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>
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 6dd295a..ba5b7a3 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -224,10 +224,16 @@ struct stripe_head {
spinlock_t batch_lock; /* only header's lock is useful */
struct list_head batch_list; /* protected by head's batch lock*/
- struct r5l_io_unit *log_io;
+ union {
+ struct r5l_io_unit *log_io;
+ struct ppl_io_unit *ppl_io;
+ };
+
struct list_head log_list;
sector_t log_start; /* first meta block on the journal */
struct list_head r5c; /* for r5c_cache->stripe_in_journal */
+
+ struct page *ppl_page; /* partial parity of this stripe */
/**
* struct stripe_operations
* @target - STRIPE_OP_COMPUTE_BLK target
@@ -400,6 +406,7 @@ enum {
STRIPE_OP_BIODRAIN,
STRIPE_OP_RECONSTRUCT,
STRIPE_OP_CHECK,
+ STRIPE_OP_PARTIAL_PARITY,
};
/*
@@ -696,6 +703,7 @@ struct r5conf {
int group_cnt;
int worker_cnt_per_group;
struct r5l_log *log;
+ void *log_private;
spinlock_t pending_bios_lock;
bool batch_bio_dispatch;