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/Makefile b/drivers/md/Makefile
index 3cbda1a..4d48714 100644
--- a/drivers/md/Makefile
+++ b/drivers/md/Makefile
@@ -18,7 +18,7 @@
dm-era-y += dm-era-target.o
dm-verity-y += dm-verity-target.o
md-mod-y += md.o bitmap.o
-raid456-y += raid5.o raid5-cache.o
+raid456-y += raid5.o raid5-cache.o raid5-ppl.o
# Note: link order is important. All raid personalities
# and must come before md.o, as they each initialise
