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

Pull MD updates from Shaohua Li:

 - Add Partial Parity Log (ppl) feature found in Intel IMSM raid array
   by Artur Paszkiewicz. This feature is another way to close RAID5
   writehole. The Linux implementation is also available for normal
   RAID5 array if specific superblock bit is set.

 - A number of md-cluser fixes and enabling md-cluster array resize from
   Guoqing Jiang

 - A bunch of patches from Ming Lei and Neil Brown to rewrite MD bio
   handling related code. Now MD doesn't directly access bio bvec,
   bi_phys_segments and uses modern bio API for bio split.

 - Improve RAID5 IO pattern to improve performance for hard disk based
   RAID5/6 from me.

 - Several patches from Song Liu to speed up raid5-cache recovery and
   allow raid5 cache feature disabling in runtime.

 - Fix a performance regression in raid1 resync from Xiao Ni.

 - Other cleanup and fixes from various people.

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/shli/md: (84 commits)
  md/raid10: skip spare disk as 'first' disk
  md/raid1: Use a new variable to count flighting sync requests
  md: clear WantReplacement once disk is removed
  md/raid1/10: remove unused queue
  md: handle read-only member devices better.
  md/raid10: wait up frozen array in handle_write_completed
  uapi: fix linux/raid/md_p.h userspace compilation error
  md-cluster: Fix a memleak in an error handling path
  md: support disabling of create-on-open semantics.
  md: allow creation of mdNNN arrays via md_mod/parameters/new_array
  raid5-ppl: use a single mempool for ppl_io_unit and header_page
  md/raid0: fix up bio splitting.
  md/linear: improve bio splitting.
  md/raid5: make chunk_aligned_read() split bios more cleanly.
  md/raid10: simplify handle_read_error()
  md/raid10: simplify the splitting of requests.
  md/raid1: factor out flush_bio_list()
  md/raid1: simplify handle_read_error().
  Revert "block: introduce bio_copy_data_partial"
  md/raid1: simplify alloc_behind_master_bio()
  ...

3 files changed, 74 insertions, 4 deletions

diff --git a/Documentation/admin-guide/md.rst b/Documentation/admin-guide/md.rst
index 1e61bf50595c..84de718f24a4 100644
--- a/Documentation/admin-guide/md.rst
+++ b/Documentation/admin-guide/md.rst
@@ -276,14 +276,14 @@ All md devices contain:
      array creation it will default to 0, though starting the array as
      ``clean`` will set it much larger.
 
-   new_dev
+  new_dev
      This file can be written but not read.  The value written should
      be a block device number as major:minor.  e.g. 8:0
      This will cause that device to be attached to the array, if it is
      available.  It will then appear at md/dev-XXX (depending on the
      name of the device) and further configuration is then possible.
 
-   safe_mode_delay
+  safe_mode_delay
      When an md array has seen no write requests for a certain period
      of time, it will be marked as ``clean``.  When another write
      request arrives, the array is marked as ``dirty`` before the write
@@ -292,7 +292,7 @@ All md devices contain:
      period as a number of seconds.  The default is 200msec (0.200).
      Writing a value of 0 disables safemode.
 
-   array_state
+  array_state
      This file contains a single word which describes the current
      state of the array.  In many cases, the state can be set by
      writing the word for the desired state, however some states
@@ -401,7 +401,30 @@ All md devices contain:
      once the array becomes non-degraded, and this fact has been
      recorded in the metadata.
 
+  consistency_policy
+     This indicates how the array maintains consistency in case of unexpected
+     shutdown. It can be:
 
+     none
+       Array has no redundancy information, e.g. raid0, linear.
+
+     resync
+       Full resync is performed and all redundancy is regenerated when the
+       array is started after unclean shutdown.
+
+     bitmap
+       Resync assisted by a write-intent bitmap.
+
+     journal
+       For raid4/5/6, journal device is used to log transactions and replay
+       after unclean shutdown.
+
+     ppl
+       For raid5 only, Partial Parity Log is used to close the write hole and
+       eliminate resync.
+
+     The accepted values when writing to this file are ``ppl`` and ``resync``,
+     used to enable and disable PPL.
 
 
 As component devices are added to an md array, they appear in the ``md``
@@ -563,6 +586,9 @@ Each directory contains:
 	adds bad blocks without acknowledging them. This is largely
 	for testing.
 
+      ppl_sector, ppl_size
+        Location and size (in sectors) of the space used for Partial Parity Log
+        on this device.
 
 
 An active md device will also contain an entry for each active device
diff --git a/Documentation/md/md-cluster.txt b/Documentation/md/md-cluster.txt
index d22103994aef..82ee51604e9a 100644
--- a/Documentation/md/md-cluster.txt
+++ b/Documentation/md/md-cluster.txt
@@ -321,4 +321,4 @@ The algorithm is:
 
 There are somethings which are not supported by cluster MD yet.
 
-- update size and change array_sectors.
+- change array_sectors.
diff --git a/Documentation/md/raid5-ppl.txt b/Documentation/md/raid5-ppl.txt
new file mode 100644
index 000000000000..127072b09363
--- /dev/null
+++ b/Documentation/md/raid5-ppl.txt
@@ -0,0 +1,44 @@
+Partial Parity Log
+
+Partial Parity Log (PPL) is a feature available for RAID5 arrays. The issue
+addressed by PPL is that after a dirty shutdown, parity of a particular stripe
+may become inconsistent with data on other member disks. If the array is also
+in degraded state, there is no way to recalculate parity, because one of the
+disks is missing. This can lead to silent data corruption when rebuilding the
+array or using it is as degraded - data calculated from parity for array blocks
+that have not been touched by a write request during the unclean shutdown can
+be incorrect. Such condition is known as the RAID5 Write Hole. Because of
+this, md by default does not allow starting a dirty degraded array.
+
+Partial parity for a write operation is the XOR of stripe data chunks not
+modified by this write. It is just enough data needed for recovering from the
+write hole. XORing partial parity with the modified chunks produces parity for
+the stripe, consistent with its state before the write operation, regardless of
+which chunk writes have completed. If one of the not modified data disks of
+this stripe is missing, this updated parity can be used to recover its
+contents. PPL recovery is also performed when starting an array after an
+unclean shutdown and all disks are available, eliminating the need to resync
+the array. Because of this, using write-intent bitmap and PPL together is not
+supported.
+
+When handling a write request PPL writes partial parity before new data and
+parity are dispatched to disks. PPL is a distributed log - it is stored on
+array member drives in the metadata area, on the parity drive of a particular
+stripe.  It does not require a dedicated journaling drive. Write performance is
+reduced by up to 30%-40% but it scales with the number of drives in the array
+and the journaling drive does not become a bottleneck or a single point of
+failure.
+
+Unlike raid5-cache, the other solution in md for closing the write hole, PPL is
+not a true journal. It does not protect from losing in-flight data, only from
+silent data corruption. If a dirty disk of a stripe is lost, no PPL recovery is
+performed for this stripe (parity is not updated). So it is possible to have
+arbitrary data in the written part of a stripe if that disk is lost. In such
+case the behavior is the same as in plain raid5.
+
+PPL is available for md version-1 metadata and external (specifically IMSM)
+metadata arrays. It can be enabled using mdadm option --consistency-policy=ppl.
+
+Currently, volatile write-back cache should be disabled on all member drives
+when using PPL. Otherwise it cannot guarantee consistency in case of power
+failure.