Merge tag 'for-4.19/block-20180812' of git://git.kernel.dk/linux-block

Pull block updates from Jens Axboe:
 "First pull request for this merge window, there will also be a
  followup request with some stragglers.

  This pull request contains:

   - Fix for a thundering heard issue in the wbt block code (Anchal
     Agarwal)

   - A few NVMe pull requests:
      * Improved tracepoints (Keith)
      * Larger inline data support for RDMA (Steve Wise)
      * RDMA setup/teardown fixes (Sagi)
      * Effects log suppor for NVMe target (Chaitanya Kulkarni)
      * Buffered IO suppor for NVMe target (Chaitanya Kulkarni)
      * TP4004 (ANA) support (Christoph)
      * Various NVMe fixes

   - Block io-latency controller support. Much needed support for
     properly containing block devices. (Josef)

   - Series improving how we handle sense information on the stack
     (Kees)

   - Lightnvm fixes and updates/improvements (Mathias/Javier et al)

   - Zoned device support for null_blk (Matias)

   - AIX partition fixes (Mauricio Faria de Oliveira)

   - DIF checksum code made generic (Max Gurtovoy)

   - Add support for discard in iostats (Michael Callahan / Tejun)

   - Set of updates for BFQ (Paolo)

   - Removal of async write support for bsg (Christoph)

   - Bio page dirtying and clone fixups (Christoph)

   - Set of bcache fix/changes (via Coly)

   - Series improving blk-mq queue setup/teardown speed (Ming)

   - Series improving merging performance on blk-mq (Ming)

   - Lots of other fixes and cleanups from a slew of folks"

* tag 'for-4.19/block-20180812' of git://git.kernel.dk/linux-block: (190 commits)
  blkcg: Make blkg_root_lookup() work for queues in bypass mode
  bcache: fix error setting writeback_rate through sysfs interface
  null_blk: add lock drop/acquire annotation
  Blk-throttle: reduce tail io latency when iops limit is enforced
  block: paride: pd: mark expected switch fall-throughs
  block: Ensure that a request queue is dissociated from the cgroup controller
  block: Introduce blk_exit_queue()
  blkcg: Introduce blkg_root_lookup()
  block: Remove two superfluous #include directives
  blk-mq: count the hctx as active before allocating tag
  block: bvec_nr_vecs() returns value for wrong slab
  bcache: trivial - remove tailing backslash in macro BTREE_FLAG
  bcache: make the pr_err statement used for ENOENT only in sysfs_attatch section
  bcache: set max writeback rate when I/O request is idle
  bcache: add code comments for bset.c
  bcache: fix mistaken comments in request.c
  bcache: fix mistaken code comments in bcache.h
  bcache: add a comment in super.c
  bcache: avoid unncessary cache prefetch bch_btree_node_get()
  bcache: display rate debug parameters to 0 when writeback is not running
  ...

1 files changed, 88 insertions, 4 deletions

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 8a2c52d5c53b..1746131bc9cb 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -51,6 +51,9 @@ v1 is available under Documentation/cgroup-v1/.
      5-3. IO
        5-3-1. IO Interface Files
        5-3-2. Writeback
+       5-3-3. IO Latency
+         5-3-3-1. How IO Latency Throttling Works
+         5-3-3-2. IO Latency Interface Files
      5-4. PID
        5-4-1. PID Interface Files
      5-5. Device
@@ -1314,17 +1317,19 @@ IO Interface Files
 	Lines are keyed by $MAJ:$MIN device numbers and not ordered.
 	The following nested keys are defined.
 
-	  ======	===================
+	  ======	=====================
 	  rbytes	Bytes read
 	  wbytes	Bytes written
 	  rios		Number of read IOs
 	  wios		Number of write IOs
-	  ======	===================
+	  dbytes	Bytes discarded
+	  dios		Number of discard IOs
+	  ======	=====================
 
 	An example read output follows:
 
-	  8:16 rbytes=1459200 wbytes=314773504 rios=192 wios=353
-	  8:0 rbytes=90430464 wbytes=299008000 rios=8950 wios=1252
+	  8:16 rbytes=1459200 wbytes=314773504 rios=192 wios=353 dbytes=0 dios=0
+	  8:0 rbytes=90430464 wbytes=299008000 rios=8950 wios=1252 dbytes=50331648 dios=3021
 
   io.weight
 	A read-write flat-keyed file which exists on non-root cgroups.
@@ -1446,6 +1451,85 @@ writeback as follows.
 	vm.dirty[_background]_ratio.
 
 
+IO Latency
+~~~~~~~~~~
+
+This is a cgroup v2 controller for IO workload protection.  You provide a group
+with a latency target, and if the average latency exceeds that target the
+controller will throttle any peers that have a lower latency target than the
+protected workload.
+
+The limits are only applied at the peer level in the hierarchy.  This means that
+in the diagram below, only groups A, B, and C will influence each other, and
+groups D and F will influence each other.  Group G will influence nobody.
+
+			[root]
+		/	   |		\
+		A	   B		C
+	       /  \        |
+	      D    F	   G
+
+
+So the ideal way to configure this is to set io.latency in groups A, B, and C.
+Generally you do not want to set a value lower than the latency your device
+supports.  Experiment to find the value that works best for your workload.
+Start at higher than the expected latency for your device and watch the
+avg_lat value in io.stat for your workload group to get an idea of the
+latency you see during normal operation.  Use the avg_lat value as a basis for
+your real setting, setting at 10-15% higher than the value in io.stat.
+
+How IO Latency Throttling Works
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+io.latency is work conserving; so as long as everybody is meeting their latency
+target the controller doesn't do anything.  Once a group starts missing its
+target it begins throttling any peer group that has a higher target than itself.
+This throttling takes 2 forms:
+
+- Queue depth throttling.  This is the number of outstanding IO's a group is
+  allowed to have.  We will clamp down relatively quickly, starting at no limit
+  and going all the way down to 1 IO at a time.
+
+- Artificial delay induction.  There are certain types of IO that cannot be
+  throttled without possibly adversely affecting higher priority groups.  This
+  includes swapping and metadata IO.  These types of IO are allowed to occur
+  normally, however they are "charged" to the originating group.  If the
+  originating group is being throttled you will see the use_delay and delay
+  fields in io.stat increase.  The delay value is how many microseconds that are
+  being added to any process that runs in this group.  Because this number can
+  grow quite large if there is a lot of swapping or metadata IO occurring we
+  limit the individual delay events to 1 second at a time.
+
+Once the victimized group starts meeting its latency target again it will start
+unthrottling any peer groups that were throttled previously.  If the victimized
+group simply stops doing IO the global counter will unthrottle appropriately.
+
+IO Latency Interface Files
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+  io.latency
+	This takes a similar format as the other controllers.
+
+		"MAJOR:MINOR target=<target time in microseconds"
+
+  io.stat
+	If the controller is enabled you will see extra stats in io.stat in
+	addition to the normal ones.
+
+	  depth
+		This is the current queue depth for the group.
+
+	  avg_lat
+		This is an exponential moving average with a decay rate of 1/exp
+		bound by the sampling interval.  The decay rate interval can be
+		calculated by multiplying the win value in io.stat by the
+		corresponding number of samples based on the win value.
+
+	  win
+		The sampling window size in milliseconds.  This is the minimum
+		duration of time between evaluation events.  Windows only elapse
+		with IO activity.  Idle periods extend the most recent window.
+
 PID
 ---