Log Spacemap Project

= Motivation At Delphix we've seen a lot of customer systems where fragmentation is over 75% and random writes take a performance hit because a lot of time is spend on I/Os that update on-disk space accounting metadata. Specifically, we seen cases where 20% to 40% of sync time is spend after sync pass 1 and ~30% of the I/Os on the system is spent updating spacemaps. The problem is that these pools have existed long enough that we've touched almost every metaslab at least once, and random writes scatter frees across all metaslabs every TXG, thus appending to their spacemaps and resulting in many I/Os. To give an example, assuming that every VDEV has 200 metaslabs and our writes fit within a single spacemap block (generally 4K) we have 200 I/Os. Then if we assume 2 levels of indirection, we need 400 additional I/Os and since we are talking about metadata for which we keep 2 extra copies for redundancy we need to triple that number, leading to a total of 1800 I/Os per VDEV every TXG. We could try and decrease the number of metaslabs so we have less I/Os per TXG but then each metaslab would cover a wider range on disk and thus would take more time to be loaded in memory from disk. In addition, after it's loaded, it's range tree would consume more memory. Another idea would be to just increase the spacemap block size which would allow us to fit more entries within an I/O block resulting in fewer I/Os per metaslab and a speedup in loading time. The problem is still that we don't deal with the number of I/Os going up as the number of metaslabs is increasing and the fact is that we generally write a lot to a few metaslabs and a little to the rest of them. Thus, just increasing the block size would actually waste bandwidth because we won't be utilizing our bigger block size. = About this patch This patch introduces the Log Spacemap project which provides the solution to the above problem while taking into account all the aforementioned tradeoffs. The details on how it achieves that can be found in the references sections below and in the code (see Big Theory Statement in spa_log_spacemap.c). Even though the change is fairly constraint within the metaslab and lower-level SPA codepaths, there is a side-change that is user-facing. The change is that VDEV IDs from VDEV holes will no longer be reused. To give some background and reasoning for this, when a log device is removed and its VDEV structure was replaced with a hole (or was compacted; if at the end of the vdev array), its vdev_id could be reused by devices added after that. Now with the pool-wide space maps recording the vdev ID, this behavior can cause problems (e.g. is this entry referring to a segment in the new vdev or the removed log?). Thus, to simplify things the ID reuse behavior is gone and now vdev IDs for top-level vdevs are truly unique within a pool. = Testing The illumos implementation of this feature has been used internally for a year and has been in production for ~6 months. For this patch specifically there don't seem to be any regressions introduced to ZTS and I have been running zloop for a week without any related problems. = Performance Analysis (Linux Specific) All performance results and analysis for illumos can be found in the links of the references. Redoing the same experiments in Linux gave similar results. Below are the specifics of the Linux run. After the pool reached stable state the percentage of the time spent in pass 1 per TXG was 64% on average for the stock bits while the log spacemap bits stayed at 95% during the experiment (graph: sdimitro.github.io/img/linux-lsm/PercOfSyncInPassOne.png). Sync times per TXG were 37.6 seconds on average for the stock bits and 22.7 seconds for the log spacemap bits (related graph: sdimitro.github.io/img/linux-lsm/SyncTimePerTXG.png). As a result the log spacemap bits were able to push more TXGs, which is also the reason why all graphs quantified per TXG have more entries for the log spacemap bits. Another interesting aspect in terms of txg syncs is that the stock bits had 22% of their TXGs reach sync pass 7, 55% reach sync pass 8, and 20% reach 9. The log space map bits reached sync pass 4 in 79% of their TXGs, sync pass 7 in 19%, and sync pass 8 at 1%. This emphasizes the fact that not only we spend less time on metadata but we also iterate less times to convergence in spa_sync() dirtying objects. [related graphs: stock- sdimitro.github.io/img/linux-lsm/NumberOfPassesPerTXGStock.png lsm- sdimitro.github.io/img/linux-lsm/NumberOfPassesPerTXGLSM.png] Finally, the improvement in IOPs that the userland gains from the change is approximately 40%. There is a consistent win in IOPS as you can see from the graphs below but the absolute amount of improvement that the log spacemap gives varies within each minute interval. sdimitro.github.io/img/linux-lsm/StockVsLog3Days.png sdimitro.github.io/img/linux-lsm/StockVsLog10Hours.png = Porting to Other Platforms For people that want to port this commit to other platforms below is a list of ZoL commits that this patch depends on: Make zdb results for checkpoint tests consistent db587941c5 Update vdev_is_spacemap_addressable() for new spacemap encoding 419ba59145 Simplify spa_sync by breaking it up to smaller functions 8dc2197b7b Factor metaslab_load_wait() in metaslab_load() b194fab0fb Rename range_tree_verify to range_tree_verify_not_present df72b8bebe Change target size of metaslabs from 256GB to 16GB c853f382db zdb -L should skip leak detection altogether 21e7cf5da8 vs_alloc can underflow in L2ARC vdevs 7558997d2f Simplify log vdev removal code 6c926f426a Get rid of space_map_update() for ms_synced_length 425d3237ee Introduce auxiliary metaslab histograms 928e8ad47d Error path in metaslab_load_impl() forgets to drop ms_sync_lock 8eef997679 = References Background, Motivation, and Internals of the Feature - OpenZFS 2017 Presentation: youtu.be/jj2IxRkl5bQ - Slides: slideshare.net/SerapheimNikolaosDim/zfs-log-spacemaps-project Flushing Algorithm Internals & Performance Results (Illumos Specific) - Blogpost: sdimitro.github.io/post/zfs-lsm-flushing/ - OpenZFS 2018 Presentation: youtu.be/x6D2dHRjkxw - Slides: slideshare.net/SerapheimNikolaosDim/zfs-log-spacemap-flushing-algorithm Upstream Delphix Issues: DLPX-51539, DLPX-59659, DLPX-57783, DLPX-61438, DLPX-41227, DLPX-59320 DLPX-63385 Reviewed-by: Sean Eric Fagan <sef@ixsystems.com> Reviewed-by: Matt Ahrens <matt@delphix.com> Reviewed-by: George Wilson <gwilson@delphix.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Serapheim Dimitropoulos <serapheim@delphix.com> Closes #8442
2026-05-23 10:54:35 +03:00 · 2019-07-16 10:11:49 -07:00
parent df834a7ccc
commit 93e28d661e
41 changed files with 3196 additions and 333 deletions
@@ -812,6 +812,12 @@ get_checkpoint_refcount(vdev_t *vd)
 	return (refcount);
 }

+static int
+get_log_spacemap_refcount(spa_t *spa)
+{
+	return (avl_numnodes(&spa->spa_sm_logs_by_txg));
+}
+
 static int
 verify_spacemap_refcounts(spa_t *spa)
 {
@@ -826,6 +832,7 @@ verify_spacemap_refcounts(spa_t *spa)
 	actual_refcount += get_obsolete_refcount(spa->spa_root_vdev);
 	actual_refcount += get_prev_obsolete_spacemap_refcount(spa);
 	actual_refcount += get_checkpoint_refcount(spa->spa_root_vdev);
+	actual_refcount += get_log_spacemap_refcount(spa);

 	if (expected_refcount != actual_refcount) {
 		(void) printf("space map refcount mismatch: expected %lld != "
@@ -924,7 +931,7 @@ dump_spacemap(objset_t *os, space_map_t *sm)
 			alloc -= entry_run;
 		entry_id++;
 	}
-	if ((uint64_t)alloc != space_map_allocated(sm)) {
+	if (alloc != space_map_allocated(sm)) {
 		(void) printf("space_map_object alloc (%lld) INCONSISTENT "
 		    "with space map summary (%lld)\n",
 		    (longlong_t)space_map_allocated(sm), (longlong_t)alloc);
@@ -990,23 +997,45 @@ dump_metaslab(metaslab_t *msp)

 	ASSERT(msp->ms_size == (1ULL << vd->vdev_ms_shift));
 	dump_spacemap(spa->spa_meta_objset, msp->ms_sm);
+
+	if (spa_feature_is_active(spa, SPA_FEATURE_LOG_SPACEMAP)) {
+		(void) printf("\tFlush data:\n\tunflushed txg=%llu\n\n",
+		    (u_longlong_t)metaslab_unflushed_txg(msp));
+	}
 }

 static void
 print_vdev_metaslab_header(vdev_t *vd)
 {
 	vdev_alloc_bias_t alloc_bias = vd->vdev_alloc_bias;
-	const char *bias_str;
+	const char *bias_str = "";
+	if (alloc_bias == VDEV_BIAS_LOG || vd->vdev_islog) {
+		bias_str = VDEV_ALLOC_BIAS_LOG;
+	} else if (alloc_bias == VDEV_BIAS_SPECIAL) {
+		bias_str = VDEV_ALLOC_BIAS_SPECIAL;
+	} else if (alloc_bias == VDEV_BIAS_DEDUP) {
+		bias_str = VDEV_ALLOC_BIAS_DEDUP;
+	}

-	bias_str = (alloc_bias == VDEV_BIAS_LOG || vd->vdev_islog) ?
-	    VDEV_ALLOC_BIAS_LOG :
-	    (alloc_bias == VDEV_BIAS_SPECIAL) ? VDEV_ALLOC_BIAS_SPECIAL :
-	    (alloc_bias == VDEV_BIAS_DEDUP) ? VDEV_ALLOC_BIAS_DEDUP :
-	    vd->vdev_islog ? "log" : "";
+	uint64_t ms_flush_data_obj = 0;
+	if (vd->vdev_top_zap != 0) {
+		int error = zap_lookup(spa_meta_objset(vd->vdev_spa),
+		    vd->vdev_top_zap, VDEV_TOP_ZAP_MS_UNFLUSHED_PHYS_TXGS,
+		    sizeof (uint64_t), 1, &ms_flush_data_obj);
+		if (error != ENOENT) {
+			ASSERT0(error);
+		}
+	}

-	(void) printf("\tvdev %10llu   %s\n"
-	    "\t%-10s%5llu   %-19s   %-15s   %-12s\n",
-	    (u_longlong_t)vd->vdev_id, bias_str,
+	(void) printf("\tvdev %10llu   %s",
+	    (u_longlong_t)vd->vdev_id, bias_str);
+
+	if (ms_flush_data_obj != 0) {
+		(void) printf("   ms_unflushed_phys object %llu",
+		    (u_longlong_t)ms_flush_data_obj);
+	}
+
+	(void) printf("\n\t%-10s%5llu   %-19s   %-15s   %-12s\n",
 	    "metaslabs", (u_longlong_t)vd->vdev_ms_count,
 	    "offset", "spacemap", "free");
 	(void) printf("\t%15s   %19s   %15s   %12s\n",
@@ -1172,6 +1201,24 @@ dump_metaslabs(spa_t *spa)
 	}
 }

+static void
+dump_log_spacemaps(spa_t *spa)
+{
+	(void) printf("\nLog Space Maps in Pool:\n");
+	for (spa_log_sm_t *sls = avl_first(&spa->spa_sm_logs_by_txg);
+	    sls; sls = AVL_NEXT(&spa->spa_sm_logs_by_txg, sls)) {
+		space_map_t *sm = NULL;
+		VERIFY0(space_map_open(&sm, spa_meta_objset(spa),
+		    sls->sls_sm_obj, 0, UINT64_MAX, SPA_MINBLOCKSHIFT));
+
+		(void) printf("Log Spacemap object %llu txg %llu\n",
+		    (u_longlong_t)sls->sls_sm_obj, (u_longlong_t)sls->sls_txg);
+		dump_spacemap(spa->spa_meta_objset, sm);
+		space_map_close(sm);
+	}
+	(void) printf("\n");
+}
+
 static void
 dump_dde(const ddt_t *ddt, const ddt_entry_t *dde, uint64_t index)
 {
@@ -3782,6 +3829,84 @@ static metaslab_ops_t zdb_metaslab_ops = {
 	NULL	/* alloc */
 };

+typedef int (*zdb_log_sm_cb_t)(spa_t *spa, space_map_entry_t *sme,
+    uint64_t txg, void *arg);
+
+typedef struct unflushed_iter_cb_arg {
+	spa_t *uic_spa;
+	uint64_t uic_txg;
+	void *uic_arg;
+	zdb_log_sm_cb_t uic_cb;
+} unflushed_iter_cb_arg_t;
+
+static int
+iterate_through_spacemap_logs_cb(space_map_entry_t *sme, void *arg)
+{
+	unflushed_iter_cb_arg_t *uic = arg;
+	return (uic->uic_cb(uic->uic_spa, sme, uic->uic_txg, uic->uic_arg));
+}
+
+static void
+iterate_through_spacemap_logs(spa_t *spa, zdb_log_sm_cb_t cb, void *arg)
+{
+	if (!spa_feature_is_active(spa, SPA_FEATURE_LOG_SPACEMAP))
+		return;
+
+	spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
+	for (spa_log_sm_t *sls = avl_first(&spa->spa_sm_logs_by_txg);
+	    sls; sls = AVL_NEXT(&spa->spa_sm_logs_by_txg, sls)) {
+		space_map_t *sm = NULL;
+		VERIFY0(space_map_open(&sm, spa_meta_objset(spa),
+		    sls->sls_sm_obj, 0, UINT64_MAX, SPA_MINBLOCKSHIFT));
+
+		unflushed_iter_cb_arg_t uic = {
+			.uic_spa = spa,
+			.uic_txg = sls->sls_txg,
+			.uic_arg = arg,
+			.uic_cb = cb
+		};
+
+		VERIFY0(space_map_iterate(sm, space_map_length(sm),
+		    iterate_through_spacemap_logs_cb, &uic));
+		space_map_close(sm);
+	}
+	spa_config_exit(spa, SCL_CONFIG, FTAG);
+}
+
+/* ARGSUSED */
+static int
+load_unflushed_svr_segs_cb(spa_t *spa, space_map_entry_t *sme,
+    uint64_t txg, void *arg)
+{
+	spa_vdev_removal_t *svr = arg;
+
+	uint64_t offset = sme->sme_offset;
+	uint64_t size = sme->sme_run;
+
+	/* skip vdevs we don't care about */
+	if (sme->sme_vdev != svr->svr_vdev_id)
+		return (0);
+
+	vdev_t *vd = vdev_lookup_top(spa, sme->sme_vdev);
+	metaslab_t *ms = vd->vdev_ms[offset >> vd->vdev_ms_shift];
+	ASSERT(sme->sme_type == SM_ALLOC || sme->sme_type == SM_FREE);
+
+	if (txg < metaslab_unflushed_txg(ms))
+		return (0);
+
+	vdev_indirect_mapping_t *vim = vd->vdev_indirect_mapping;
+	ASSERT(vim != NULL);
+	if (offset >= vdev_indirect_mapping_max_offset(vim))
+		return (0);
+
+	if (sme->sme_type == SM_ALLOC)
+		range_tree_add(svr->svr_allocd_segs, offset, size);
+	else
+		range_tree_remove(svr->svr_allocd_segs, offset, size);
+
+	return (0);
+}
+
 /* ARGSUSED */
 static void
 claim_segment_impl_cb(uint64_t inner_offset, vdev_t *vd, uint64_t offset,
@@ -3830,36 +3955,35 @@ zdb_claim_removing(spa_t *spa, zdb_cb_t *zcb)
 	vdev_t *vd = vdev_lookup_top(spa, svr->svr_vdev_id);
 	vdev_indirect_mapping_t *vim = vd->vdev_indirect_mapping;

+	ASSERT0(range_tree_space(svr->svr_allocd_segs));
+
+	range_tree_t *allocs = range_tree_create(NULL, NULL);
 	for (uint64_t msi = 0; msi < vd->vdev_ms_count; msi++) {
 		metaslab_t *msp = vd->vdev_ms[msi];

 		if (msp->ms_start >= vdev_indirect_mapping_max_offset(vim))
 			break;

-		ASSERT0(range_tree_space(svr->svr_allocd_segs));
-
-		if (msp->ms_sm != NULL) {
-			VERIFY0(space_map_load(msp->ms_sm,
-			    svr->svr_allocd_segs, SM_ALLOC));
-
-			/*
-			 * Clear everything past what has been synced unless
-			 * it's past the spacemap, because we have not allocated
-			 * mappings for it yet.
-			 */
-			uint64_t vim_max_offset =
-			    vdev_indirect_mapping_max_offset(vim);
-			uint64_t sm_end = msp->ms_sm->sm_start +
-			    msp->ms_sm->sm_size;
-			if (sm_end > vim_max_offset)
-				range_tree_clear(svr->svr_allocd_segs,
-				    vim_max_offset, sm_end - vim_max_offset);
-		}
-
-		zcb->zcb_removing_size +=
-		    range_tree_space(svr->svr_allocd_segs);
-		range_tree_vacate(svr->svr_allocd_segs, claim_segment_cb, vd);
+		ASSERT0(range_tree_space(allocs));
+		if (msp->ms_sm != NULL)
+			VERIFY0(space_map_load(msp->ms_sm, allocs, SM_ALLOC));
+		range_tree_vacate(allocs, range_tree_add, svr->svr_allocd_segs);
 	}
+	range_tree_destroy(allocs);
+
+	iterate_through_spacemap_logs(spa, load_unflushed_svr_segs_cb, svr);
+
+	/*
+	 * Clear everything past what has been synced,
+	 * because we have not allocated mappings for
+	 * it yet.
+	 */
+	range_tree_clear(svr->svr_allocd_segs,
+	    vdev_indirect_mapping_max_offset(vim),
+	    vd->vdev_asize - vdev_indirect_mapping_max_offset(vim));
+
+	zcb->zcb_removing_size += range_tree_space(svr->svr_allocd_segs);
+	range_tree_vacate(svr->svr_allocd_segs, claim_segment_cb, vd);

 	spa_config_exit(spa, SCL_CONFIG, FTAG);
 }
@@ -4070,6 +4194,82 @@ zdb_leak_init_exclude_checkpoint(spa_t *spa, zdb_cb_t *zcb)
 	}
 }

+static int
+count_unflushed_space_cb(spa_t *spa, space_map_entry_t *sme,
+    uint64_t txg, void *arg)
+{
+	int64_t *ualloc_space = arg;
+
+	uint64_t offset = sme->sme_offset;
+	uint64_t vdev_id = sme->sme_vdev;
+
+	vdev_t *vd = vdev_lookup_top(spa, vdev_id);
+	if (!vdev_is_concrete(vd))
+		return (0);
+
+	metaslab_t *ms = vd->vdev_ms[offset >> vd->vdev_ms_shift];
+	ASSERT(sme->sme_type == SM_ALLOC || sme->sme_type == SM_FREE);
+
+	if (txg < metaslab_unflushed_txg(ms))
+		return (0);
+
+	if (sme->sme_type == SM_ALLOC)
+		*ualloc_space += sme->sme_run;
+	else
+		*ualloc_space -= sme->sme_run;
+
+	return (0);
+}
+
+static int64_t
+get_unflushed_alloc_space(spa_t *spa)
+{
+	if (dump_opt['L'])
+		return (0);
+
+	int64_t ualloc_space = 0;
+	iterate_through_spacemap_logs(spa, count_unflushed_space_cb,
+	    &ualloc_space);
+	return (ualloc_space);
+}
+
+static int
+load_unflushed_cb(spa_t *spa, space_map_entry_t *sme, uint64_t txg, void *arg)
+{
+	maptype_t *uic_maptype = arg;
+
+	uint64_t offset = sme->sme_offset;
+	uint64_t size = sme->sme_run;
+	uint64_t vdev_id = sme->sme_vdev;
+
+	vdev_t *vd = vdev_lookup_top(spa, vdev_id);
+
+	/* skip indirect vdevs */
+	if (!vdev_is_concrete(vd))
+		return (0);
+
+	metaslab_t *ms = vd->vdev_ms[offset >> vd->vdev_ms_shift];
+
+	ASSERT(sme->sme_type == SM_ALLOC || sme->sme_type == SM_FREE);
+	ASSERT(*uic_maptype == SM_ALLOC || *uic_maptype == SM_FREE);
+
+	if (txg < metaslab_unflushed_txg(ms))
+		return (0);
+
+	if (*uic_maptype == sme->sme_type)
+		range_tree_add(ms->ms_allocatable, offset, size);
+	else
+		range_tree_remove(ms->ms_allocatable, offset, size);
+
+	return (0);
+}
+
+static void
+load_unflushed_to_ms_allocatables(spa_t *spa, maptype_t maptype)
+{
+	iterate_through_spacemap_logs(spa, load_unflushed_cb, &maptype);
+}
+
 static void
 load_concrete_ms_allocatable_trees(spa_t *spa, maptype_t maptype)
 {
@@ -4093,7 +4293,7 @@ load_concrete_ms_allocatable_trees(spa_t *spa, maptype_t maptype)
 			    (longlong_t)vd->vdev_ms_count);

 			mutex_enter(&msp->ms_lock);
-			metaslab_unload(msp);
+			range_tree_vacate(msp->ms_allocatable, NULL, NULL);

 			/*
 			 * We don't want to spend the CPU manipulating the
@@ -4110,6 +4310,8 @@ load_concrete_ms_allocatable_trees(spa_t *spa, maptype_t maptype)
 			mutex_exit(&msp->ms_lock);
 		}
 	}
+
+	load_unflushed_to_ms_allocatables(spa, maptype);
 }

 /*
@@ -4124,7 +4326,7 @@ load_indirect_ms_allocatable_tree(vdev_t *vd, metaslab_t *msp,
 	vdev_indirect_mapping_t *vim = vd->vdev_indirect_mapping;

 	mutex_enter(&msp->ms_lock);
-	metaslab_unload(msp);
+	range_tree_vacate(msp->ms_allocatable, NULL, NULL);

 	/*
 	 * We don't want to spend the CPU manipulating the
@@ -4383,7 +4585,6 @@ zdb_leak_fini(spa_t *spa, zdb_cb_t *zcb)
 				range_tree_vacate(msp->ms_allocatable,
 				    zdb_leak, vd);
 			}
-
 			if (msp->ms_loaded) {
 				msp->ms_loaded = B_FALSE;
 			}
@@ -4520,7 +4721,8 @@ dump_block_stats(spa_t *spa)
 	total_alloc = norm_alloc +
 	    metaslab_class_get_alloc(spa_log_class(spa)) +
 	    metaslab_class_get_alloc(spa_special_class(spa)) +
-	    metaslab_class_get_alloc(spa_dedup_class(spa));
+	    metaslab_class_get_alloc(spa_dedup_class(spa)) +
+	    get_unflushed_alloc_space(spa);
 	total_found = tzb->zb_asize - zcb.zcb_dedup_asize +
 	    zcb.zcb_removing_size + zcb.zcb_checkpoint_size;

@@ -5392,12 +5594,25 @@ mos_obj_refd_multiple(uint64_t obj)
 		range_tree_add(mos_refd_objs, obj, 1);
 }

+static void
+mos_leak_vdev_top_zap(vdev_t *vd)
+{
+	uint64_t ms_flush_data_obj;
+	int error = zap_lookup(spa_meta_objset(vd->vdev_spa),
+	    vd->vdev_top_zap, VDEV_TOP_ZAP_MS_UNFLUSHED_PHYS_TXGS,
+	    sizeof (ms_flush_data_obj), 1, &ms_flush_data_obj);
+	if (error == ENOENT)
+		return;
+	ASSERT0(error);
+
+	mos_obj_refd(ms_flush_data_obj);
+}
+
 static void
 mos_leak_vdev(vdev_t *vd)
 {
 	mos_obj_refd(vd->vdev_dtl_object);
 	mos_obj_refd(vd->vdev_ms_array);
-	mos_obj_refd(vd->vdev_top_zap);
 	mos_obj_refd(vd->vdev_indirect_config.vic_births_object);
 	mos_obj_refd(vd->vdev_indirect_config.vic_mapping_object);
 	mos_obj_refd(vd->vdev_leaf_zap);
@@ -5415,11 +5630,33 @@ mos_leak_vdev(vdev_t *vd)
 		mos_obj_refd(space_map_object(ms->ms_sm));
 	}

+	if (vd->vdev_top_zap != 0) {
+		mos_obj_refd(vd->vdev_top_zap);
+		mos_leak_vdev_top_zap(vd);
+	}
+
 	for (uint64_t c = 0; c < vd->vdev_children; c++) {
 		mos_leak_vdev(vd->vdev_child[c]);
 	}
 }

+static void
+mos_leak_log_spacemaps(spa_t *spa)
+{
+	uint64_t spacemap_zap;
+	int error = zap_lookup(spa_meta_objset(spa),
+	    DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_LOG_SPACEMAP_ZAP,
+	    sizeof (spacemap_zap), 1, &spacemap_zap);
+	if (error == ENOENT)
+		return;
+	ASSERT0(error);
+
+	mos_obj_refd(spacemap_zap);
+	for (spa_log_sm_t *sls = avl_first(&spa->spa_sm_logs_by_txg);
+	    sls; sls = AVL_NEXT(&spa->spa_sm_logs_by_txg, sls))
+		mos_obj_refd(sls->sls_sm_obj);
+}
+
 static int
 dump_mos_leaks(spa_t *spa)
 {
@@ -5451,6 +5688,10 @@ dump_mos_leaks(spa_t *spa)
 	mos_obj_refd(spa->spa_l2cache.sav_object);
 	mos_obj_refd(spa->spa_spares.sav_object);

+	if (spa->spa_syncing_log_sm != NULL)
+		mos_obj_refd(spa->spa_syncing_log_sm->sm_object);
+	mos_leak_log_spacemaps(spa);
+
 	mos_obj_refd(spa->spa_condensing_indirect_phys.
 	    scip_next_mapping_object);
 	mos_obj_refd(spa->spa_condensing_indirect_phys.
@@ -5528,6 +5769,79 @@ dump_mos_leaks(spa_t *spa)
 	return (rv);
 }

+typedef struct log_sm_obsolete_stats_arg {
+	uint64_t lsos_current_txg;
+
+	uint64_t lsos_total_entries;
+	uint64_t lsos_valid_entries;
+
+	uint64_t lsos_sm_entries;
+	uint64_t lsos_valid_sm_entries;
+} log_sm_obsolete_stats_arg_t;
+
+static int
+log_spacemap_obsolete_stats_cb(spa_t *spa, space_map_entry_t *sme,
+    uint64_t txg, void *arg)
+{
+	log_sm_obsolete_stats_arg_t *lsos = arg;
+
+	uint64_t offset = sme->sme_offset;
+	uint64_t vdev_id = sme->sme_vdev;
+
+	if (lsos->lsos_current_txg == 0) {
+		/* this is the first log */
+		lsos->lsos_current_txg = txg;
+	} else if (lsos->lsos_current_txg < txg) {
+		/* we just changed log - print stats and reset */
+		(void) printf("%-8llu valid entries out of %-8llu - txg %llu\n",
+		    (u_longlong_t)lsos->lsos_valid_sm_entries,
+		    (u_longlong_t)lsos->lsos_sm_entries,
+		    (u_longlong_t)lsos->lsos_current_txg);
+		lsos->lsos_valid_sm_entries = 0;
+		lsos->lsos_sm_entries = 0;
+		lsos->lsos_current_txg = txg;
+	}
+	ASSERT3U(lsos->lsos_current_txg, ==, txg);
+
+	lsos->lsos_sm_entries++;
+	lsos->lsos_total_entries++;
+
+	vdev_t *vd = vdev_lookup_top(spa, vdev_id);
+	if (!vdev_is_concrete(vd))
+		return (0);
+
+	metaslab_t *ms = vd->vdev_ms[offset >> vd->vdev_ms_shift];
+	ASSERT(sme->sme_type == SM_ALLOC || sme->sme_type == SM_FREE);
+
+	if (txg < metaslab_unflushed_txg(ms))
+		return (0);
+	lsos->lsos_valid_sm_entries++;
+	lsos->lsos_valid_entries++;
+	return (0);
+}
+
+static void
+dump_log_spacemap_obsolete_stats(spa_t *spa)
+{
+	log_sm_obsolete_stats_arg_t lsos;
+	bzero(&lsos, sizeof (lsos));
+
+	(void) printf("Log Space Map Obsolete Entry Statistics:\n");
+
+	iterate_through_spacemap_logs(spa,
+	    log_spacemap_obsolete_stats_cb, &lsos);
+
+	/* print stats for latest log */
+	(void) printf("%-8llu valid entries out of %-8llu - txg %llu\n",
+	    (u_longlong_t)lsos.lsos_valid_sm_entries,
+	    (u_longlong_t)lsos.lsos_sm_entries,
+	    (u_longlong_t)lsos.lsos_current_txg);
+
+	(void) printf("%-8llu valid entries out of %-8llu - total\n\n",
+	    (u_longlong_t)lsos.lsos_valid_entries,
+	    (u_longlong_t)lsos.lsos_total_entries);
+}
+
 static void
 dump_zpool(spa_t *spa)
 {
@@ -5557,6 +5871,10 @@ dump_zpool(spa_t *spa)
 		dump_metaslabs(spa);
 	if (dump_opt['M'])
 		dump_metaslab_groups(spa);
+	if (dump_opt['d'] > 2 || dump_opt['m']) {
+		dump_log_spacemaps(spa);
+		dump_log_spacemap_obsolete_stats(spa);
+	}

 	if (dump_opt['d'] || dump_opt['i']) {
 		spa_feature_t f;
@@ -5635,9 +5953,8 @@ dump_zpool(spa_t *spa)
 			}
 		}

-		if (rc == 0) {
+		if (rc == 0)
 			rc = verify_device_removal_feature_counts(spa);
-		}
 	}

 	if (rc == 0 && (dump_opt['b'] || dump_opt['c']))