *ctx)
 {
 	struct page *page = ctx->meta_page;
 	struct r5l_meta_block *mb;
@@ -1246,170 +1250,569 @@ static int r5l_read_meta_block(struct r5l_log *log,
 	return 0;
 }
 
-static int r5l_recovery_flush_one_stripe(struct r5l_log *log,
-					 struct r5l_recovery_ctx *ctx,
-					 sector_t stripe_sect,
-					 int *offset, sector_t *log_offset)
+/*
+ * r5l_recovery_load_data and r5l_recovery_load_parity uses flag R5_Wantwrite
+ * to mark valid (potentially not flushed) data in the journal.
+ *
+ * We already verified checksum in r5l_recovery_verify_data_checksum_for_mb,
+ * so there should not be any mismatch here.
+ */
+static void r5l_recovery_load_data(struct r5l_log *log,
+				   struct stripe_head *sh,
+				   struct r5l_recovery_ctx *ctx,
+				   struct r5l_payload_data_parity *payload,
+				   sector_t log_offset)
 {
-	struct r5conf *conf = log->rdev->mddev->private;
-	struct stripe_head *sh;
-	struct r5l_payload_data_parity *payload;
+	struct mddev *mddev = log->rdev->mddev;
+	struct r5conf *conf = mddev->private;
 	int disk_index;
 
-	sh = raid5_get_active_stripe(conf, stripe_sect, 0, 0, 0);
-	while (1) {
-		payload = page_address(ctx->meta_page) + *offset;
+	raid5_compute_sector(conf,
+			     le64_to_cpu(payload->location), 0,
+			     &disk_index, sh);
+	sync_page_io(log->rdev, log_offset, PAGE_SIZE,
+		     sh->dev[disk_index].page, REQ_OP_READ, 0, false);
+	sh->dev[disk_index].log_checksum =
+		le32_to_cpu(payload->checksum[0]);
+	ctx->meta_total_blocks += BLOCK_SECTORS;
 
-		if (le16_to_cpu(payload->header.type) == R5LOG_PAYLOAD_DATA) {
-			raid5_compute_sector(conf,
-					     le64_to_cpu(payload->location), 0,
-					     &disk_index, sh);
+	set_bit(R5_Wantwrite, &sh->dev[disk_index].flags);
+}
 
-			sync_page_io(log->rdev, *log_offset, PAGE_SIZE,
-				     sh->dev[disk_index].page, REQ_OP_READ, 0,
-				     false);
-			sh->dev[disk_index].log_checksum =
-				le32_to_cpu(payload->checksum[0]);
-			set_bit(R5_Wantwrite, &sh->dev[disk_index].flags);
-			ctx->meta_total_blocks += BLOCK_SECTORS;
-		} else {
-			disk_index = sh->pd_idx;
-			sync_page_io(log->rdev, *log_offset, PAGE_SIZE,
-				     sh->dev[disk_index].page, REQ_OP_READ, 0,
-				     false);
-			sh->dev[disk_index].log_checksum =
-				le32_to_cpu(payload->checksum[0]);
-			set_bit(R5_Wantwrite, &sh->dev[disk_index].flags);
-
-			if (sh->qd_idx >= 0) {
-				disk_index = sh->qd_idx;
-				sync_page_io(log->rdev,
-					     r5l_ring_add(log, *log_offset, BLOCK_SECTORS),
-					     PAGE_SIZE, sh->dev[disk_index].page,
-					     REQ_OP_READ, 0, false);
-				sh->dev[disk_index].log_checksum =
-					le32_to_cpu(payload->checksum[1]);
-				set_bit(R5_Wantwrite,
-					&sh->dev[disk_index].flags);
-			}
-			ctx->meta_total_blocks += BLOCK_SECTORS * conf->max_degraded;
-		}
+static void r5l_recovery_load_parity(struct r5l_log *log,
+				     struct stripe_head *sh,
+				     struct r5l_recovery_ctx *ctx,
+				     struct r5l_payload_data_parity *payload,
+				     sector_t log_offset)
+{
+	struct mddev *mddev = log->rdev->mddev;
+	struct r5conf *conf = mddev->private;
 
-		*log_offset = r5l_ring_add(log, *log_offset,
-					   le32_to_cpu(payload->size));
-		*offset += sizeof(struct r5l_payload_data_parity) +
-			sizeof(__le32) *
-			(le32_to_cpu(payload->size) >> (PAGE_SHIFT - 9));
-		if (le16_to_cpu(payload->header.type) == R5LOG_PAYLOAD_PARITY)
-			break;
+	ctx->meta_total_blocks += BLOCK_SECTORS * conf->max_degraded;
+	sync_page_io(log->rdev, log_offset, PAGE_SIZE,
+		     sh->dev[sh->pd_idx].page, REQ_OP_READ, 0, false);
+	sh->dev[sh->pd_idx].log_checksum =
+		le32_to_cpu(payload->checksum[0]);
+	set_bit(R5_Wantwrite, &sh->dev[sh->pd_idx].flags);
+
+	if (sh->qd_idx >= 0) {
+		sync_page_io(log->rdev,
+			     r5l_ring_add(log, log_offset, BLOCK_SECTORS),
+			     PAGE_SIZE, sh->dev[sh->qd_idx].page,
+			     REQ_OP_READ, 0, false);
+		sh->dev[sh->qd_idx].log_checksum =
+			le32_to_cpu(payload->checksum[1]);
+		set_bit(R5_Wantwrite, &sh->dev[sh->qd_idx].flags);
 	}
+	set_bit(STRIPE_R5C_WRITTEN, &sh->state);
+}
 
-	for (disk_index = 0; disk_index < sh->disks; disk_index++) {
-		void *addr;
-		u32 checksum;
+static void r5l_recovery_reset_stripe(struct stripe_head *sh)
+{
+	int i;
 
+	sh->state = 0;
+	sh->log_start = MaxSector;
+	for (i = sh->disks; i--; )
+		sh->dev[i].flags = 0;
+}
+
+static void
+r5l_recovery_replay_one_stripe(struct r5conf *conf,
+			       struct stripe_head *sh,
+			       struct r5l_recovery_ctx *ctx)
+{
+	struct md_rdev *rdev, *rrdev;
+	int disk_index;
+	int data_count = 0;
+
+	for (disk_index = 0; disk_index < sh->disks; disk_index++) {
 		if (!test_bit(R5_Wantwrite, &sh->dev[disk_index].flags))
 			continue;
-		addr = kmap_atomic(sh->dev[disk_index].page);
-		checksum = crc32c_le(log->uuid_checksum, addr, PAGE_SIZE);
-		kunmap_atomic(addr);
-		if (checksum != sh->dev[disk_index].log_checksum)
-			goto error;
+		if (disk_index == sh->qd_idx || disk_index == sh->pd_idx)
+			continue;
+		data_count++;
 	}
+	/* stripes only have parity are already flushed to RAID */
+	if (data_count == 0)
+		goto out;
 
 	for (disk_index = 0; disk_index < sh->disks; disk_index++) {
-		struct md_rdev *rdev, *rrdev;
-
-		if (!test_and_clear_bit(R5_Wantwrite,
-					&sh->dev[disk_index].flags))
+		if (!test_bit(R5_Wantwrite, &sh->dev[disk_index].flags))
 			continue;
 
 		/* in case device is broken */
 		rdev = rcu_dereference(conf->disks[disk_index].rdev);
 		if (rdev)
-			sync_page_io(rdev, stripe_sect, PAGE_SIZE,
+			sync_page_io(rdev, sh->sector, PAGE_SIZE,
 				     sh->dev[disk_index].page, REQ_OP_WRITE, 0,
 				     false);
 		rrdev = rcu_dereference(conf->disks[disk_index].replacement);
 		if (rrdev)
-			sync_page_io(rrdev, stripe_sect, PAGE_SIZE,
+			sync_page_io(rrdev, sh->sector, PAGE_SIZE,
 				     sh->dev[disk_index].page, REQ_OP_WRITE, 0,
 				     false);
 	}
-	raid5_release_stripe(sh);
+	ctx->data_parity_stripes++;
+out:
+	r5l_recovery_reset_stripe(sh);
+}
+
+static void
+r5l_recovery_create_emtpy_meta_block(struct r5l_log *log,
+				     struct page *page,
+				     sector_t pos, u64 seq)
+{
+	struct r5l_meta_block *mb;
+	u32 crc;
+
+	mb = page_address(page);
+	clear_page(mb);
+	mb->magic = cpu_to_le32(R5LOG_MAGIC);
+	mb->version = R5LOG_VERSION;
+	mb->meta_size = cpu_to_le32(sizeof(struct r5l_meta_block));
+	mb->seq = cpu_to_le64(seq);
+	mb->position = cpu_to_le64(pos);
+	crc = crc32c_le(log->uuid_checksum, mb, PAGE_SIZE);
+	mb->checksum = cpu_to_le32(crc);
+}
+
+static int r5l_log_write_empty_meta_block(struct r5l_log *log, sector_t pos,
+					  u64 seq)
+{
+	struct page *page;
+
+	page = alloc_page(GFP_KERNEL);
+	if (!page)
+		return -ENOMEM;
+	r5l_recovery_create_emtpy_meta_block(log, page, pos, seq);
+	if (!sync_page_io(log->rdev, pos, PAGE_SIZE, page, REQ_OP_WRITE,
+			  WRITE_FUA, false)) {
+		__free_page(page);
+		return -EIO;
+	}
+	__free_page(page);
 	return 0;
+}
 
-error:
-	for (disk_index = 0; disk_index < sh->disks; disk_index++)
-		sh->dev[disk_index].flags = 0;
-	raid5_release_stripe(sh);
-	return -EINVAL;
+static struct stripe_head *
+r5c_recovery_alloc_stripe(struct r5conf *conf,
+			  struct list_head *recovery_list,
+			  sector_t stripe_sect,
+			  sector_t log_start)
+{
+	struct stripe_head *sh;
+
+	sh = raid5_get_active_stripe(conf, stripe_sect, 0, 1, 0);
+	if (!sh)
+		return NULL;  /* no more stripe available */
+
+	r5l_recovery_reset_stripe(sh);
+	sh->log_start = log_start;
+
+	return sh;
 }
 
-static int r5l_recovery_flush_one_meta(struct r5l_log *log,
-				       struct r5l_recovery_ctx *ctx)
+static struct stripe_head *
+r5c_recovery_lookup_stripe(struct list_head *list, sector_t sect)
 {
-	struct r5conf *conf = log->rdev->mddev->private;
+	struct stripe_head *sh;
+
+	list_for_each_entry(sh, list, lru)
+		if (sh->sector == sect)
+			return sh;
+	return NULL;
+}
+
+static void
+r5c_recovery_replay_stripes(struct list_head *cached_stripe_list,
+			    struct r5l_recovery_ctx *ctx)
+{
+	struct stripe_head *sh, *next;
+
+	list_for_each_entry_safe(sh, next, cached_stripe_list, lru)
+		if (test_bit(STRIPE_R5C_WRITTEN, &sh->state)) {
+			r5l_recovery_replay_one_stripe(sh->raid_conf, sh, ctx);
+			list_del_init(&sh->lru);
+			raid5_release_stripe(sh);
+		}
+}
+
+/* returns 0 for match; 1 for mismtach */
+static int
+r5l_recovery_verify_data_checksum(struct r5l_log *log, struct page *page,
+				  sector_t log_offset, __le32 log_checksum)
+{
+	void *addr;
+	u32 checksum;
+
+	sync_page_io(log->rdev, log_offset, PAGE_SIZE,
+		     page, REQ_OP_READ, 0, false);
+	addr = kmap_atomic(page);
+	checksum = crc32c_le(log->uuid_checksum, addr, PAGE_SIZE);
+	kunmap_atomic(addr);
+	return le32_to_cpu(log_checksum) != checksum;
+}
+
+/*
+ * before loading data to stripe cache, we need verify checksum for all data,
+ * if there is mismatch for any data page, we drop all data in the mata block
+ */
+static int
+r5l_recovery_verify_data_checksum_for_mb(struct r5l_log *log,
+					 struct r5l_recovery_ctx *ctx)
+{
+	struct mddev *mddev = log->rdev->mddev;
+	struct r5conf *conf = mddev->private;
+	struct r5l_meta_block *mb = page_address(ctx->meta_page);
+	sector_t mb_offset = sizeof(struct r5l_meta_block);
+	sector_t log_offset = r5l_ring_add(log, ctx->pos, BLOCK_SECTORS);
+	struct page *page;
 	struct r5l_payload_data_parity *payload;
+
+	page = alloc_page(GFP_KERNEL);
+	if (!page)
+		return -ENOMEM;
+
+	while (mb_offset < le32_to_cpu(mb->meta_size)) {
+		payload = (void *)mb + mb_offset;
+
+		if (payload->header.type == R5LOG_PAYLOAD_DATA) {
+			if (r5l_recovery_verify_data_checksum(
+				    log, page, log_offset,
+				    payload->checksum[0]))
+				goto mismatch;
+		} else if (payload->header.type == R5LOG_PAYLOAD_PARITY) {
+			if (r5l_recovery_verify_data_checksum(
+				    log, page, log_offset,
+				    payload->checksum[0]))
+				goto mismatch;
+			if (conf->max_degraded == 2 && /* q for RAID 6 */
+			    r5l_recovery_verify_data_checksum(
+				    log, page,
+				    r5l_ring_add(log, log_offset,
+						 BLOCK_SECTORS),
+				    payload->checksum[1]))
+				goto mismatch;
+		} else
+			goto mismatch;
+
+		log_offset = r5l_ring_add(log, log_offset,
+					  le32_to_cpu(payload->size));
+
+		mb_offset += sizeof(struct r5l_payload_data_parity) +
+			sizeof(__le32) *
+			(le32_to_cpu(payload->size) >> (PAGE_SHIFT - 9));
+	}
+
+	put_page(page);
+	return 0;
+
+mismatch:
+	put_page(page);
+	return -EINVAL;
+}
+
+static int
+r5c_recovery_analyze_meta_block(struct r5l_log *log,
+				struct r5l_recovery_ctx *ctx,
+				struct list_head *cached_stripe_list)
+{
+	struct mddev *mddev = log->rdev->mddev;
+	struct r5conf *conf = mddev->private;
 	struct r5l_meta_block *mb;
-	int offset;
+	struct r5l_payload_data_parity *payload;
+	int mb_offset;
 	sector_t log_offset;
-	sector_t stripe_sector;
+	sector_t stripe_sect;
+	struct stripe_head *sh;
+	int ret;
+
+	/*
+	 * for mismatch in data blocks, we will drop all data in this mb, but
+	 * we will still read next mb for other data with FLUSH flag, as
+	 * io_unit could finish out of order.
+	 */
+	ret = r5l_recovery_verify_data_checksum_for_mb(log, ctx);
+	if (ret == -EINVAL)
+		return -EAGAIN;
+	else if (ret)
+		return ret;
 
 	mb = page_address(ctx->meta_page);
-	offset = sizeof(struct r5l_meta_block);
+	mb_offset = sizeof(struct r5l_meta_block);
 	log_offset = r5l_ring_add(log, ctx->pos, BLOCK_SECTORS);
 
-	while (offset < le32_to_cpu(mb->meta_size)) {
+	while (mb_offset < le32_to_cpu(mb->meta_size)) {
 		int dd;
 
-		payload = (void *)mb + offset;
-		stripe_sector = raid5_compute_sector(conf,
-						     le64_to_cpu(payload->location), 0, &dd, NULL);
-		if (r5l_recovery_flush_one_stripe(log, ctx, stripe_sector,
-						  &offset, &log_offset))
+		payload = (void *)mb + mb_offset;
+		stripe_sect = (payload->header.type == R5LOG_PAYLOAD_DATA) ?
+			raid5_compute_sector(
+				conf, le64_to_cpu(payload->location), 0, &dd,
+				NULL)
+			: le64_to_cpu(payload->location);
+
+		sh = r5c_recovery_lookup_stripe(cached_stripe_list,
+						stripe_sect);
+
+		if (!sh) {
+			sh = r5c_recovery_alloc_stripe(conf, cached_stripe_list,
+						       stripe_sect, ctx->pos);
+			if (!sh) {
+				pr_info("md/raid:%s: Increasing stripe cache size to %d to recovery data on journal.\n",
+					mdname(mddev),
+					conf->min_nr_stripes * 2);
+				raid5_set_cache_size(mddev,
+						     conf->min_nr_stripes * 2);
+				sh = r5c_recovery_alloc_stripe(
+					conf, cached_stripe_list, stripe_sect,
+					ctx->pos);
+			}
+			if (!sh) {
+				pr_err("md/raid:%s: Cannot get enough stripe_cache. Recovery interrupted.\n",
+				       mdname(mddev));
+				return -ENOMEM;
+			}
+			list_add_tail(&sh->lru, cached_stripe_list);
+		}
+		if (!sh)
+			return -ENOMEM;
+
+		if (payload->header.type == R5LOG_PAYLOAD_DATA) {
+			if (test_bit(STRIPE_R5C_WRITTEN, &sh->state)) {
+				r5l_recovery_reset_stripe(sh);
+				sh->log_start = ctx->pos;
+				list_move_tail(&sh->lru, cached_stripe_list);
+			}
+			r5l_recovery_load_data(log, sh, ctx, payload,
+					       log_offset);
+		} else if (payload->header.type == R5LOG_PAYLOAD_PARITY)
+			r5l_recovery_load_parity(log, sh, ctx, payload,
+						 log_offset);
+		else
 			return -EINVAL;
+
+		log_offset = r5l_ring_add(log, log_offset,
+					  le32_to_cpu(payload->size));
+
+		mb_offset += sizeof(struct r5l_payload_data_parity) +
+			sizeof(__le32) *
+			(le32_to_cpu(payload->size) >> (PAGE_SHIFT - 9));
 	}
+
 	return 0;
 }
 
-/* copy data/parity from log to raid disks */
-static void r5l_recovery_flush_log(struct r5l_log *log,
+/*
+ * Load the stripe into cache. The stripe will be written out later by
+ * the stripe cache state machine.
+ */
+static void r5c_recovery_load_one_stripe(struct r5l_log *log,
+					 struct stripe_head *sh)
+{
+	struct r5conf *conf = sh->raid_conf;
+	struct r5dev *dev;
+	int i;
+
+	atomic_set(&sh->dev_in_cache, 0);
+	for (i = sh->disks; i--; ) {
+		dev = sh->dev + i;
+		if (test_and_clear_bit(R5_Wantwrite, &dev->flags)) {
+			set_bit(R5_InCache, &dev->flags);
+			atomic_inc(&sh->dev_in_cache);
+		}
+	}
+	set_bit(STRIPE_R5C_PARTIAL_STRIPE, &sh->state);
+	atomic_inc(&conf->r5c_cached_partial_stripes);
+	list_add_tail(&sh->r5c, &log->stripe_in_cache_list);
+}
+
+/*
+ * Scan through the log for all to-be-flushed data
+ *
+ * For stripes with data and parity, namely Data-Parity stripe
+ * (STRIPE_R5C_WRITTEN == 0), we simply replay all the writes.
+ *
+ * For stripes with only data, namely Data-Only stripe
+ * (STRIPE_R5C_WRITTEN == 1), we load them to stripe cache state machine.
+ *
+ * For a stripe, if we see data after parity, we should discard all previous
+ * data and parity for this stripe, as these data are already flushed to
+ * the array.
+ *
+ * At the end of the scan, we return the new journal_tail, which points to
+ * first data-only stripe on the journal device, or next invalid meta block.
+ */
+static void r5c_recovery_flush_log(struct r5l_log *log,
 				   struct r5l_recovery_ctx *ctx)
 {
+	struct stripe_head *sh, *next;
+	int ret;
+
+	/* scan through the log */
 	while (1) {
-		if (r5l_read_meta_block(log, ctx))
-			return;
-		if (r5l_recovery_flush_one_meta(log, ctx))
-			return;
+		if (r5l_recovery_read_meta_block(log, ctx))
+			break;
+
+		ret = r5c_recovery_analyze_meta_block(log, ctx,
+						      &ctx->cached_list);
+		/*
+		 * -EAGAIN means mismatch in data block, in this case, we still
+		 * try scan the next metablock
+		 */
+		if (ret && ret != -EAGAIN)
+			break;
 		ctx->seq++;
 		ctx->pos = r5l_ring_add(log, ctx->pos, ctx->meta_total_blocks);
 	}
+
+	/* replay data-parity stripes */
+	r5c_recovery_replay_stripes(&ctx->cached_list, ctx);
+
+	/* load data-only stripes to stripe cache */
+	list_for_each_entry_safe(sh, next, &ctx->cached_list, lru) {
+		WARN_ON(test_bit(STRIPE_R5C_WRITTEN, &sh->state));
+		r5c_recovery_load_one_stripe(log, sh);
+		list_del_init(&sh->lru);
+		raid5_release_stripe(sh);
+		ctx->data_only_stripes++;
+	}
+
+	return;
 }
 
-static int r5l_log_write_empty_meta_block(struct r5l_log *log, sector_t pos,
-					  u64 seq)
+/*
+ * we did a recovery. Now ctx.pos points to an invalid meta block. New
+ * log will start here. but we can't let superblock point to last valid
+ * meta block. The log might looks like:
+ * | meta 1| meta 2| meta 3|
+ * meta 1 is valid, meta 2 is invalid. meta 3 could be valid. If
+ * superblock points to meta 1, we write a new valid meta 2n.  if crash
+ * happens again, new recovery will start from meta 1. Since meta 2n is
+ * valid now, recovery will think meta 3 is valid, which is wrong.
+ * The solution is we create a new meta in meta2 with its seq == meta
+ * 1's seq + 10 and let superblock points to meta2. The same recovery will
+ * not think meta 3 is a valid meta, because its seq doesn't match
+ */
+
+/*
+ * Before recovery, the log looks like the following
+ *
+ *   ---------------------------------------------
+ *   |           valid log        | invalid log  |
+ *   ---------------------------------------------
+ *   ^
+ *   |- log->last_checkpoint
+ *   |- log->last_cp_seq
+ *
+ * Now we scan through the log until we see invalid entry
+ *
+ *   ---------------------------------------------
+ *   |           valid log        | invalid log  |
+ *   ---------------------------------------------
+ *   ^                            ^
+ *   |- log->last_checkpoint      |- ctx->pos
+ *   |- log->last_cp_seq          |- ctx->seq
+ *
+ * From this point, we need to increase seq number by 10 to avoid
+ * confusing next recovery.
+ *
+ *   ---------------------------------------------
+ *   |           valid log        | invalid log  |
+ *   ---------------------------------------------
+ *   ^                              ^
+ *   |- log->last_checkpoint        |- ctx->pos+1
+ *   |- log->last_cp_seq            |- ctx->seq+11
+ *
+ * However, it is not safe to start the state machine yet, because data only
+ * parities are not yet secured in RAID. To save these data only parities, we
+ * rewrite them from seq+11.
+ *
+ *   -----------------------------------------------------------------
+ *   |           valid log        | data only stripes | invalid log  |
+ *   -----------------------------------------------------------------
+ *   ^                                                ^
+ *   |- log->last_checkpoint                          |- ctx->pos+n
+ *   |- log->last_cp_seq                              |- ctx->seq+10+n
+ *
+ * If failure happens again during this process, the recovery can safe start
+ * again from log->last_checkpoint.
+ *
+ * Once data only stripes are rewritten to journal, we move log_tail
+ *
+ *   -----------------------------------------------------------------
+ *   |     old log        |    data only stripes    | invalid log  |
+ *   -----------------------------------------------------------------
+ *                        ^                         ^
+ *                        |- log->last_checkpoint   |- ctx->pos+n
+ *                        |- log->last_cp_seq       |- ctx->seq+10+n
+ *
+ * Then we can safely start the state machine. If failure happens from this
+ * point on, the recovery will start from new log->last_checkpoint.
+ */
+static int
+r5c_recovery_rewrite_data_only_stripes(struct r5l_log *log,
+				       struct r5l_recovery_ctx *ctx)
 {
+	struct stripe_head *sh;
+	struct mddev *mddev = log->rdev->mddev;
 	struct page *page;
-	struct r5l_meta_block *mb;
-	u32 crc;
 
-	page = alloc_page(GFP_KERNEL | __GFP_ZERO);
-	if (!page)
+	page = alloc_page(GFP_KERNEL);
+	if (!page) {
+		pr_err("md/raid:%s: cannot allocate memory to rewrite data only stripes\n",
+		       mdname(mddev));
 		return -ENOMEM;
-	mb = page_address(page);
-	mb->magic = cpu_to_le32(R5LOG_MAGIC);
-	mb->version = R5LOG_VERSION;
-	mb->meta_size = cpu_to_le32(sizeof(struct r5l_meta_block));
-	mb->seq = cpu_to_le64(seq);
-	mb->position = cpu_to_le64(pos);
-	crc = crc32c_le(log->uuid_checksum, mb, PAGE_SIZE);
-	mb->checksum = cpu_to_le32(crc);
+	}
 
-	if (!sync_page_io(log->rdev, pos, PAGE_SIZE, page, REQ_OP_WRITE,
-			  WRITE_FUA, false)) {
-		__free_page(page);
-		return -EIO;
+	ctx->seq += 10;
+	list_for_each_entry(sh, &ctx->cached_list, lru) {
+		struct r5l_meta_block *mb;
+		int i;
+		int offset;
+		sector_t write_pos;
+
+		WARN_ON(test_bit(STRIPE_R5C_WRITTEN, &sh->state));
+		r5l_recovery_create_emtpy_meta_block(log, page,
+						     ctx->pos, ctx->seq);
+		mb = page_address(page);
+		offset = le32_to_cpu(mb->meta_size);
+		write_pos = ctx->pos + BLOCK_SECTORS;
+
+		for (i = sh->disks; i--; ) {
+			struct r5dev *dev = &sh->dev[i];
+			struct r5l_payload_data_parity *payload;
+			void *addr;
+
+			if (test_bit(R5_InCache, &dev->flags)) {
+				payload = (void *)mb + offset;
+				payload->header.type = cpu_to_le16(
+					R5LOG_PAYLOAD_DATA);
+				payload->size = BLOCK_SECTORS;
+				payload->location = cpu_to_le64(
+					raid5_compute_blocknr(sh, i, 0));
+				addr = kmap_atomic(dev->page);
+				payload->checksum[0] = cpu_to_le32(
+					crc32c_le(log->uuid_checksum, addr,
+						  PAGE_SIZE));
+				kunmap_atomic(addr);
+				sync_page_io(log->rdev, write_pos, PAGE_SIZE,
+					     dev->page, REQ_OP_WRITE, 0, false);
+				write_pos = r5l_ring_add(log, write_pos,
+							 BLOCK_SECTORS);
+				offset += sizeof(__le32) +
+					sizeof(struct r5l_payload_data_parity);
+
+			}
+		}
+		mb->meta_size = cpu_to_le32(offset);
+		mb->checksum = crc32c_le(log->uuid_checksum, mb, PAGE_SIZE);
+		sync_page_io(log->rdev, ctx->pos, PAGE_SIZE, page,
+			     REQ_OP_WRITE, WRITE_FUA, false);
+		sh->log_start = ctx->pos;
+		ctx->pos = write_pos;
+		ctx->seq += 1;
 	}
 	__free_page(page);
 	return 0;
@@ -1417,43 +1820,45 @@ static int r5l_log_write_empty_meta_block(struct r5l_log *log, sector_t pos,
 
 static int r5l_recovery_log(struct r5l_log *log)
 {
+	struct mddev *mddev = log->rdev->mddev;
 	struct r5l_recovery_ctx ctx;
 
 	ctx.pos = log->last_checkpoint;
 	ctx.seq = log->last_cp_seq;
 	ctx.meta_page = alloc_page(GFP_KERNEL);
+	ctx.data_only_stripes = 0;
+	ctx.data_parity_stripes = 0;
+	INIT_LIST_HEAD(&ctx.cached_list);
+
 	if (!ctx.meta_page)
 		return -ENOMEM;
 
-	r5l_recovery_flush_log(log, &ctx);
+	r5c_recovery_flush_log(log, &ctx);
+
 	__free_page(ctx.meta_page);
 
-	/*
-	 * we did a recovery. Now ctx.pos points to an invalid meta block. New
-	 * log will start here. but we can't let superblock point to last valid
-	 * meta block. The log might looks like:
-	 * | meta 1| meta 2| meta 3|
-	 * meta 1 is valid, meta 2 is invalid. meta 3 could be valid. If
-	 * superblock points to meta 1, we write a new valid meta 2n.  if crash
-	 * happens again, new recovery will start from meta 1. Since meta 2n is
-	 * valid now, recovery will think meta 3 is valid, which is wrong.
-	 * The solution is we create a new meta in meta2 with its seq == meta
-	 * 1's seq + 10 and let superblock points to meta2. The same recovery will
-	 * not think meta 3 is a valid meta, because its seq doesn't match
-	 */
-	if (ctx.seq > log->last_cp_seq + 1) {
-		int ret;
-
-		ret = r5l_log_write_empty_meta_block(log, ctx.pos, ctx.seq + 10);
-		if (ret)
-			return ret;
-		log->seq = ctx.seq + 11;
-		log->log_start = r5l_ring_add(log, ctx.pos, BLOCK_SECTORS);
-		r5l_write_super(log, ctx.pos);
-	} else {
-		log->log_start = ctx.pos;
-		log->seq = ctx.seq;
+	if ((ctx.data_only_stripes == 0) && (ctx.data_parity_stripes == 0))
+		pr_info("md/raid:%s: starting from clean shutdown\n",
+			mdname(mddev));
+	else {
+		pr_info("md/raid:%s: recoverying %d data-only stripes and %d data-parity stripes\n",
+			mdname(mddev), ctx.data_only_stripes,
+			ctx.data_parity_stripes);
+
+		if (ctx.data_only_stripes > 0)
+			if (r5c_recovery_rewrite_data_only_stripes(log, &ctx)) {
+				pr_err("md/raid:%s: failed to rewrite stripes to journal\n",
+				       mdname(mddev));
+				return -EIO;
+			}
 	}
+
+	log->log_start = ctx.pos;
+	log->next_checkpoint = ctx.pos;
+	log->seq = ctx.seq;
+	r5l_log_write_empty_meta_block(log, ctx.pos, ctx.seq);
+	r5l_write_super(log, ctx.pos);
+
 	return 0;
 }
 
-- 
2.9.3

[PATCH v4 8/8] md/r5cache: handle SYNC and FUA

[Song Liu]

With raid5 cache, we committing data from journal device. When
there is flush request, we need to flush journal device's cache.
This was not needed in raid5 journal, because we will flush the
journal before committing data to raid disks.

This is similar to FUA, except that we also need flush journal for
FUA. Otherwise, corruptions in earlier meta data will stop recovery
from reaching FUA data.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 drivers/md/raid5-cache.c | 162 +++++++++++++++++++++++++++++++++++++++++------
 drivers/md/raid5.c       |   8 +++
 drivers/md/raid5.h       |   1 +
 3 files changed, 153 insertions(+), 18 deletions(-)

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index b9fade3..f78ee8c 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -19,6 +19,7 @@
 #include <linux/raid/md_p.h>
 #include <linux/crc32c.h>
 #include <linux/random.h>
+#include <trace/events/block.h>
 #include "md.h"
 #include "raid5.h"
 #include "bitmap.h"
@@ -158,6 +159,9 @@ struct r5l_log {
 						 */
 	spinlock_t stripe_in_cache_lock;
 	atomic_t stripe_in_cache_count;
+
+	/* to submit async io_units, to fulfill ordering of flush */
+	struct work_struct deferred_io_work;
 };
 
 /*
@@ -184,6 +188,18 @@ struct r5l_io_unit {
 
 	int state;
 	bool need_split_bio;
+	struct bio *split_bio;
+
+	unsigned int has_flush:1;      /* include flush request */
+	unsigned int has_fua:1;        /* include fua request */
+	unsigned int has_null_flush:1; /* include empty flush request */
+	/*
+	 * io isn't sent yet, flush/fua request can only be submitted till it's
+	 * the first IO in running_ios list
+	 */
+	unsigned int io_deferred:1;
+
+	struct bio_list flush_barriers;   /* size == 0 flush bios */
 };
 
 /* r5l_io_unit state */
@@ -481,9 +497,11 @@ static void r5l_move_to_end_ios(struct r5l_log *log)
 	}
 }
 
+static void __r5l_stripe_write_finished(struct r5l_io_unit *io);
 static void r5l_log_endio(struct bio *bio)
 {
 	struct r5l_io_unit *io = bio->bi_private;
+	struct r5l_io_unit *io_deferred;
 	struct r5l_log *log = io->log;
 	unsigned long flags;
 
@@ -499,18 +517,89 @@ static void r5l_log_endio(struct bio *bio)
 		r5l_move_to_end_ios(log);
 	else
 		r5l_log_run_stripes(log);
+	if (!list_empty(&log->running_ios)) {
+		/*
+		 * FLUSH/FUA io_unit is deferred because of ordering, now we
+		 * can dispatch it
+		 */
+		io_deferred = list_first_entry(&log->running_ios,
+					       struct r5l_io_unit, log_sibling);
+		if (io_deferred->io_deferred)
+			schedule_work(&log->deferred_io_work);
+	}
+
 	spin_unlock_irqrestore(&log->io_list_lock, flags);
 
 	if (log->need_cache_flush)
 		md_wakeup_thread(log->rdev->mddev->thread);
+
+	if (io->has_null_flush) {
+		struct bio *bi;
+
+		WARN_ON(bio_list_empty(&io->flush_barriers));
+		while ((bi = bio_list_pop(&io->flush_barriers)) != NULL) {
+			bio_endio(bi);
+			atomic_dec(&io->pending_stripe);
+		}
+		if (atomic_read(&io->pending_stripe) == 0)
+			__r5l_stripe_write_finished(io);
+	}
+}
+
+static void r5l_do_submit_io(struct r5l_log *log, struct r5l_io_unit *io)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&log->io_list_lock, flags);
+	__r5l_set_io_unit_state(io, IO_UNIT_IO_START);
+	spin_unlock_irqrestore(&log->io_list_lock, flags);
+
+	if (io->has_flush)
+		bio_set_op_attrs(io->current_bio, REQ_OP_WRITE, WRITE_FLUSH);
+	if (io->has_fua)
+		bio_set_op_attrs(io->current_bio, REQ_OP_WRITE, WRITE_FUA);
+	submit_bio(io->current_bio);
+
+	if (!io->split_bio)
+		return;
+
+	if (io->has_flush)
+		bio_set_op_attrs(io->split_bio, REQ_OP_WRITE, WRITE_FLUSH);
+	if (io->has_fua)
+		bio_set_op_attrs(io->split_bio, REQ_OP_WRITE, WRITE_FUA);
+	submit_bio(io->split_bio);
+}
+
+/* deferred io_unit will be dispatched here */
+static void r5l_submit_io_async(struct work_struct *work)
+{
+	struct r5l_log *log = container_of(work, struct r5l_log,
+					   deferred_io_work);
+	struct r5l_io_unit *io = NULL;
+	unsigned long flags;
+
+	spin_lock_irqsave(&log->io_list_lock, flags);
+	if (!list_empty(&log->running_ios)) {
+		io = list_first_entry(&log->running_ios, struct r5l_io_unit,
+				      log_sibling);
+		if (!io->io_deferred)
+			io = NULL;
+		else
+			io->io_deferred = 0;
+	}
+	spin_unlock_irqrestore(&log->io_list_lock, flags);
+	if (io)
+		r5l_do_submit_io(log, io);
 }
 
 static void r5l_submit_current_io(struct r5l_log *log)
 {
 	struct r5l_io_unit *io = log->current_io;
+	struct bio *bio;
 	struct r5l_meta_block *block;
 	unsigned long flags;
 	u32 crc;
+	bool do_submit = true;
 
 	if (!io)
 		return;
@@ -519,13 +608,20 @@ static void r5l_submit_current_io(struct r5l_log *log)
 	block->meta_size = cpu_to_le32(io->meta_offset);
 	crc = crc32c_le(log->uuid_checksum, block, PAGE_SIZE);
 	block->checksum = cpu_to_le32(crc);
+	bio = io->current_bio;
 
 	log->current_io = NULL;
 	spin_lock_irqsave(&log->io_list_lock, flags);
-	__r5l_set_io_unit_state(io, IO_UNIT_IO_START);
+	if (io->has_flush || io->has_fua) {
+		if (io != list_first_entry(&log->running_ios,
+					   struct r5l_io_unit, log_sibling)) {
+			io->io_deferred = 1;
+			do_submit = false;
+		}
+	}
 	spin_unlock_irqrestore(&log->io_list_lock, flags);
-
-	submit_bio(io->current_bio);
+	if (do_submit)
+		r5l_do_submit_io(log, io);
 }
 
 static struct bio *r5l_bio_alloc(struct r5l_log *log)
@@ -570,6 +666,7 @@ static struct r5l_io_unit *r5l_new_meta(struct r5l_log *log)
 	io->log = log;
 	INIT_LIST_HEAD(&io->log_sibling);
 	INIT_LIST_HEAD(&io->stripe_list);
+	bio_list_init(&io->flush_barriers);
 	io->state = IO_UNIT_RUNNING;
 
 	io->meta_page = mempool_alloc(log->meta_pool, GFP_NOIO);
@@ -640,12 +737,11 @@ static void r5l_append_payload_page(struct r5l_log *log, struct page *page)
 	struct r5l_io_unit *io = log->current_io;
 
 	if (io->need_split_bio) {
-		struct bio *prev = io->current_bio;
-
+		BUG_ON(io->split_bio);
+		io->split_bio = io->current_bio;
 		io->current_bio = r5l_bio_alloc(log);
-		bio_chain(io->current_bio, prev);
-
-		submit_bio(prev);
+		bio_chain(io->current_bio, io->split_bio);
+		io->need_split_bio = false;
 	}
 
 	if (!bio_add_page(io->current_bio, page, PAGE_SIZE, 0))
@@ -675,12 +771,23 @@ static int r5l_log_stripe(struct r5l_log *log, struct stripe_head *sh,
 
 	io = log->current_io;
 
+	if (test_and_clear_bit(STRIPE_R5C_PREFLUSH, &sh->state))
+		io->has_flush = 1;
+
 	for (i = 0; i < sh->disks; i++) {
 		if (!test_bit(R5_Wantwrite, &sh->dev[i].flags) &&
 		    !test_bit(R5_Wantcache, &sh->dev[i].flags))
 			continue;
 		if (i == sh->pd_idx || i == sh->qd_idx)
 			continue;
+		if (test_bit(R5_WantFUA, &sh->dev[i].flags)) {
+			io->has_fua = 1;
+			/*
+			 * we need to flush journal to make sure recovery can
+			 * reach the data with fua flag
+			 */
+			io->has_flush = 1;
+		}
 		r5l_append_payload_meta(log, R5LOG_PAYLOAD_DATA,
 					raid5_compute_blocknr(sh, i, 0),
 					sh->dev[i].log_checksum, 0, false);
@@ -845,17 +952,34 @@ int r5l_handle_flush_request(struct r5l_log *log, struct bio *bio)
 {
 	if (!log)
 		return -ENODEV;
-	/*
-	 * we flush log disk cache first, then write stripe data to raid disks.
-	 * So if bio is finished, the log disk cache is flushed already. The
-	 * recovery guarantees we can recovery the bio from log disk, so we
-	 * don't need to flush again
-	 */
-	if (bio->bi_iter.bi_size == 0) {
-		bio_endio(bio);
-		return 0;
+
+	if (log->r5c_state == R5C_STATE_WRITE_THROUGH) {
+		/*
+		 * in write through (journal only)
+		 * we flush log disk cache first, then write stripe data to
+		 * raid disks. So if bio is finished, the log disk cache is
+		 * flushed already. The recovery guarantees we can recovery
+		 * the bio from log disk, so we don't need to flush again
+		 */
+		if (bio->bi_iter.bi_size == 0) {
+			bio_endio(bio);
+			return 0;
+		}
+		bio->bi_opf &= ~REQ_PREFLUSH;
+	} else {
+		/* write back (with cache) */
+		if (bio->bi_iter.bi_size == 0) {
+			mutex_lock(&log->io_mutex);
+			r5l_get_meta(log, 0);
+			bio_list_add(&log->current_io->flush_barriers, bio);
+			log->current_io->has_flush = 1;
+			log->current_io->has_null_flush = 1;
+			atomic_inc(&log->current_io->pending_stripe);
+			r5l_submit_current_io(log);
+			mutex_unlock(&log->io_mutex);
+			return 0;
+		}
 	}
-	bio->bi_opf &= ~REQ_PREFLUSH;
 	return -EAGAIN;
 }
 
@@ -2314,6 +2438,8 @@ int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
 	INIT_LIST_HEAD(&log->no_space_stripes);
 	spin_lock_init(&log->no_space_stripes_lock);
 
+	INIT_WORK(&log->deferred_io_work, r5l_submit_io_async);
+
 	log->r5c_state = R5C_STATE_WRITE_THROUGH;
 	INIT_LIST_HEAD(&log->stripe_in_cache_list);
 	spin_lock_init(&log->stripe_in_cache_lock);
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index ffabde9..cb81703 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5224,6 +5224,7 @@ static void raid5_make_request(struct mddev *mddev, struct bio * bi)
 	int remaining;
 	DEFINE_WAIT(w);
 	bool do_prepare;
+	bool do_flush = false;
 
 	if (unlikely(bi->bi_opf & REQ_PREFLUSH)) {
 		int ret = r5l_handle_flush_request(conf->log, bi);
@@ -5235,6 +5236,7 @@ static void raid5_make_request(struct mddev *mddev, struct bio * bi)
 			return;
 		}
 		/* ret == -EAGAIN, fallback */
+		do_flush = true;
 	}
 
 	md_write_start(mddev, bi);
@@ -5374,6 +5376,12 @@ static void raid5_make_request(struct mddev *mddev, struct bio * bi)
 				do_prepare = true;
 				goto retry;
 			}
+			if (do_flush) {
+				set_bit(STRIPE_R5C_PREFLUSH, &sh->state);
+				/* we only need flush for one stripe */
+				do_flush = false;
+			}
+
 			set_bit(STRIPE_HANDLE, &sh->state);
 			clear_bit(STRIPE_DELAYED, &sh->state);
 			if ((!sh->batch_head || sh == sh->batch_head) &&
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 6898a76..317f204 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -360,6 +360,7 @@ enum {
 	STRIPE_R5C_FULL_STRIPE,	/* in r5c cache (to-be/being handled or
 				 * in conf->r5c_full_stripe_list)
 				 */
+	STRIPE_R5C_PREFLUSH,	/* need to flush journal device */
 };
 
 #define STRIPE_EXPAND_SYNC_FLAGS \
-- 
2.9.3

Re: [PATCH v4 5/8] md/r5cache: reclaim support

[Shaohua Li]

On Mon, Oct 10, 2016 at 05:24:43PM -0700, Song Liu wrote:
> There are two limited resources, stripe cache and journal disk space.
> For better performance, we priotize reclaim of full stripe writes.
> To free up more journal space, we free earliest data on the journal.
> 
> In current implementation, reclaim happens when:
> 1. every R5C_RECLAIM_WAKEUP_INTERVAL (5 seconds)

This is the protection. If no reclaim runs in last 5 seconds, trigger this.
Otherwise, don't do this.

> 2. when there are R5C_FULL_STRIPE_FLUSH_BATCH (8) cached full stripes
>    (r5c_check_cached_full_stripe)

8 stripes aren't big. I'd use 128k so 32 strieps. 128k size IO should be good
for harddisk.

I'd suggest something like this:

1. if no stripe cache pressure and there are 32+ full stripes, flush all full
stripes
2. if stripe cache pressure is moderate, flush all full stripes

3. if stripe cache pressure is high, flush all full stripes first. If pressure
is still higher than a watermark, flush partial full stripes.

The principle is to flush full stripes if possible and flush as more as
possible. reclaim will do disk cache flush and so is an expensive operation.

> 3. when raid5_get_active_stripe sees pressure in stripe cache space
>    (r5c_check_stripe_cache_usage)
> 4. when there is pressure in journal space.
> 
> 1-3 above are straightforward. The following explains details of 4.
> 
> To avoid deadlock due to log space, we need to reserve enough space
> to flush cached data. The size of required log space depends on total
> number of cached stripes (stripe_in_cache_count). In current
> implementation, the reclaim path automatically include pending
> data writes with parity writes (similar to write through case).
> Therefore, we need up to (conf->raid_disks + 1) pages for each cached
> stripe (1 page for meta data, raid_disks pages for all data and
> parity). r5c_log_required_to_flush_cache() calculates log space
> required to flush cache. In the following, we refer to the space
> calculated by r5c_log_required_to_flush_cache() as
> reclaim_required_space.
> 
> Two flags are added to r5conf->cache_state: R5C_LOG_TIGHT and
> R5C_LOG_CRITICAL. R5C_LOG_TIGHT is set when free space on the log
> device is less than 3x of reclaim_required_space. R5C_LOG_CRITICAL
> is set when free space on the log device is less than 2x of
> reclaim_required_space.
> 
> r5c_cache keeps all data in cache (not fully committed to RAID) in
> a list (stripe_in_cache_list). These stripes are in the order of their
> first appearance on the journal. So the log tail (last_checkpoint)
> should point to the journal_start of the first item in the list.
> 
> When R5C_LOG_TIGHT is set, r5l_reclaim_thread starts flushing out
> stripes at the head of stripe_in_cache. When R5C_LOG_CRITICAL is
> set, the state machine only writes data that are already in the
> log device (in stripe_in_cache_list).
> 
> Signed-off-by: Song Liu <songliubraving@fb.com>
> ---
>  drivers/md/raid5-cache.c | 363 +++++++++++++++++++++++++++++++++++++++++++----
>  drivers/md/raid5.c       |  17 +++
>  drivers/md/raid5.h       |  39 +++--
>  3 files changed, 383 insertions(+), 36 deletions(-)
> 
> diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
> index 92d3d7b..2774f93 100644
> --- a/drivers/md/raid5-cache.c
> +++ b/drivers/md/raid5-cache.c
> @@ -29,12 +29,21 @@
>  #define BLOCK_SECTORS (8)
>  
>  /*
> - * reclaim runs every 1/4 disk size or 10G reclaimable space. This can prevent
> - * recovery scans a very long log
> + * log->max_free_space is min(1/4 disk size, 10G reclaimable space).
> + *
> + * In write through mode, the reclaim runs every log->max_free_space.
> + * This can prevent the recovery scans for too long
>   */
>  #define RECLAIM_MAX_FREE_SPACE (10 * 1024 * 1024 * 2) /* sector */
>  #define RECLAIM_MAX_FREE_SPACE_SHIFT (2)
>  
> +/* wake up reclaim thread periodically */
> +#define R5C_RECLAIM_WAKEUP_INTERVAL (5 * HZ)
> +/* start flush with these full stripes */
> +#define R5C_FULL_STRIPE_FLUSH_BATCH 8
> +/* reclaim stripes in groups */
> +#define R5C_RECLAIM_STRIPE_GROUP (NR_STRIPE_HASH_LOCKS * 2)
> +
>  /*
>   * We only need 2 bios per I/O unit to make progress, but ensure we
>   * have a few more available to not get too tight.
> @@ -141,6 +150,11 @@ struct r5l_log {
>  
>  	/* for r5c_cache */
>  	enum r5c_state r5c_state;
> +	struct list_head stripe_in_cache_list;	/* all stripes in r5cache, with
> +						 * sh->log_start in order
> +						 */

The comment isn't correct. log_start could wrap. The stripes are actually
ordered in seq. Please move the comments above stripe_in_cache_list.

> +/*
> + * r5c_flush_stripe moves stripe from cached list to handle_list. When called,
> + * the stripe must be on r5c_cached_full_stripes or r5c_cached_partial_stripes.
> + *
> + * must hold conf->device_lock
> + */
> +static void r5c_flush_stripe(struct r5conf *conf, struct stripe_head *sh)
> +{
> +	BUG_ON(list_empty(&sh->lru));
> +	BUG_ON(test_bit(STRIPE_R5C_FROZEN, &sh->state));
> +	BUG_ON(test_bit(STRIPE_HANDLE, &sh->state));
> +	assert_spin_locked(&conf->device_lock);
> +
> +	list_del_init(&sh->lru);
> +	atomic_inc(&sh->count);
> +
> +	set_bit(STRIPE_HANDLE, &sh->state);
> +	atomic_inc(&conf->active_stripes);
> +	r5c_freeze_stripe_for_reclaim(sh);
> +
> +	set_bit(STRIPE_PREREAD_ACTIVE, &sh->state);

we increase preread_active_stripes too if the STRIPE_PREREAD_ACTIVE isn't set.
Why not here?

Thanks,
Shaohua

Re: [PATCH v4 6/8] md/r5cache: sysfs entry r5c_state

[Shaohua Li]

On Mon, Oct 10, 2016 at 05:24:44PM -0700, Song Liu wrote:
> r5c_state have 4 states:
> * no-cache;
> * write-through (write journal only);
> * write-back (w/ write cache);
> * cache-broken (journal missing or Faulty)
> 
> When there is functional write cache, r5c_state is a knob to
> switch between write-back and write-through.
> 
> When the journal device is broken, the raid array is forced
> in readonly mode. In this case, r5c_state can be used to
> remove "journal feature", and thus make the array read-write
> without journal. By writing into r5c_cache_mode, the array
> can transit from cache-broken to no-cache, which removes
> journal feature for the array.
> 
> To remove the journal feature:
> - When journal fails, the raid array is forced readonly mode
>   (enforced by kernel)
> - User uses the new interface to remove journal (writing 0
>   to r5c_state, I will add a mdadm option for that later)
> - User forces array read-write;
> - Kernel updates superblock and array can run read/write.
> 
> Signed-off-by: Song Liu <songliubraving@fb.com>
> ---
>  drivers/md/raid5-cache.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++
>  drivers/md/raid5.c       |  1 +
>  drivers/md/raid5.h       |  1 +
>  3 files changed, 60 insertions(+)
> 
> diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
> index 2774f93..b19024c 100644
> --- a/drivers/md/raid5-cache.c
> +++ b/drivers/md/raid5-cache.c
> @@ -57,6 +57,8 @@ enum r5c_state {
>  	R5C_STATE_CACHE_BROKEN = 3,
>  };
>  
> +static char *r5c_state_str[] = {"no-cache", "write-through",
> +				"write-back", "cache-broken"};
>  /*
>   * raid5 cache state machine
>   *
> @@ -1519,6 +1521,62 @@ int r5c_flush_cache(struct r5conf *conf, int num)
>  	return count;
>  }
>  
> +ssize_t r5c_state_show(struct mddev *mddev, char *page)
> +{
> +	struct r5conf *conf = mddev->private;
> +	int val = 0;
> +	int ret = 0;
> +
> +	if (conf->log)
> +		val = conf->log->r5c_state;
> +	else if (test_bit(MD_HAS_JOURNAL, &mddev->flags))
> +		val = R5C_STATE_CACHE_BROKEN;
> +	ret += snprintf(page, PAGE_SIZE - ret, "%d: %s\n",
> +			val, r5c_state_str[val]);
No point to do PAGE_SIZE - ret

This isn't how sysfs entry is supposed to output. You can either show the value
or the string, not both with format. I'd prefer the string though, and make
store accept string.

Thanks,
Shaohua

Re: [PATCH v4 0/8] raid5-cache: enabling cache features

[Shaohua Li]

On Mon, Oct 10, 2016 at 05:24:38PM -0700, Song Liu wrote:
> These are the 4th version of patches to enable write cache part of
> raid5-cache. The journal part was released with kernel 4.4.
> 
> The caching part uses same disk format of raid456 journal, and provides
> acceleration to writes. Write operations are committed (bio_endio) once
> the data is secured in journal. Reconstruct and RMW are postponed to
> reclaim path, which is (hopefully) not on the critical path.
> 
> The changes are organized in 8 patches (details below).
> 
> Patch for chunk_aligned_read in earlier RFC is not included yet
> (http://marc.info/?l=linux-raid&m=146432700719277). But we may still need
> some optimizations later, especially for SSD raid devices.
> 
> Changes from PATCH v3 (http://marc.info/?l=linux-raid&m=147573807306070):
>   1. Make reclaim robust
>   2. Fix a bug in recovery
> 
> Changes between v3 and v2 (http://marc.info/?l=linux-raid&m=147493266208102):
>   1. Incorporate feedback from Shaohua
>   2. Reorganize the patches, for hopefully easier review
>   3. Make sure no change to write through mode (journal only)
>   4. Change reclaim design to avoid deadlock due to log space

Could you please add a test case for this in mdadm test suites?

Thanks,
Shaohua

Re: [PATCH v4 6/8] md/r5cache: sysfs entry r5c_state

[Song Liu]

> On Oct 12, 2016, at 9:56 AM, Shaohua Li <shli@kernel.org> wrote:
> 
>> 
> 
> This isn't how sysfs entry is supposed to output. You can either show the value
> or the string, not both with format. I'd prefer the string though, and make
> store accept string.

I implemented something like the following:

root@virt-test:~/md# cat /sys/block/md0/md/r5c_state
[write-through] write-back
root@virt-test:~/md# echo write-back > /sys/block/md0/md/r5c_state
root@virt-test:~/md# cat /sys/block/md0/md/r5c_state
write-through [write-back]

root@virt-test:~/md# ./mdadm --fail /dev/md0 /dev/loop4
mdadm: set /dev/loop4 faulty in /dev/md0
root@virt-test:~/md# cat /sys/block/md0/md/r5c_state
no-cache [cache-broken]
root@virt-test:~/md# echo no-cache > /sys/block/md0/md/r5c_state
root@virt-test:~/md# cat /sys/block/md0/md/r5c_state
no-cache

It will be part of next version. 

Thanks,
Song