raid5-ppl: Partial Parity Log write logging implementation

Implement the calculation of partial parity for a stripe and PPL write
logging functionality. The description of PPL is added to the
documentation. More details can be found in the comments in raid5-ppl.c.

Attach a page for holding the partial parity data to stripe_head.
Allocate it only if mddev has the MD_HAS_PPL flag set.

Partial parity is the xor of not modified data chunks of a stripe and is
calculated as follows:

- reconstruct-write case:
  xor data from all not updated disks in a stripe

- read-modify-write case:
  xor old data and parity from all updated disks in a stripe

Implement it using the async_tx API and integrate into raid_run_ops().
It must be called when we still have access to old data, so do it when
STRIPE_OP_BIODRAIN is set, but before ops_run_prexor5(). The result is
stored into sh->ppl_page.

Partial parity is not meaningful for full stripe write and is not stored
in the log or used for recovery, so don't attempt to calculate it when
stripe has STRIPE_FULL_WRITE.

Put the PPL metadata structures to md_p.h because userspace tools
(mdadm) will also need to read/write PPL.

Warn about using PPL with enabled disk volatile write-back cache for
now. It can be removed once disk cache flushing before writing PPL is
implemented.

Signed-off-by: Artur Paszkiewicz <artur.paszkiewicz@intel.com>
Signed-off-by: Shaohua Li <shli@fb.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/drivers/md/raid5-log.h b/drivers/md/raid5-log.h
index 2da4bd3bbd79..a67fb58513b9 100644
--- a/drivers/md/raid5-log.h
+++ b/drivers/md/raid5-log.h
@@ -31,6 +31,20 @@ extern struct md_sysfs_entry r5c_journal_mode;
 extern void r5c_update_on_rdev_error(struct mddev *mddev);
 extern bool r5c_big_stripe_cached(struct r5conf *conf, sector_t sect);
 
+extern struct dma_async_tx_descriptor *
+ops_run_partial_parity(struct stripe_head *sh, struct raid5_percpu *percpu,
+		       struct dma_async_tx_descriptor *tx);
+extern int ppl_init_log(struct r5conf *conf);
+extern void ppl_exit_log(struct r5conf *conf);
+extern int ppl_write_stripe(struct r5conf *conf, struct stripe_head *sh);
+extern void ppl_write_stripe_run(struct r5conf *conf);
+extern void ppl_stripe_write_finished(struct stripe_head *sh);
+
+static inline bool raid5_has_ppl(struct r5conf *conf)
+{
+	return test_bit(MD_HAS_PPL, &conf->mddev->flags);
+}
+
 static inline int log_stripe(struct stripe_head *sh, struct stripe_head_state *s)
 {
 	struct r5conf *conf = sh->raid_conf;
@@ -45,6 +59,8 @@ static inline int log_stripe(struct stripe_head *sh, struct stripe_head_state *s
 			/* caching phase */
 			return r5c_cache_data(conf->log, sh);
 		}
+	} else if (raid5_has_ppl(conf)) {
+		return ppl_write_stripe(conf, sh);
 	}
 
 	return -EAGAIN;
@@ -56,24 +72,32 @@ static inline void log_stripe_write_finished(struct stripe_head *sh)
 
 	if (conf->log)
 		r5l_stripe_write_finished(sh);
+	else if (raid5_has_ppl(conf))
+		ppl_stripe_write_finished(sh);
 }
 
 static inline void log_write_stripe_run(struct r5conf *conf)
 {
 	if (conf->log)
 		r5l_write_stripe_run(conf->log);
+	else if (raid5_has_ppl(conf))
+		ppl_write_stripe_run(conf);
 }
 
 static inline void log_exit(struct r5conf *conf)
 {
 	if (conf->log)
 		r5l_exit_log(conf);
+	else if (raid5_has_ppl(conf))
+		ppl_exit_log(conf);
 }
 
 static inline int log_init(struct r5conf *conf, struct md_rdev *journal_dev)
 {
 	if (journal_dev)
 		return r5l_init_log(conf, journal_dev);
+	else if (raid5_has_ppl(conf))
+		return ppl_init_log(conf);
 
 	return 0;
 }