svn commit: r354386 - vendor-sys/illumos/dist/uts/common/fs/zfs vendor-sys/illumos/dist/uts/common/fs/zfs/sys vendor-sys/illumos/dist/uts/common/sys/fs vendor/illumos/dist/cmd/zdb

Andriy Gapon avg at FreeBSD.org
Wed Nov 6 09:09:04 UTC 2019


Author: avg
Date: Wed Nov  6 09:09:03 2019
New Revision: 354386
URL: https://svnweb.freebsd.org/changeset/base/354386

Log:
  11770 additional mmp fixes
  
  illumos/illumos-gate at 4348eb901228d2f8fa50bb132a34248e8662074e
  https://github.com/illumos/illumos-gate/commit/4348eb901228d2f8fa50bb132a34248e8662074e
  
  https://www.illumos.org/issues/11770
    Port a few additional MMP fixes from ZoL that came in after our
    initial MMP port.
    4ca457b065 ZTS: Fix mmp_interval failure
    ca95f70dff zpool import progress kstat
    (only minimal changes from above can be pulled in right now)
    060f0226e6 MMP interval and fail_intervals in uberblock
  
  Portions contributed by: Jerry Jelinek <jerry.jelinek at joyent.com>
  Portions contributed by: Brian Behlendorf <behlendorf1 at llnl.gov>
  Author: Olaf Faaland <faaland1 at llnl.gov>

Modified:
  vendor-sys/illumos/dist/uts/common/fs/zfs/mmp.c
  vendor-sys/illumos/dist/uts/common/fs/zfs/spa.c
  vendor-sys/illumos/dist/uts/common/fs/zfs/sys/mmp.h
  vendor-sys/illumos/dist/uts/common/fs/zfs/sys/uberblock_impl.h
  vendor-sys/illumos/dist/uts/common/fs/zfs/uberblock.c
  vendor-sys/illumos/dist/uts/common/fs/zfs/vdev_label.c
  vendor-sys/illumos/dist/uts/common/sys/fs/zfs.h

Changes in other areas also in this revision:
Modified:
  vendor/illumos/dist/cmd/zdb/zdb.c

Modified: vendor-sys/illumos/dist/uts/common/fs/zfs/mmp.c
==============================================================================
--- vendor-sys/illumos/dist/uts/common/fs/zfs/mmp.c	Wed Nov  6 09:05:39 2019	(r354385)
+++ vendor-sys/illumos/dist/uts/common/fs/zfs/mmp.c	Wed Nov  6 09:09:03 2019	(r354386)
@@ -50,40 +50,101 @@
  * Uberblocks written by the txg_sync thread always go into the first
  * (N-MMP_BLOCKS_PER_LABEL) slots, the remaining slots are reserved for MMP.
  * They are used to hold uberblocks which are exactly the same as the last
- * synced uberblock except that the ub_timestamp is frequently updated.
- * Like all other uberblocks, the slot is written with an embedded checksum,
- * and slots with invalid checksums are ignored.  This provides the
+ * synced uberblock except that the ub_timestamp and mmp_config are frequently
+ * updated.  Like all other uberblocks, the slot is written with an embedded
+ * checksum, and slots with invalid checksums are ignored.  This provides the
  * "heartbeat", with no risk of overwriting good uberblocks that must be
  * preserved, e.g. previous txgs and associated block pointers.
  *
- * Two optional fields are added to uberblock structure: ub_mmp_magic and
- * ub_mmp_delay.  The magic field allows zfs to tell whether ub_mmp_delay is
- * valid.  The delay field is a decaying average of the amount of time between
- * completion of successive MMP writes, in nanoseconds.  It is used to predict
- * how long the import must wait to detect activity in the pool, before
- * concluding it is not in use.
+ * Three optional fields are added to uberblock structure; ub_mmp_magic,
+ * ub_mmp_config, and ub_mmp_delay.  The ub_mmp_magic value allows zfs to tell
+ * whether the other ub_mmp_* fields are valid.  The ub_mmp_config field tells
+ * the importing host the settings of zfs_multihost_interval and
+ * zfs_multihost_fail_intervals on the host which last had (or currently has)
+ * the pool imported.  These determine how long a host must wait to detect
+ * activity in the pool, before concluding the pool is not in use.  The
+ * mmp_delay field is a decaying average of the amount of time between
+ * completion of successive MMP writes, in nanoseconds.  It indicates whether
+ * MMP is enabled.
  *
  * During import an activity test may now be performed to determine if
  * the pool is in use.  The activity test is typically required if the
  * ZPOOL_CONFIG_HOSTID does not match the system hostid, the pool state is
  * POOL_STATE_ACTIVE, and the pool is not a root pool.
  *
- * The activity test finds the "best" uberblock (highest txg & timestamp),
- * waits some time, and then finds the "best" uberblock again.  If the txg
- * and timestamp in both "best" uberblocks do not match, the pool is in use
- * by another host and the import fails.  Since the granularity of the
- * timestamp is in seconds this activity test must take a bare minimum of one
- * second.  In order to assure the accuracy of the activity test, the default
- * values result in an activity test duration of 10x the mmp write interval.
+ * The activity test finds the "best" uberblock (highest txg, timestamp, and, if
+ * ub_mmp_magic is valid, sequence number from ub_mmp_config).  It then waits
+ * some time, and finds the "best" uberblock again.  If any of the mentioned
+ * fields have different values in the newly read uberblock, the pool is in use
+ * by another host and the import fails.  In order to assure the accuracy of the
+ * activity test, the default values result in an activity test duration of 20x
+ * the mmp write interval.
  *
- * The "zpool import"  activity test can be expected to take a minimum time of
- * zfs_multihost_import_intervals * zfs_multihost_interval milliseconds.  If the
- * "best" uberblock has a valid ub_mmp_delay field, then the duration of the
- * test may take longer if MMP writes were occurring less frequently than
- * expected.  Additionally, the duration is then extended by a random 25% to
- * attempt to to detect simultaneous imports.  For example, if both partner
- * hosts are rebooted at the same time and automatically attempt to import the
- * pool.
+ * The duration of the "zpool import" activity test depends on the information
+ * available in the "best" uberblock:
+ *
+ * 1) If uberblock was written by zfs-0.8 or newer and fail_intervals > 0:
+ *    ub_mmp_config.fail_intervals * ub_mmp_config.multihost_interval * 2
+ *
+ *    In this case, a weak guarantee is provided.  Since the host which last had
+ *    the pool imported will suspend the pool if no mmp writes land within
+ *    fail_intervals * multihost_interval ms, the absence of writes during that
+ *    time means either the pool is not imported, or it is imported but the pool
+ *    is suspended and no further writes will occur.
+ *
+ *    Note that resuming the suspended pool on the remote host would invalidate
+ *    this guarantee, and so it is not allowed.
+ *
+ *    The factor of 2 provides a conservative safety factor and derives from
+ *    MMP_IMPORT_SAFETY_FACTOR;
+ *
+ * 2) If uberblock was written by zfs-0.8 or newer and fail_intervals == 0:
+ *    (ub_mmp_config.multihost_interval + ub_mmp_delay) *
+ *        zfs_multihost_import_intervals
+ *
+ *    In this case no guarantee can provided.  However, as long as some devices
+ *    are healthy and connected, it is likely that at least one write will land
+ *    within (multihost_interval + mmp_delay) because multihost_interval is
+ *    enough time for a write to be attempted to each leaf vdev, and mmp_delay
+ *    is enough for one to land, based on past delays.  Multiplying by
+ *    zfs_multihost_import_intervals provides a conservative safety factor.
+ *
+ * 3) If uberblock was written by zfs-0.7:
+ *    (zfs_multihost_interval + ub_mmp_delay) * zfs_multihost_import_intervals
+ *
+ *    The same logic as case #2 applies, but we do not know remote tunables.
+ *
+ *    We use the local value for zfs_multihost_interval because the original MMP
+ *    did not record this value in the uberblock.
+ *
+ *    ub_mmp_delay >= (zfs_multihost_interval / leaves), so if the other host
+ *    has a much larger zfs_multihost_interval set, ub_mmp_delay will reflect
+ *    that.  We will have waited enough time for zfs_multihost_import_intervals
+ *    writes to be issued and all but one to land.
+ *
+ *    single device pool example delays
+ *
+ *    import_delay = (1 + 1) * 20   =  40s #defaults, no I/O delay
+ *    import_delay = (1 + 10) * 20  = 220s #defaults, 10s I/O delay
+ *    import_delay = (10 + 10) * 20 = 400s #10s multihost_interval,
+ *                                          no I/O delay
+ *    100 device pool example delays
+ *
+ *    import_delay = (1 + .01) * 20 =  20s #defaults, no I/O delay
+ *    import_delay = (1 + 10) * 20  = 220s #defaults, 10s I/O delay
+ *    import_delay = (10 + .1) * 20 = 202s #10s multihost_interval,
+ *                                          no I/O delay
+ *
+ * 4) Otherwise, this uberblock was written by a pre-MMP zfs:
+ *    zfs_multihost_import_intervals * zfs_multihost_interval
+ *
+ *    In this case local tunables are used.  By default this product = 10s, long
+ *    enough for a pool with any activity at all to write at least one
+ *    uberblock.  No guarantee can be provided.
+ *
+ * Additionally, the duration is then extended by a random 25% to attempt to to
+ * detect simultaneous imports.  For example, if both partner hosts are rebooted
+ * at the same time and automatically attempt to import the pool.
  */
 
 /*
@@ -91,10 +152,9 @@
  * 'multihost' pool property is on.  This is one factor used to determine the
  * length of the activity check during import.
  *
- * The mmp write period is zfs_multihost_interval / leaf-vdevs milliseconds.
- * This means that on average an mmp write will be issued for each leaf vdev
- * every zfs_multihost_interval milliseconds.  In practice, the observed period
- * can vary with the I/O load and this observed value is the delay which is
+ * On average an mmp write will be issued for each leaf vdev every
+ * zfs_multihost_interval milliseconds.  In practice, the observed period can
+ * vary with the I/O load and this observed value is the ub_mmp_delay which is
  * stored in the uberblock.  The minimum allowed value is 100 ms.
  */
 ulong_t zfs_multihost_interval = MMP_DEFAULT_INTERVAL;
@@ -109,19 +169,21 @@ ulong_t zfs_multihost_interval = MMP_DEFAULT_INTERVAL;
 uint_t zfs_multihost_import_intervals = MMP_DEFAULT_IMPORT_INTERVALS;
 
 /*
- * Controls the behavior of the pool when mmp write failures are detected.
+ * Controls the behavior of the pool when mmp write failures or delays are
+ * detected.
  *
- * When zfs_multihost_fail_intervals = 0 then mmp write failures are ignored.
- * The failures will still be reported to the ZED which depending on its
- * configuration may take action such as suspending the pool or taking a
+ * When zfs_multihost_fail_intervals = 0, mmp write failures or delays are
+ * ignored.  The failures will still be reported to the ZED which depending on
+ * its configuration may take action such as suspending the pool or taking a
  * device offline.
  *
- * When zfs_multihost_fail_intervals > 0 then sequential mmp write failures will
- * cause the pool to be suspended.  This occurs when
- * zfs_multihost_fail_intervals * zfs_multihost_interval milliseconds have
- * passed since the last successful mmp write.  This guarantees the activity
- * test will see mmp writes if the
- * pool is imported.
+ * When zfs_multihost_fail_intervals > 0, the pool will be suspended if
+ * zfs_multihost_fail_intervals * zfs_multihost_interval milliseconds pass
+ * without a successful mmp write.  This guarantees the activity test will see
+ * mmp writes if the pool is imported.  A value of 1 is ignored and treated as
+ * if it was set to 2, because a single leaf vdev pool will issue a write once
+ * per multihost_interval and thus any variation in latency would cause the
+ * pool to be suspended.
  */
 uint_t zfs_multihost_fail_intervals = MMP_DEFAULT_FAIL_INTERVALS;
 
@@ -137,6 +199,14 @@ mmp_init(spa_t *spa)
 	cv_init(&mmp->mmp_thread_cv, NULL, CV_DEFAULT, NULL);
 	mutex_init(&mmp->mmp_io_lock, NULL, MUTEX_DEFAULT, NULL);
 	mmp->mmp_kstat_id = 1;
+
+	/*
+	 * mmp_write_done() calculates mmp_delay based on prior mmp_delay and
+	 * the elapsed time since the last write.  For the first mmp write,
+	 * there is no "last write", so we start with fake non-zero values.
+	 */
+	mmp->mmp_last_write = gethrtime();
+	mmp->mmp_delay = MSEC2NSEC(MMP_INTERVAL_OK(zfs_multihost_interval));
 }
 
 void
@@ -174,10 +244,10 @@ mmp_thread_start(spa_t *spa)
 	if (spa_writeable(spa)) {
 		mutex_enter(&mmp->mmp_thread_lock);
 		if (!mmp->mmp_thread) {
-			dprintf("mmp_thread_start pool %s\n",
-			    spa->spa_name);
 			mmp->mmp_thread = thread_create(NULL, 0, mmp_thread,
 			    spa, 0, &p0, TS_RUN, minclsyspri);
+			zfs_dbgmsg("MMP thread started pool '%s' "
+			    "gethrtime %llu", spa_name(spa), gethrtime());
 		}
 		mutex_exit(&mmp->mmp_thread_lock);
 	}
@@ -196,6 +266,8 @@ mmp_thread_stop(spa_t *spa)
 		cv_wait(&mmp->mmp_thread_cv, &mmp->mmp_thread_lock);
 	}
 	mutex_exit(&mmp->mmp_thread_lock);
+	zfs_dbgmsg("MMP thread stopped pool '%s' gethrtime %llu",
+	    spa_name(spa), gethrtime());
 
 	ASSERT(mmp->mmp_thread == NULL);
 	mmp->mmp_thread_exiting = 0;
@@ -305,7 +377,8 @@ mmp_delay_update(spa_t *spa, boolean_t write_completed
 	 * strictly less than, in case delay was changed above.
 	 */
 	if (delay < mts->mmp_delay) {
-		hrtime_t min_delay = MSEC2NSEC(zfs_multihost_interval) /
+		hrtime_t min_delay =
+		    MSEC2NSEC(MMP_INTERVAL_OK(zfs_multihost_interval)) /
 		    MAX(1, vdev_count_leaves(spa));
 		mts->mmp_delay = MAX(((delay + mts->mmp_delay * 127) / 128),
 		    min_delay);
@@ -346,6 +419,7 @@ mmp_update_uberblock(spa_t *spa, uberblock_t *ub)
 
 	mutex_enter(&mmp->mmp_io_lock);
 	mmp->mmp_ub = *ub;
+	mmp->mmp_seq = 1;
 	mmp->mmp_ub.ub_timestamp = gethrestime_sec();
 	mmp_delay_update(spa, B_TRUE);
 	mutex_exit(&mmp->mmp_io_lock);
@@ -370,8 +444,9 @@ mmp_write_uberblock(spa_t *spa)
 	spa_config_enter(spa, SCL_STATE, mmp_tag, RW_READER);
 	lock_acquire_time = gethrtime() - lock_acquire_time;
 	if (lock_acquire_time > (MSEC2NSEC(MMP_MIN_INTERVAL) / 10))
-		zfs_dbgmsg("SCL_STATE acquisition took %llu ns\n",
-		    (u_longlong_t)lock_acquire_time);
+		zfs_dbgmsg("MMP SCL_STATE acquisition pool '%s' took %llu ns "
+		    "gethrtime %llu", spa_name(spa), lock_acquire_time,
+		    gethrtime());
 
 	mutex_enter(&mmp->mmp_io_lock);
 
@@ -400,6 +475,9 @@ mmp_write_uberblock(spa_t *spa)
 			 * gethrestime_sec(), mmp->mmp_delay, NULL, 0,
 			 * mmp->mmp_kstat_id++, error);
 			 */
+			zfs_dbgmsg("MMP error choosing leaf pool '%s' "
+			    "gethrtime %llu fail_mask %#x", spa_name(spa),
+			    gethrtime(), error);
 		}
 		mutex_exit(&mmp->mmp_io_lock);
 		spa_config_exit(spa, SCL_STATE, mmp_tag);
@@ -407,16 +485,34 @@ mmp_write_uberblock(spa_t *spa)
 	}
 
 	vd = spa->spa_mmp.mmp_last_leaf;
-	mmp->mmp_skip_error = 0;
+	if (mmp->mmp_skip_error != 0) {
+		mmp->mmp_skip_error = 0;
+		zfs_dbgmsg("MMP write after skipping due to unavailable "
+		    "leaves, pool '%s' gethrtime %llu leaf %#llu",
+		    spa_name(spa), gethrtime(), vd->vdev_guid);
+	}
 
 	if (mmp->mmp_zio_root == NULL)
 		mmp->mmp_zio_root = zio_root(spa, NULL, NULL,
 		    flags | ZIO_FLAG_GODFATHER);
 
+	if (mmp->mmp_ub.ub_timestamp != gethrestime_sec()) {
+		/*
+		 * Want to reset mmp_seq when timestamp advances because after
+		 * an mmp_seq wrap new values will not be chosen by
+		 * uberblock_compare() as the "best".
+		 */
+		mmp->mmp_ub.ub_timestamp = gethrestime_sec();
+		mmp->mmp_seq = 1;
+	}
+
 	ub = &mmp->mmp_ub;
-	ub->ub_timestamp = gethrestime_sec();
 	ub->ub_mmp_magic = MMP_MAGIC;
 	ub->ub_mmp_delay = mmp->mmp_delay;
+	ub->ub_mmp_config = MMP_SEQ_SET(mmp->mmp_seq) |
+	    MMP_INTERVAL_SET(MMP_INTERVAL_OK(zfs_multihost_interval)) |
+	    MMP_FAIL_INT_SET(MMP_FAIL_INTVS_OK(
+	    zfs_multihost_fail_intervals));
 	vd->vdev_mmp_pending = gethrtime();
 	vd->vdev_mmp_kstat_id = mmp->mmp_kstat_id;
 
@@ -425,6 +521,7 @@ mmp_write_uberblock(spa_t *spa)
 	abd_zero(ub_abd, VDEV_UBERBLOCK_SIZE(vd));
 	abd_copy_from_buf(ub_abd, ub, sizeof (uberblock_t));
 
+	mmp->mmp_seq++;
 	mmp->mmp_kstat_id++;
 	mutex_exit(&mmp->mmp_io_lock);
 
@@ -450,39 +547,76 @@ mmp_thread(void *arg)
 {
 	spa_t *spa = (spa_t *)arg;
 	mmp_thread_t *mmp = &spa->spa_mmp;
-	boolean_t last_spa_suspended = spa_suspended(spa);
-	boolean_t last_spa_multihost = spa_multihost(spa);
+	boolean_t suspended = spa_suspended(spa);
+	boolean_t multihost = spa_multihost(spa);
+	uint64_t mmp_interval = MSEC2NSEC(MMP_INTERVAL_OK(
+	    zfs_multihost_interval));
+	uint32_t mmp_fail_intervals = MMP_FAIL_INTVS_OK(
+	    zfs_multihost_fail_intervals);
+	hrtime_t mmp_fail_ns = mmp_fail_intervals * mmp_interval;
+	boolean_t last_spa_suspended = suspended;
+	boolean_t last_spa_multihost = multihost;
+	uint64_t last_mmp_interval = mmp_interval;
+	uint32_t last_mmp_fail_intervals = mmp_fail_intervals;
+	hrtime_t last_mmp_fail_ns = mmp_fail_ns;
 	callb_cpr_t cpr;
-	hrtime_t max_fail_ns = zfs_multihost_fail_intervals *
-	    MSEC2NSEC(MAX(zfs_multihost_interval, MMP_MIN_INTERVAL));
+	int skip_wait = 0;
 
 	mmp_thread_enter(mmp, &cpr);
 
-	/*
-	 * The mmp_write_done() function calculates mmp_delay based on the
-	 * prior value of mmp_delay and the elapsed time since the last write.
-	 * For the first mmp write, there is no "last write", so we start
-	 * with fake, but reasonable, default non-zero values.
-	 */
-	mmp->mmp_delay = MSEC2NSEC(MAX(zfs_multihost_interval,
-	    MMP_MIN_INTERVAL)) / MAX(vdev_count_leaves(spa), 1);
-	mmp->mmp_last_write = gethrtime() - mmp->mmp_delay;
-
 	while (!mmp->mmp_thread_exiting) {
-		uint64_t mmp_fail_intervals = zfs_multihost_fail_intervals;
-		uint64_t mmp_interval = MSEC2NSEC(
-		    MAX(zfs_multihost_interval, MMP_MIN_INTERVAL));
-		boolean_t suspended = spa_suspended(spa);
-		boolean_t multihost = spa_multihost(spa);
-		hrtime_t next_time;
+		hrtime_t next_time = gethrtime() +
+		    MSEC2NSEC(MMP_DEFAULT_INTERVAL);
+		int leaves = MAX(vdev_count_leaves(spa), 1);
 
+		/* Detect changes in tunables or state */
+
+		last_spa_suspended = suspended;
+		last_spa_multihost = multihost;
+		suspended = spa_suspended(spa);
+		multihost = spa_multihost(spa);
+
+		last_mmp_interval = mmp_interval;
+		last_mmp_fail_intervals = mmp_fail_intervals;
+		last_mmp_fail_ns = mmp_fail_ns;
+		mmp_interval = MSEC2NSEC(MMP_INTERVAL_OK(
+		    zfs_multihost_interval));
+		mmp_fail_intervals = MMP_FAIL_INTVS_OK(
+		    zfs_multihost_fail_intervals);
+
+		/* Smooth so pool is not suspended when reducing tunables */
+		if (mmp_fail_intervals * mmp_interval < mmp_fail_ns) {
+			mmp_fail_ns = (mmp_fail_ns * 31 +
+			    mmp_fail_intervals * mmp_interval) / 32;
+		} else {
+			mmp_fail_ns = mmp_fail_intervals *
+			    mmp_interval;
+		}
+
+		if (mmp_interval != last_mmp_interval ||
+		    mmp_fail_intervals != last_mmp_fail_intervals) {
+			/*
+			 * We want other hosts to see new tunables as quickly as
+			 * possible.  Write out at higher frequency than usual.
+			 */
+			skip_wait += leaves;
+		}
+
 		if (multihost)
-			next_time = gethrtime() + mmp_interval /
-			    MAX(vdev_count_leaves(spa), 1);
-		else
-			next_time = gethrtime() +
-			    MSEC2NSEC(MMP_DEFAULT_INTERVAL);
+			next_time = gethrtime() + mmp_interval / leaves;
 
+		if (mmp_fail_ns != last_mmp_fail_ns) {
+			zfs_dbgmsg("MMP interval change pool '%s' "
+			    "gethrtime %llu last_mmp_interval %llu "
+			    "mmp_interval %llu last_mmp_fail_intervals %u "
+			    "mmp_fail_intervals %u mmp_fail_ns %llu "
+			    "skip_wait %d leaves %d next_time %llu",
+			    spa_name(spa), gethrtime(), last_mmp_interval,
+			    mmp_interval, last_mmp_fail_intervals,
+			    mmp_fail_intervals, mmp_fail_ns, skip_wait, leaves,
+			    next_time);
+		}
+
 		/*
 		 * MMP off => on, or suspended => !suspended:
 		 * No writes occurred recently.  Update mmp_last_write to give
@@ -490,8 +624,14 @@ mmp_thread(void *arg)
 		 */
 		if ((!last_spa_multihost && multihost) ||
 		    (last_spa_suspended && !suspended)) {
+			zfs_dbgmsg("MMP state change pool '%s': gethrtime %llu "
+			    "last_spa_multihost %u multihost %u "
+			    "last_spa_suspended %u suspended %u",
+			    spa_name(spa), last_spa_multihost, multihost,
+			    last_spa_suspended, suspended);
 			mutex_enter(&mmp->mmp_io_lock);
 			mmp->mmp_last_write = gethrtime();
+			mmp->mmp_delay = mmp_interval;
 			mutex_exit(&mmp->mmp_io_lock);
 		}
 
@@ -504,37 +644,38 @@ mmp_thread(void *arg)
 			mmp->mmp_delay = 0;
 			mutex_exit(&mmp->mmp_io_lock);
 		}
-		last_spa_multihost = multihost;
-		last_spa_suspended = suspended;
 
 		/*
-		 * Smooth max_fail_ns when its factors are decreased, because
-		 * making (max_fail_ns < mmp_interval) results in the pool being
-		 * immediately suspended before writes can occur at the new
-		 * higher frequency.
-		 */
-		if ((mmp_interval * mmp_fail_intervals) < max_fail_ns) {
-			max_fail_ns = ((31 * max_fail_ns) + (mmp_interval *
-			    mmp_fail_intervals)) / 32;
-		} else {
-			max_fail_ns = mmp_interval * mmp_fail_intervals;
-		}
-
-		/*
 		 * Suspend the pool if no MMP write has succeeded in over
 		 * mmp_interval * mmp_fail_intervals nanoseconds.
 		 */
-		if (!suspended && mmp_fail_intervals && multihost &&
-		    (gethrtime() - mmp->mmp_last_write) > max_fail_ns) {
+		if (multihost && !suspended && mmp_fail_intervals &&
+		    (gethrtime() - mmp->mmp_last_write) > mmp_fail_ns) {
+			zfs_dbgmsg("MMP suspending pool '%s': gethrtime %llu "
+			    "mmp_last_write %llu mmp_interval %llu "
+			    "mmp_fail_intervals %llu mmp_fail_ns %llu",
+			    spa_name(spa), (u_longlong_t)gethrtime(),
+			    (u_longlong_t)mmp->mmp_last_write,
+			    (u_longlong_t)mmp_interval,
+			    (u_longlong_t)mmp_fail_intervals,
+			    (u_longlong_t)mmp_fail_ns);
 			cmn_err(CE_WARN, "MMP writes to pool '%s' have not "
-			    "succeeded in over %llus; suspending pool",
+			    "succeeded in over %llu ms; suspending pool. "
+			    "Hrtime %llu",
 			    spa_name(spa),
-			    NSEC2SEC(gethrtime() - mmp->mmp_last_write));
+			    NSEC2MSEC(gethrtime() - mmp->mmp_last_write),
+			    gethrtime());
 			zio_suspend(spa, NULL, ZIO_SUSPEND_MMP);
 		}
 
 		if (multihost && !suspended)
 			mmp_write_uberblock(spa);
+
+		if (skip_wait > 0) {
+			next_time = gethrtime() + MSEC2NSEC(MMP_MIN_INTERVAL) /
+			    leaves;
+			skip_wait--;
+		}
 
 		CALLB_CPR_SAFE_BEGIN(&cpr);
 		(void) cv_timedwait_sig_hrtime(&mmp->mmp_thread_cv,

Modified: vendor-sys/illumos/dist/uts/common/fs/zfs/spa.c
==============================================================================
--- vendor-sys/illumos/dist/uts/common/fs/zfs/spa.c	Wed Nov  6 09:05:39 2019	(r354385)
+++ vendor-sys/illumos/dist/uts/common/fs/zfs/spa.c	Wed Nov  6 09:09:03 2019	(r354386)
@@ -2338,6 +2338,7 @@ spa_activity_check_required(spa_t *spa, uberblock_t *u
 	uint64_t hostid = 0;
 	uint64_t tryconfig_txg = 0;
 	uint64_t tryconfig_timestamp = 0;
+	uint16_t tryconfig_mmp_seq = 0;
 	nvlist_t *nvinfo;
 
 	if (nvlist_exists(config, ZPOOL_CONFIG_LOAD_INFO)) {
@@ -2346,6 +2347,8 @@ spa_activity_check_required(spa_t *spa, uberblock_t *u
 		    &tryconfig_txg);
 		(void) nvlist_lookup_uint64(config, ZPOOL_CONFIG_TIMESTAMP,
 		    &tryconfig_timestamp);
+		(void) nvlist_lookup_uint16(nvinfo, ZPOOL_CONFIG_MMP_SEQ,
+		    &tryconfig_mmp_seq);
 	}
 
 	(void) nvlist_lookup_uint64(config, ZPOOL_CONFIG_POOL_STATE, &state);
@@ -2362,14 +2365,17 @@ spa_activity_check_required(spa_t *spa, uberblock_t *u
 	 */
 	if (ub->ub_mmp_magic == MMP_MAGIC && ub->ub_mmp_delay == 0)
 		return (B_FALSE);
+
 	/*
-	 * If the tryconfig_* values are nonzero, they are the results of an
-	 * earlier tryimport.  If they match the uberblock we just found, then
-	 * the pool has not changed and we return false so we do not test a
-	 * second time.
+	 * If the tryconfig_ values are nonzero, they are the results of an
+	 * earlier tryimport.  If they all match the uberblock we just found,
+	 * then the pool has not changed and we return false so we do not test
+	 * a second time.
 	 */
 	if (tryconfig_txg && tryconfig_txg == ub->ub_txg &&
-	    tryconfig_timestamp && tryconfig_timestamp == ub->ub_timestamp)
+	    tryconfig_timestamp && tryconfig_timestamp == ub->ub_timestamp &&
+	    tryconfig_mmp_seq && tryconfig_mmp_seq ==
+	    (MMP_SEQ_VALID(ub) ? MMP_SEQ(ub) : 0))
 		return (B_FALSE);
 
 	/*
@@ -2393,16 +2399,87 @@ spa_activity_check_required(spa_t *spa, uberblock_t *u
 }
 
 /*
+ * Nanoseconds the activity check must watch for changes on-disk.
+ */
+static uint64_t
+spa_activity_check_duration(spa_t *spa, uberblock_t *ub)
+{
+	uint64_t import_intervals = MAX(zfs_multihost_import_intervals, 1);
+	uint64_t multihost_interval = MSEC2NSEC(
+	    MMP_INTERVAL_OK(zfs_multihost_interval));
+	uint64_t import_delay = MAX(NANOSEC, import_intervals *
+	    multihost_interval);
+
+	/*
+	 * Local tunables determine a minimum duration except for the case
+	 * where we know when the remote host will suspend the pool if MMP
+	 * writes do not land.
+	 *
+	 * See Big Theory comment at the top of mmp.c for the reasoning behind
+	 * these cases and times.
+	 */
+
+	ASSERT(MMP_IMPORT_SAFETY_FACTOR >= 100);
+
+	if (MMP_INTERVAL_VALID(ub) && MMP_FAIL_INT_VALID(ub) &&
+	    MMP_FAIL_INT(ub) > 0) {
+
+		/* MMP on remote host will suspend pool after failed writes */
+		import_delay = MMP_FAIL_INT(ub) * MSEC2NSEC(MMP_INTERVAL(ub)) *
+		    MMP_IMPORT_SAFETY_FACTOR / 100;
+
+		zfs_dbgmsg("fail_intvals>0 import_delay=%llu ub_mmp "
+		    "mmp_fails=%llu ub_mmp mmp_interval=%llu "
+		    "import_intervals=%u", import_delay, MMP_FAIL_INT(ub),
+		    MMP_INTERVAL(ub), import_intervals);
+
+	} else if (MMP_INTERVAL_VALID(ub) && MMP_FAIL_INT_VALID(ub) &&
+	    MMP_FAIL_INT(ub) == 0) {
+
+		/* MMP on remote host will never suspend pool */
+		import_delay = MAX(import_delay, (MSEC2NSEC(MMP_INTERVAL(ub)) +
+		    ub->ub_mmp_delay) * import_intervals);
+
+		zfs_dbgmsg("fail_intvals=0 import_delay=%llu ub_mmp "
+		    "mmp_interval=%llu ub_mmp_delay=%llu "
+		    "import_intervals=%u", import_delay, MMP_INTERVAL(ub),
+		    ub->ub_mmp_delay, import_intervals);
+
+	} else if (MMP_VALID(ub)) {
+		/*
+		 * zfs-0.7 compatability case
+		 */
+
+		import_delay = MAX(import_delay, (multihost_interval +
+		    ub->ub_mmp_delay) * import_intervals);
+
+		zfs_dbgmsg("import_delay=%llu ub_mmp_delay=%llu "
+		    "import_intervals=%u leaves=%u", import_delay,
+		    ub->ub_mmp_delay, import_intervals,
+		    vdev_count_leaves(spa));
+	} else {
+		/* Using local tunings is the only reasonable option */
+		zfs_dbgmsg("pool last imported on non-MMP aware "
+		    "host using import_delay=%llu multihost_interval=%llu "
+		    "import_intervals=%u", import_delay, multihost_interval,
+		    import_intervals);
+	}
+
+	return (import_delay);
+}
+
+/*
  * Perform the import activity check.  If the user canceled the import or
  * we detected activity then fail.
  */
 static int
 spa_activity_check(spa_t *spa, uberblock_t *ub, nvlist_t *config)
 {
-	uint64_t import_intervals = MAX(zfs_multihost_import_intervals, 1);
 	uint64_t txg = ub->ub_txg;
 	uint64_t timestamp = ub->ub_timestamp;
-	uint64_t import_delay = NANOSEC;
+	uint64_t mmp_config = ub->ub_mmp_config;
+	uint16_t mmp_seq = MMP_SEQ_VALID(ub) ? MMP_SEQ(ub) : 0;
+	uint64_t import_delay;
 	hrtime_t import_expire;
 	nvlist_t *mmp_label = NULL;
 	vdev_t *rvd = spa->spa_root_vdev;
@@ -2419,7 +2496,7 @@ spa_activity_check(spa_t *spa, uberblock_t *ub, nvlist
 	 * during the earlier tryimport.  If the txg recorded there is 0 then
 	 * the pool is known to be active on another host.
 	 *
-	 * Otherwise, the pool might be in use on another node.  Check for
+	 * Otherwise, the pool might be in use on another host.  Check for
 	 * changes in the uberblocks on disk if necessary.
 	 */
 	if (nvlist_exists(config, ZPOOL_CONFIG_LOAD_INFO)) {
@@ -2434,32 +2511,25 @@ spa_activity_check(spa_t *spa, uberblock_t *ub, nvlist
 		}
 	}
 
-	/*
-	 * Preferentially use the zfs_multihost_interval from the node which
-	 * last imported the pool.  This value is stored in an MMP uberblock as.
-	 *
-	 * ub_mmp_delay * vdev_count_leaves() == zfs_multihost_interval
-	 */
-	if (ub->ub_mmp_magic == MMP_MAGIC && ub->ub_mmp_delay)
-		import_delay = MAX(import_delay, import_intervals *
-		    ub->ub_mmp_delay * MAX(vdev_count_leaves(spa), 1));
+	import_delay = spa_activity_check_duration(spa, ub);
 
-	/* Apply a floor using the local default values. */
-	import_delay = MAX(import_delay, import_intervals *
-	    MSEC2NSEC(MAX(zfs_multihost_interval, MMP_MIN_INTERVAL)));
-
-	zfs_dbgmsg("import_delay=%llu ub_mmp_delay=%llu import_intervals=%u "
-	    "leaves=%u", import_delay, ub->ub_mmp_delay, import_intervals,
-	    vdev_count_leaves(spa));
-
 	/* Add a small random factor in case of simultaneous imports (0-25%) */
-	import_expire = gethrtime() + import_delay +
-	    (import_delay * spa_get_random(250) / 1000);
+	import_delay += import_delay * spa_get_random(250) / 1000;
 
+	import_expire = gethrtime() + import_delay;
+
 	while (gethrtime() < import_expire) {
 		vdev_uberblock_load(rvd, ub, &mmp_label);
 
-		if (txg != ub->ub_txg || timestamp != ub->ub_timestamp) {
+		if (txg != ub->ub_txg || timestamp != ub->ub_timestamp ||
+		    mmp_seq != (MMP_SEQ_VALID(ub) ? MMP_SEQ(ub) : 0)) {
+			zfs_dbgmsg("multihost activity detected "
+			    "txg %llu ub_txg  %llu "
+			    "timestamp %llu ub_timestamp  %llu "
+			    "mmp_config %#llx ub_mmp_config %#llx",
+			    txg, ub->ub_txg, timestamp, ub->ub_timestamp,
+			    mmp_config, ub->ub_mmp_config);
+
 			error = SET_ERROR(EREMOTEIO);
 			break;
 		}
@@ -2844,6 +2914,9 @@ spa_ld_select_uberblock(spa_t *spa, spa_import_type_t 
 		    ZPOOL_CONFIG_MMP_STATE, MMP_STATE_INACTIVE);
 		fnvlist_add_uint64(spa->spa_load_info,
 		    ZPOOL_CONFIG_MMP_TXG, ub->ub_txg);
+		fnvlist_add_uint16(spa->spa_load_info,
+		    ZPOOL_CONFIG_MMP_SEQ,
+		    (MMP_SEQ_VALID(ub) ? MMP_SEQ(ub) : 0));
 	}
 
 	/*

Modified: vendor-sys/illumos/dist/uts/common/fs/zfs/sys/mmp.h
==============================================================================
--- vendor-sys/illumos/dist/uts/common/fs/zfs/sys/mmp.h	Wed Nov  6 09:05:39 2019	(r354385)
+++ vendor-sys/illumos/dist/uts/common/fs/zfs/sys/mmp.h	Wed Nov  6 09:09:03 2019	(r354386)
@@ -29,8 +29,13 @@ extern "C" {
 
 #define	MMP_MIN_INTERVAL		100	/* ms */
 #define	MMP_DEFAULT_INTERVAL		1000	/* ms */
-#define	MMP_DEFAULT_IMPORT_INTERVALS	10
-#define	MMP_DEFAULT_FAIL_INTERVALS	5
+#define	MMP_DEFAULT_IMPORT_INTERVALS	20
+#define	MMP_DEFAULT_FAIL_INTERVALS	10
+#define	MMP_MIN_FAIL_INTERVALS		2	/* min if != 0 */
+#define	MMP_IMPORT_SAFETY_FACTOR	200	/* pct */
+#define	MMP_INTERVAL_OK(interval)	MAX(interval, MMP_MIN_INTERVAL)
+#define	MMP_FAIL_INTVS_OK(fails)	(fails == 0 ? 0 : MAX(fails, \
+					    MMP_MIN_FAIL_INTERVALS))
 
 typedef struct mmp_thread {
 	kmutex_t	mmp_thread_lock; /* protect thread mgmt fields */
@@ -46,6 +51,7 @@ typedef struct mmp_thread {
 	int		mmp_skip_error; /* reason for last skipped write */
 	vdev_t		*mmp_last_leaf;	/* last mmp write sent here */
 	uint64_t	mmp_leaf_last_gen;	/* last mmp write sent here */
+	uint32_t	mmp_seq;	/* intra-second update counter */
 } mmp_thread_t;
 
 

Modified: vendor-sys/illumos/dist/uts/common/fs/zfs/sys/uberblock_impl.h
==============================================================================
--- vendor-sys/illumos/dist/uts/common/fs/zfs/sys/uberblock_impl.h	Wed Nov  6 09:05:39 2019	(r354385)
+++ vendor-sys/illumos/dist/uts/common/fs/zfs/sys/uberblock_impl.h	Wed Nov  6 09:09:03 2019	(r354386)
@@ -44,8 +44,37 @@ extern "C" {
  */
 #define	UBERBLOCK_MAGIC		0x00bab10c		/* oo-ba-bloc!	*/
 #define	UBERBLOCK_SHIFT		10			/* up to 1K	*/
-#define	MMP_MAGIC		0xa11cea11		/* all-see-all  */
+#define	MMP_MAGIC		0xa11cea11		/* all-see-all	*/
 
+#define	MMP_INTERVAL_VALID_BIT	0x01
+#define	MMP_SEQ_VALID_BIT	0x02
+#define	MMP_FAIL_INT_VALID_BIT	0x04
+
+#define	MMP_VALID(ubp)		(ubp->ub_magic == UBERBLOCK_MAGIC && \
+				    ubp->ub_mmp_magic == MMP_MAGIC)
+#define	MMP_INTERVAL_VALID(ubp)	(MMP_VALID(ubp) && (ubp->ub_mmp_config & \
+				    MMP_INTERVAL_VALID_BIT))
+#define	MMP_SEQ_VALID(ubp)	(MMP_VALID(ubp) && (ubp->ub_mmp_config & \
+				    MMP_SEQ_VALID_BIT))
+#define	MMP_FAIL_INT_VALID(ubp)	(MMP_VALID(ubp) && (ubp->ub_mmp_config & \
+				    MMP_FAIL_INT_VALID_BIT))
+
+#define	MMP_INTERVAL(ubp)	((ubp->ub_mmp_config & 0x00000000FFFFFF00) \
+				    >> 8)
+#define	MMP_SEQ(ubp)		((ubp->ub_mmp_config & 0x0000FFFF00000000) \
+				    >> 32)
+#define	MMP_FAIL_INT(ubp)	((ubp->ub_mmp_config & 0xFFFF000000000000) \
+				    >> 48)
+
+#define	MMP_INTERVAL_SET(write) \
+	    (((uint64_t)(write & 0xFFFFFF) << 8) | MMP_INTERVAL_VALID_BIT)
+
+#define	MMP_SEQ_SET(seq) \
+	    (((uint64_t)(seq & 0xFFFF) << 32) | MMP_SEQ_VALID_BIT)
+
+#define	MMP_FAIL_INT_SET(fail) \
+	    (((uint64_t)(fail & 0xFFFF) << 48) | MMP_FAIL_INT_VALID_BIT)
+
 struct uberblock {
 	uint64_t	ub_magic;	/* UBERBLOCK_MAGIC		*/
 	uint64_t	ub_version;	/* SPA_VERSION			*/
@@ -59,8 +88,31 @@ struct uberblock {
 
 	/* Maybe missing in uberblocks we read, but always written */
 	uint64_t	ub_mmp_magic;
+	/*
+	 * If ub_mmp_delay == 0 and ub_mmp_magic is valid, MMP is off.
+	 * Otherwise, nanosec since last MMP write.
+	 */
 	uint64_t	ub_mmp_delay;
-	uint64_t	ub_mmp_seq;
+
+	/*
+	 * The ub_mmp_config contains the multihost write interval, multihost
+	 * fail intervals, sequence number for sub-second granularity, and
+	 * valid bit mask.  This layout is as follows:
+	 *
+	 *   64      56      48      40      32      24      16      8       0
+	 *   +-------+-------+-------+-------+-------+-------+-------+-------+
+	 * 0 | Fail Intervals|      Seq      |   Write Interval (ms) | VALID |
+	 *   +-------+-------+-------+-------+-------+-------+-------+-------+
+	 *
+	 * This allows a write_interval of (2^24/1000)s, over 4.5 hours
+	 *
+	 * VALID Bits:
+	 * - 0x01 - Write Interval (ms)
+	 * - 0x02 - Sequence number exists
+	 * - 0x04 - Fail Intervals
+	 * - 0xf8 - Reserved
+	 */
+	uint64_t	ub_mmp_config;
 
 	/*
 	 * ub_checkpoint_txg indicates two things about the current uberblock:

Modified: vendor-sys/illumos/dist/uts/common/fs/zfs/uberblock.c
==============================================================================
--- vendor-sys/illumos/dist/uts/common/fs/zfs/uberblock.c	Wed Nov  6 09:05:39 2019	(r354385)
+++ vendor-sys/illumos/dist/uts/common/fs/zfs/uberblock.c	Wed Nov  6 09:09:03 2019	(r354386)
@@ -26,6 +26,7 @@
 #include <sys/zfs_context.h>
 #include <sys/uberblock_impl.h>
 #include <sys/vdev_impl.h>
+#include <sys/mmp.h>
 
 int
 uberblock_verify(uberblock_t *ub)
@@ -58,8 +59,15 @@ uberblock_update(uberblock_t *ub, vdev_t *rvd, uint64_
 	ub->ub_timestamp = gethrestime_sec();
 	ub->ub_software_version = SPA_VERSION;
 	ub->ub_mmp_magic = MMP_MAGIC;
-	ub->ub_mmp_delay = spa_multihost(rvd->vdev_spa) ? mmp_delay : 0;
-	ub->ub_mmp_seq = 0;
+	if (spa_multihost(rvd->vdev_spa)) {
+		ub->ub_mmp_delay = mmp_delay;
+		ub->ub_mmp_config = MMP_SEQ_SET(0) |
+		    MMP_INTERVAL_SET(zfs_multihost_interval) |
+		    MMP_FAIL_INT_SET(zfs_multihost_fail_intervals);
+	} else {
+		ub->ub_mmp_delay = 0;
+		ub->ub_mmp_config = 0;
+	}
 	ub->ub_checkpoint_txg = 0;
 
 	return (ub->ub_rootbp.blk_birth == txg);

Modified: vendor-sys/illumos/dist/uts/common/fs/zfs/vdev_label.c
==============================================================================
--- vendor-sys/illumos/dist/uts/common/fs/zfs/vdev_label.c	Wed Nov  6 09:05:39 2019	(r354385)
+++ vendor-sys/illumos/dist/uts/common/fs/zfs/vdev_label.c	Wed Nov  6 09:09:03 2019	(r354386)
@@ -1016,10 +1016,35 @@ static int
 vdev_uberblock_compare(const uberblock_t *ub1, const uberblock_t *ub2)
 {
 	int cmp = AVL_CMP(ub1->ub_txg, ub2->ub_txg);
+
 	if (likely(cmp))
 		return (cmp);
 
-	return (AVL_CMP(ub1->ub_timestamp, ub2->ub_timestamp));
+	cmp = AVL_CMP(ub1->ub_timestamp, ub2->ub_timestamp);
+	if (likely(cmp))
+		return (cmp);
+
+	/*
+	 * If MMP_VALID(ub) && MMP_SEQ_VALID(ub) then the host has an MMP-aware
+	 * ZFS, e.g. zfsonlinux >= 0.7.
+	 *
+	 * If one ub has MMP and the other does not, they were written by
+	 * different hosts, which matters for MMP.  So we treat no MMP/no SEQ as
+	 * a 0 value.
+	 *
+	 * Since timestamp and txg are the same if we get this far, either is
+	 * acceptable for importing the pool.
+	 */
+	unsigned int seq1 = 0;
+	unsigned int seq2 = 0;
+
+	if (MMP_VALID(ub1) && MMP_SEQ_VALID(ub1))
+		seq1 = MMP_SEQ(ub1);
+
+	if (MMP_VALID(ub2) && MMP_SEQ_VALID(ub2))
+		seq2 = MMP_SEQ(ub2);
+
+	return (AVL_CMP(seq1, seq2));
 }
 
 struct ubl_cbdata {

Modified: vendor-sys/illumos/dist/uts/common/sys/fs/zfs.h
==============================================================================
--- vendor-sys/illumos/dist/uts/common/sys/fs/zfs.h	Wed Nov  6 09:05:39 2019	(r354385)
+++ vendor-sys/illumos/dist/uts/common/sys/fs/zfs.h	Wed Nov  6 09:09:03 2019	(r354386)
@@ -600,6 +600,7 @@ typedef struct zpool_load_policy {
 #define	ZPOOL_CONFIG_CACHEFILE		"cachefile"	/* not stored on disk */
 #define	ZPOOL_CONFIG_MMP_STATE		"mmp_state"	/* not stored on disk */
 #define	ZPOOL_CONFIG_MMP_TXG		"mmp_txg"	/* not stored on disk */
+#define	ZPOOL_CONFIG_MMP_SEQ		"mmp_seq"	/* not stored on disk */
 #define	ZPOOL_CONFIG_MMP_HOSTNAME	"mmp_hostname"	/* not stored on disk */
 #define	ZPOOL_CONFIG_MMP_HOSTID		"mmp_hostid"	/* not stored on disk */
 #define	ZPOOL_CONFIG_ALLOCATION_BIAS	"alloc_bias"	/* not stored on disk */


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