/* * CDDL HEADER START * * The contents of this file are subject to the terms of the * Common Development and Distribution License (the "License"). * You may not use this file except in compliance with the License. * * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE * or http://www.opensolaris.org/os/licensing. * See the License for the specific language governing permissions * and limitations under the License. * * When distributing Covered Code, include this CDDL HEADER in each * file and include the License file at usr/src/OPENSOLARIS.LICENSE. * If applicable, add the following below this CDDL HEADER, with the * fields enclosed by brackets "[]" replaced with your own identifying * information: Portions Copyright [yyyy] [name of copyright owner] * * CDDL HEADER END */ /* * Copyright (c) 2018, 2019 by Delphix. All rights reserved. */ #include <sys/dmu_objset.h> #include <sys/metaslab.h> #include <sys/metaslab_impl.h> #include <sys/spa.h> #include <sys/spa_impl.h> #include <sys/spa_log_spacemap.h> #include <sys/vdev_impl.h> #include <sys/zap.h> /* * Log Space Maps * * Log space maps are an optimization in ZFS metadata allocations for pools * whose workloads are primarily random-writes. Random-write workloads are also * typically random-free, meaning that they are freeing from locations scattered * throughout the pool. This means that each TXG we will have to append some * FREE records to almost every metaslab. With log space maps, we hold their * changes in memory and log them altogether in one pool-wide space map on-disk * for persistence. As more blocks are accumulated in the log space maps and * more unflushed changes are accounted in memory, we flush a selected group * of metaslabs every TXG to relieve memory pressure and potential overheads * when loading the pool. Flushing a metaslab to disk relieves memory as we * flush any unflushed changes from memory to disk (i.e. the metaslab's space * map) and saves import time by making old log space maps obsolete and * eventually destroying them. [A log space map is said to be obsolete when all * its entries have made it to their corresponding metaslab space maps]. * * == On disk data structures used == * * - The pool has a new feature flag and a new entry in the MOS. The feature * is activated when we create the first log space map and remains active * for the lifetime of the pool. The new entry in the MOS Directory [refer * to DMU_POOL_LOG_SPACEMAP_ZAP] is populated with a ZAP whose key-value * pairs are of the form <key: txg, value: log space map object for that txg>. * This entry is our on-disk reference of the log space maps that exist in * the pool for each TXG and it is used during import to load all the * metaslab unflushed changes in memory. To see how this structure is first * created and later populated refer to spa_generate_syncing_log_sm(). To see * how it is used during import time refer to spa_ld_log_sm_metadata(). * * - Each vdev has a new entry in its vdev_top_zap (see field * VDEV_TOP_ZAP_MS_UNFLUSHED_PHYS_TXGS) which holds the msp_unflushed_txg of * each metaslab in this vdev. This field is the on-disk counterpart of the * in-memory field ms_unflushed_txg which tells us from which TXG and onwards * the metaslab haven't had its changes flushed. During import, we use this * to ignore any entries in the space map log that are for this metaslab but * from a TXG before msp_unflushed_txg. At that point, we also populate its * in-memory counterpart and from there both fields are updated every time * we flush that metaslab. * * - A space map is created every TXG and, during that TXG, it is used to log * all incoming changes (the log space map). When created, the log space map * is referenced in memory by spa_syncing_log_sm and its object ID is inserted * to the space map ZAP mentioned above. The log space map is closed at the * end of the TXG and will be destroyed when it becomes fully obsolete. We * know when a log space map has become obsolete by looking at the oldest * (and smallest) ms_unflushed_txg in the pool. If the value of that is bigger * than the log space map's TXG, then it means that there is no metaslab who * doesn't have the changes from that log and we can therefore destroy it. * [see spa_cleanup_old_sm_logs()]. * * == Important in-memory structures == * * - The per-spa field spa_metaslabs_by_flushed sorts all the metaslabs in * the pool by their ms_unflushed_txg field. It is primarily used for three * reasons. First of all, it is used during flushing where we try to flush * metaslabs in-order from the oldest-flushed to the most recently flushed * every TXG. Secondly, it helps us to lookup the ms_unflushed_txg of the * oldest flushed metaslab to distinguish which log space maps have become * obsolete and which ones are still relevant. Finally it tells us which * metaslabs have unflushed changes in a pool where this feature was just * enabled, as we don't immediately add all of the pool's metaslabs but we * add them over time as they go through metaslab_sync(). The reason that * we do that is to ease these pools into the behavior of the flushing * algorithm (described later on). * * - The per-spa field spa_sm_logs_by_txg can be thought as the in-memory * counterpart of the space map ZAP mentioned above. It's an AVL tree whose * nodes represent the log space maps in the pool. This in-memory * representation of log space maps in the pool sorts the log space maps by * the TXG that they were created (which is also the TXG of their unflushed * changes). It also contains the following extra information for each * space map: * [1] The number of metaslabs that were last flushed on that TXG. This is * important because if that counter is zero and this is the oldest * log then it means that it is also obsolete. * [2] The number of blocks of that space map. This field is used by the * block heuristic of our flushing algorithm (described later on). * It represents how many blocks of metadata changes ZFS had to write * to disk for that TXG. * * - The per-spa field spa_log_summary is a list of entries that summarizes * the metaslab and block counts of all the nodes of the spa_sm_logs_by_txg * AVL tree mentioned above. The reason this exists is that our flushing * algorithm (described later) tries to estimate how many metaslabs to flush * in each TXG by iterating over all the log space maps and looking at their * block counts. Summarizing that information means that don't have to * iterate through each space map, minimizing the runtime overhead of the * flushing algorithm which would be induced in syncing context. In terms of * implementation the log summary is used as a queue: * * we modify or pop entries from its head when we flush metaslabs * * we modify or append entries to its tail when we sync changes. * * - Each metaslab has two new range trees that hold its unflushed changes, * ms_unflushed_allocs and ms_unflushed_frees. These are always disjoint. * * == Flushing algorithm == * * The decision of how many metaslabs to flush on a give TXG is guided by * two heuristics: * * [1] The memory heuristic - * We keep track of the memory used by the unflushed trees from all the * metaslabs [see sus_memused of spa_unflushed_stats] and we ensure that it * stays below a certain threshold which is determined by an arbitrary hard * limit and an arbitrary percentage of the system's memory [see * spa_log_exceeds_memlimit()]. When we see that the memory usage of the * unflushed changes are passing that threshold, we flush metaslabs, which * empties their unflushed range trees, reducing the memory used. * * [2] The block heuristic - * We try to keep the total number of blocks in the log space maps in check * so the log doesn't grow indefinitely and we don't induce a lot of overhead * when loading the pool. At the same time we don't want to flush a lot of * metaslabs too often as this would defeat the purpose of the log space map. * As a result we set a limit in the amount of blocks that we think it's * acceptable for the log space maps to have and try not to cross it. * [see sus_blocklimit from spa_unflushed_stats]. * * In order to stay below the block limit every TXG we have to estimate how * many metaslabs we need to flush based on the current rate of incoming blocks * and our history of log space map blocks. The main idea here is to answer * the question of how many metaslabs do we need to flush in order to get rid * at least an X amount of log space map blocks. We can answer this question * by iterating backwards from the oldest log space map to the newest one * and looking at their metaslab and block counts. At this point the log summary * mentioned above comes handy as it reduces the amount of things that we have * to iterate (even though it may reduce the preciseness of our estimates due * to its aggregation of data). So with that in mind, we project the incoming * rate of the current TXG into the future and attempt to approximate how many * metaslabs would we need to flush from now in order to avoid exceeding our * block limit in different points in the future (granted that we would keep * flushing the same number of metaslabs for every TXG). Then we take the * maximum number from all these estimates to be on the safe side. For the * exact implementation details of algorithm refer to * spa_estimate_metaslabs_to_flush. */ /* * This is used as the block size for the space maps used for the * log space map feature. These space maps benefit from a bigger * block size as we expect to be writing a lot of data to them at * once. */ unsigned long zfs_log_sm_blksz = 1ULL << 17; /* * Percentage of the overall system’s memory that ZFS allows to be * used for unflushed changes (e.g. the sum of size of all the nodes * in the unflushed trees). * * Note that this value is calculated over 1000000 for finer granularity * (thus the _ppm suffix; reads as "parts per million"). As an example, * the default of 1000 allows 0.1% of memory to be used. */ unsigned long zfs_unflushed_max_mem_ppm = 1000; /* * Specific hard-limit in memory that ZFS allows to be used for * unflushed changes. */ unsigned long zfs_unflushed_max_mem_amt = 1ULL << 30; /* * The following tunable determines the number of blocks that can be used for * the log space maps. It is expressed as a percentage of the total number of * metaslabs in the pool (i.e. the default of 400 means that the number of log * blocks is capped at 4 times the number of metaslabs). * * This value exists to tune our flushing algorithm, with higher values * flushing metaslabs less often (doing less I/Os) per TXG versus lower values * flushing metaslabs more aggressively with the upside of saving overheads * when loading the pool. Another factor in this tradeoff is that flushing * less often can potentially lead to better utilization of the metaslab space * map's block size as we accumulate more changes per flush. * * Given that this tunable indirectly controls the flush rate (metaslabs * flushed per txg) and that's why making it a percentage in terms of the * number of metaslabs in the pool makes sense here. * * As a rule of thumb we default this tunable to 400% based on the following: * * 1] Assuming a constant flush rate and a constant incoming rate of log blocks * it is reasonable to expect that the amount of obsolete entries changes * linearly from txg to txg (e.g. the oldest log should have the most * obsolete entries, and the most recent one the least). With this we could * say that, at any given time, about half of the entries in the whole space * map log are obsolete. Thus for every two entries for a metaslab in the * log space map, only one of them is valid and actually makes it to the * metaslab's space map. * [factor of 2] * 2] Each entry in the log space map is guaranteed to be two words while * entries in metaslab space maps are generally single-word. * [an extra factor of 2 - 400% overall] * 3] Even if [1] and [2] are slightly less than 2 each, we haven't taken into * account any consolidation of segments from the log space map to the * unflushed range trees nor their history (e.g. a segment being allocated, * then freed, then allocated again means 3 log space map entries but 0 * metaslab space map entries). Depending on the workload, we've seen ~1.8 * non-obsolete log space map entries per metaslab entry, for a total of * ~600%. Since most of these estimates though are workload dependent, we * default on 400% to be conservative. * * Thus we could say that even in the worst * case of [1] and [2], the factor should end up being 4. * * That said, regardless of the number of metaslabs in the pool we need to * provide upper and lower bounds for the log block limit. * [see zfs_unflushed_log_block_{min,max}] */ unsigned long zfs_unflushed_log_block_pct = 400; /* * If the number of metaslabs is small and our incoming rate is high, we could * get into a situation that we are flushing all our metaslabs every TXG. Thus * we always allow at least this many log blocks. */ unsigned long zfs_unflushed_log_block_min = 1000; /* * If the log becomes too big, the import time of the pool can take a hit in * terms of performance. Thus we have a hard limit in the size of the log in * terms of blocks. */ unsigned long zfs_unflushed_log_block_max = (1ULL << 18); /* * Max # of rows allowed for the log_summary. The tradeoff here is accuracy and * stability of the flushing algorithm (longer summary) vs its runtime overhead * (smaller summary is faster to traverse). */ unsigned long zfs_max_logsm_summary_length = 10; /* * Tunable that sets the lower bound on the metaslabs to flush every TXG. * * Setting this to 0 has no effect since if the pool is idle we won't even be * creating log space maps and therefore we won't be flushing. On the other * hand if the pool has any incoming workload our block heuristic will start * flushing metaslabs anyway. * * The point of this tunable is to be used in extreme cases where we really * want to flush more metaslabs than our adaptable heuristic plans to flush. */ unsigned long zfs_min_metaslabs_to_flush = 1; /* * Tunable that specifies how far in the past do we want to look when trying to * estimate the incoming log blocks for the current TXG. * * Setting this too high may not only increase runtime but also minimize the * effect of the incoming rates from the most recent TXGs as we take the * average over all the blocks that we walk * [see spa_estimate_incoming_log_blocks]. */ unsigned long zfs_max_log_walking = 5; /* * This tunable exists solely for testing purposes. It ensures that the log * spacemaps are not flushed and destroyed during export in order for the * relevant log spacemap import code paths to be tested (effectively simulating * a crash). */ int zfs_keep_log_spacemaps_at_export = 0; static uint64_t spa_estimate_incoming_log_blocks(spa_t *spa) { ASSERT3U(spa_sync_pass(spa), ==, 1); uint64_t steps = 0, sum = 0; for (spa_log_sm_t *sls = avl_last(&spa->spa_sm_logs_by_txg); sls != NULL && steps < zfs_max_log_walking; sls = AVL_PREV(&spa->spa_sm_logs_by_txg, sls)) { if (sls->sls_txg == spa_syncing_txg(spa)) { /* * skip the log created in this TXG as this would * make our estimations inaccurate. */ continue; } sum += sls->sls_nblocks; steps++; } return ((steps > 0) ? DIV_ROUND_UP(sum, steps) : 0); } uint64_t spa_log_sm_blocklimit(spa_t *spa) { return (spa->spa_unflushed_stats.sus_blocklimit); } void spa_log_sm_set_blocklimit(spa_t *spa) { if (!spa_feature_is_active(spa, SPA_FEATURE_LOG_SPACEMAP)) { ASSERT0(spa_log_sm_blocklimit(spa)); return; } uint64_t calculated_limit = (spa_total_metaslabs(spa) * zfs_unflushed_log_block_pct) / 100; spa->spa_unflushed_stats.sus_blocklimit = MIN(MAX(calculated_limit, zfs_unflushed_log_block_min), zfs_unflushed_log_block_max); } uint64_t spa_log_sm_nblocks(spa_t *spa) { return (spa->spa_unflushed_stats.sus_nblocks); } /* * Ensure that the in-memory log space map structures and the summary * have the same block and metaslab counts. */ static void spa_log_summary_verify_counts(spa_t *spa) { ASSERT(spa_feature_is_active(spa, SPA_FEATURE_LOG_SPACEMAP)); if ((zfs_flags & ZFS_DEBUG_LOG_SPACEMAP) == 0) return; uint64_t ms_in_avl = avl_numnodes(&spa->spa_metaslabs_by_flushed); uint64_t ms_in_summary = 0, blk_in_summary = 0; for (log_summary_entry_t *e = list_head(&spa->spa_log_summary); e; e = list_next(&spa->spa_log_summary, e)) { ms_in_summary += e->lse_mscount; blk_in_summary += e->lse_blkcount; } uint64_t ms_in_logs = 0, blk_in_logs = 0; 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)) { ms_in_logs += sls->sls_mscount; blk_in_logs += sls->sls_nblocks; } VERIFY3U(ms_in_logs, ==, ms_in_summary); VERIFY3U(ms_in_logs, ==, ms_in_avl); VERIFY3U(blk_in_logs, ==, blk_in_summary); VERIFY3U(blk_in_logs, ==, spa_log_sm_nblocks(spa)); } static boolean_t summary_entry_is_full(spa_t *spa, log_summary_entry_t *e) { uint64_t blocks_per_row = MAX(1, DIV_ROUND_UP(spa_log_sm_blocklimit(spa), zfs_max_logsm_summary_length)); return (blocks_per_row <= e->lse_blkcount); } /* * Update the log summary information to reflect the fact that a metaslab * was flushed or destroyed (e.g due to device removal or pool export/destroy). * * We typically flush the oldest flushed metaslab so the first (and oldest) * entry of the summary is updated. However if that metaslab is getting loaded * we may flush the second oldest one which may be part of an entry later in * the summary. Moreover, if we call into this function from metaslab_fini() * the metaslabs probably won't be ordered by ms_unflushed_txg. Thus we ask * for a txg as an argument so we can locate the appropriate summary entry for * the metaslab. */ void spa_log_summary_decrement_mscount(spa_t *spa, uint64_t txg) { /* * We don't track summary data for read-only pools and this function * can be called from metaslab_fini(). In that case return immediately. */ if (!spa_writeable(spa)) return; log_summary_entry_t *target = NULL; for (log_summary_entry_t *e = list_head(&spa->spa_log_summary); e != NULL; e = list_next(&spa->spa_log_summary, e)) { if (e->lse_start > txg) break; target = e; } if (target == NULL || target->lse_mscount == 0) { /* * We didn't find a summary entry for this metaslab. We must be * at the teardown of a spa_load() attempt that got an error * while reading the log space maps. */ VERIFY3S(spa_load_state(spa), ==, SPA_LOAD_ERROR); return; } target->lse_mscount--; } /* * Update the log summary information to reflect the fact that we destroyed * old log space maps. Since we can only destroy the oldest log space maps, * we decrement the block count of the oldest summary entry and potentially * destroy it when that count hits 0. * * This function is called after a metaslab is flushed and typically that * metaslab is the oldest flushed, which means that this function will * typically decrement the block count of the first entry of the summary and * potentially free it if the block count gets to zero (its metaslab count * should be zero too at that point). * * There are certain scenarios though that don't work exactly like that so we * need to account for them: * * Scenario [1]: It is possible that after we flushed the oldest flushed * metaslab and we destroyed the oldest log space map, more recent logs had 0 * metaslabs pointing to them so we got rid of them too. This can happen due * to metaslabs being destroyed through device removal, or because the oldest * flushed metaslab was loading but we kept flushing more recently flushed * metaslabs due to the memory pressure of unflushed changes. Because of that, * we always iterate from the beginning of the summary and if blocks_gone is * bigger than the block_count of the current entry we free that entry (we * expect its metaslab count to be zero), we decrement blocks_gone and on to * the next entry repeating this procedure until blocks_gone gets decremented * to 0. Doing this also works for the typical case mentioned above. * * Scenario [2]: The oldest flushed metaslab isn't necessarily accounted by * the first (and oldest) entry in the summary. If the first few entries of * the summary were only accounting metaslabs from a device that was just * removed, then the current oldest flushed metaslab could be accounted by an * entry somewhere in the middle of the summary. Moreover flushing that * metaslab will destroy all the log space maps older than its ms_unflushed_txg * because they became obsolete after the removal. Thus, iterating as we did * for scenario [1] works out for this case too. * * Scenario [3]: At times we decide to flush all the metaslabs in the pool * in one TXG (either because we are exporting the pool or because our flushing * heuristics decided to do so). When that happens all the log space maps get * destroyed except the one created for the current TXG which doesn't have * any log blocks yet. As log space maps get destroyed with every metaslab that * we flush, entries in the summary are also destroyed. This brings a weird * corner-case when we flush the last metaslab and the log space map of the * current TXG is in the same summary entry with other log space maps that * are older. When that happens we are eventually left with this one last * summary entry whose blocks are gone (blocks_gone equals the entry's block * count) but its metaslab count is non-zero (because it accounts all the * metaslabs in the pool as they all got flushed). Under this scenario we can't * free this last summary entry as it's referencing all the metaslabs in the * pool and its block count will get incremented at the end of this sync (when * we close the syncing log space map). Thus we just decrement its current * block count and leave it alone. In the case that the pool gets exported, * its metaslab count will be decremented over time as we call metaslab_fini() * for all the metaslabs in the pool and the entry will be freed at * spa_unload_log_sm_metadata(). */ void spa_log_summary_decrement_blkcount(spa_t *spa, uint64_t blocks_gone) { for (log_summary_entry_t *e = list_head(&spa->spa_log_summary); e != NULL; e = list_head(&spa->spa_log_summary)) { if (e->lse_blkcount > blocks_gone) { /* * Assert that we stopped at an entry that is not * obsolete. */ ASSERT(e->lse_mscount != 0); e->lse_blkcount -= blocks_gone; blocks_gone = 0; break; } else if (e->lse_mscount == 0) { /* remove obsolete entry */ blocks_gone -= e->lse_blkcount; list_remove(&spa->spa_log_summary, e); kmem_free(e, sizeof (log_summary_entry_t)); } else { /* Verify that this is scenario [3] mentioned above. */ VERIFY3U(blocks_gone, ==, e->lse_blkcount); /* * Assert that this is scenario [3] further by ensuring * that this is the only entry in the summary. */ VERIFY3P(e, ==, list_tail(&spa->spa_log_summary)); ASSERT3P(e, ==, list_head(&spa->spa_log_summary)); blocks_gone = e->lse_blkcount = 0; break; } } /* * Ensure that there is no way we are trying to remove more blocks * than the # of blocks in the summary. */ ASSERT0(blocks_gone); } void spa_log_sm_decrement_mscount(spa_t *spa, uint64_t txg) { spa_log_sm_t target = { .sls_txg = txg }; spa_log_sm_t *sls = avl_find(&spa->spa_sm_logs_by_txg, &target, NULL); if (sls == NULL) { /* * We must be at the teardown of a spa_load() attempt that * got an error while reading the log space maps. */ VERIFY3S(spa_load_state(spa), ==, SPA_LOAD_ERROR); return; } ASSERT(sls->sls_mscount > 0); sls->sls_mscount--; } void spa_log_sm_increment_current_mscount(spa_t *spa) { spa_log_sm_t *last_sls = avl_last(&spa->spa_sm_logs_by_txg); ASSERT3U(last_sls->sls_txg, ==, spa_syncing_txg(spa)); last_sls->sls_mscount++; } static void summary_add_data(spa_t *spa, uint64_t txg, uint64_t metaslabs_flushed, uint64_t nblocks) { log_summary_entry_t *e = list_tail(&spa->spa_log_summary); if (e == NULL || summary_entry_is_full(spa, e)) { e = kmem_zalloc(sizeof (log_summary_entry_t), KM_SLEEP); e->lse_start = txg; list_insert_tail(&spa->spa_log_summary, e); } ASSERT3U(e->lse_start, <=, txg); e->lse_mscount += metaslabs_flushed; e->lse_blkcount += nblocks; } static void spa_log_summary_add_incoming_blocks(spa_t *spa, uint64_t nblocks) { summary_add_data(spa, spa_syncing_txg(spa), 0, nblocks); } void spa_log_summary_add_flushed_metaslab(spa_t *spa) { summary_add_data(spa, spa_syncing_txg(spa), 1, 0); } /* * This function attempts to estimate how many metaslabs should * we flush to satisfy our block heuristic for the log spacemap * for the upcoming TXGs. * * Specifically, it first tries to estimate the number of incoming * blocks in this TXG. Then by projecting that incoming rate to * future TXGs and using the log summary, it figures out how many * flushes we would need to do for future TXGs individually to * stay below our block limit and returns the maximum number of * flushes from those estimates. */ static uint64_t spa_estimate_metaslabs_to_flush(spa_t *spa) { ASSERT(spa_feature_is_active(spa, SPA_FEATURE_LOG_SPACEMAP)); ASSERT3U(spa_sync_pass(spa), ==, 1); ASSERT(spa_log_sm_blocklimit(spa) != 0); /* * This variable contains the incoming rate that will be projected * and used for our flushing estimates in the future. */ uint64_t incoming = spa_estimate_incoming_log_blocks(spa); /* * At any point in time this variable tells us how many * TXGs in the future we are so we can make our estimations. */ uint64_t txgs_in_future = 1; /* * This variable tells us how much room do we have until we hit * our limit. When it goes negative, it means that we've exceeded * our limit and we need to flush. * * Note that since we start at the first TXG in the future (i.e. * txgs_in_future starts from 1) we already decrement this * variable by the incoming rate. */ int64_t available_blocks = spa_log_sm_blocklimit(spa) - spa_log_sm_nblocks(spa) - incoming; /* * This variable tells us the total number of flushes needed to * keep the log size within the limit when we reach txgs_in_future. */ uint64_t total_flushes = 0; /* Holds the current maximum of our estimates so far. */ uint64_t max_flushes_pertxg = MIN(avl_numnodes(&spa->spa_metaslabs_by_flushed), zfs_min_metaslabs_to_flush); /* * For our estimations we only look as far in the future * as the summary allows us. */ for (log_summary_entry_t *e = list_head(&spa->spa_log_summary); e; e = list_next(&spa->spa_log_summary, e)) { /* * If there is still room before we exceed our limit * then keep skipping TXGs accumulating more blocks * based on the incoming rate until we exceed it. */ if (available_blocks >= 0) { uint64_t skip_txgs = (available_blocks / incoming) + 1; available_blocks -= (skip_txgs * incoming); txgs_in_future += skip_txgs; ASSERT3S(available_blocks, >=, -incoming); } /* * At this point we're far enough into the future where * the limit was just exceeded and we flush metaslabs * based on the current entry in the summary, updating * our available_blocks. */ ASSERT3S(available_blocks, <, 0); available_blocks += e->lse_blkcount; total_flushes += e->lse_mscount; /* * Keep the running maximum of the total_flushes that * we've done so far over the number of TXGs in the * future that we are. The idea here is to estimate * the average number of flushes that we should do * every TXG so that when we are that many TXGs in the * future we stay under the limit. */ max_flushes_pertxg = MAX(max_flushes_pertxg, DIV_ROUND_UP(total_flushes, txgs_in_future)); ASSERT3U(avl_numnodes(&spa->spa_metaslabs_by_flushed), >=, max_flushes_pertxg); } return (max_flushes_pertxg); } uint64_t spa_log_sm_memused(spa_t *spa) { return (spa->spa_unflushed_stats.sus_memused); } static boolean_t spa_log_exceeds_memlimit(spa_t *spa) { if (spa_log_sm_memused(spa) > zfs_unflushed_max_mem_amt) return (B_TRUE); uint64_t system_mem_allowed = ((physmem * PAGESIZE) * zfs_unflushed_max_mem_ppm) / 1000000; if (spa_log_sm_memused(spa) > system_mem_allowed) return (B_TRUE); return (B_FALSE); } boolean_t spa_flush_all_logs_requested(spa_t *spa) { return (spa->spa_log_flushall_txg != 0); } void spa_flush_metaslabs(spa_t *spa, dmu_tx_t *tx) { uint64_t txg = dmu_tx_get_txg(tx); if (spa_sync_pass(spa) != 1) return; if (!spa_feature_is_active(spa, SPA_FEATURE_LOG_SPACEMAP)) return; /* * If we don't have any metaslabs with unflushed changes * return immediately. */ if (avl_numnodes(&spa->spa_metaslabs_by_flushed) == 0) return; /* * During SPA export we leave a few empty TXGs to go by [see * spa_final_dirty_txg() to understand why]. For this specific * case, it is important to not flush any metaslabs as that * would dirty this TXG. * * That said, during one of these dirty TXGs that is less or * equal to spa_final_dirty(), spa_unload() will request that * we try to flush all the metaslabs for that TXG before * exporting the pool, thus we ensure that we didn't get a * request of flushing everything before we attempt to return * immediately. */ if (spa->spa_uberblock.ub_rootbp.blk_birth < txg && !dmu_objset_is_dirty(spa_meta_objset(spa), txg) && !spa_flush_all_logs_requested(spa)) return; /* * We need to generate a log space map before flushing because this * will set up the in-memory data (i.e. node in spa_sm_logs_by_txg) * for this TXG's flushed metaslab count (aka sls_mscount which is * manipulated in many ways down the metaslab_flush() codepath). * * That is not to say that we may generate a log space map when we * don't need it. If we are flushing metaslabs, that means that we * were going to write changes to disk anyway, so even if we were * not flushing, a log space map would have been created anyway in * metaslab_sync(). */ spa_generate_syncing_log_sm(spa, tx); /* * This variable tells us how many metaslabs we want to flush based * on the block-heuristic of our flushing algorithm (see block comment * of log space map feature). We also decrement this as we flush * metaslabs and attempt to destroy old log space maps. */ uint64_t want_to_flush; if (spa_flush_all_logs_requested(spa)) { ASSERT3S(spa_state(spa), ==, POOL_STATE_EXPORTED); want_to_flush = avl_numnodes(&spa->spa_metaslabs_by_flushed); } else { want_to_flush = spa_estimate_metaslabs_to_flush(spa); } ASSERT3U(avl_numnodes(&spa->spa_metaslabs_by_flushed), >=, want_to_flush); /* Used purely for verification purposes */ uint64_t visited = 0; /* * Ideally we would only iterate through spa_metaslabs_by_flushed * using only one variable (curr). We can't do that because * metaslab_flush() mutates position of curr in the AVL when * it flushes that metaslab by moving it to the end of the tree. * Thus we always keep track of the original next node of the * current node (curr) in another variable (next). */ metaslab_t *next = NULL; for (metaslab_t *curr = avl_first(&spa->spa_metaslabs_by_flushed); curr != NULL; curr = next) { next = AVL_NEXT(&spa->spa_metaslabs_by_flushed, curr); /* * If this metaslab has been flushed this txg then we've done * a full circle over the metaslabs. */ if (metaslab_unflushed_txg(curr) == txg) break; /* * If we are done flushing for the block heuristic and the * unflushed changes don't exceed the memory limit just stop. */ if (want_to_flush == 0 && !spa_log_exceeds_memlimit(spa)) break; mutex_enter(&curr->ms_sync_lock); mutex_enter(&curr->ms_lock); boolean_t flushed = metaslab_flush(curr, tx); mutex_exit(&curr->ms_lock); mutex_exit(&curr->ms_sync_lock); /* * If we failed to flush a metaslab (because it was loading), * then we are done with the block heuristic as it's not * possible to destroy any log space maps once you've skipped * a metaslab. In that case we just set our counter to 0 but * we continue looping in case there is still memory pressure * due to unflushed changes. Note that, flushing a metaslab * that is not the oldest flushed in the pool, will never * destroy any log space maps [see spa_cleanup_old_sm_logs()]. */ if (!flushed) { want_to_flush = 0; } else if (want_to_flush > 0) { want_to_flush--; } visited++; } ASSERT3U(avl_numnodes(&spa->spa_metaslabs_by_flushed), >=, visited); } /* * Close the log space map for this TXG and update the block counts * for the the log's in-memory structure and the summary. */ void spa_sync_close_syncing_log_sm(spa_t *spa) { if (spa_syncing_log_sm(spa) == NULL) return; ASSERT(spa_feature_is_active(spa, SPA_FEATURE_LOG_SPACEMAP)); spa_log_sm_t *sls = avl_last(&spa->spa_sm_logs_by_txg); ASSERT3U(sls->sls_txg, ==, spa_syncing_txg(spa)); sls->sls_nblocks = space_map_nblocks(spa_syncing_log_sm(spa)); spa->spa_unflushed_stats.sus_nblocks += sls->sls_nblocks; /* * Note that we can't assert that sls_mscount is not 0, * because there is the case where the first metaslab * in spa_metaslabs_by_flushed is loading and we were * not able to flush any metaslabs the current TXG. */ ASSERT(sls->sls_nblocks != 0); spa_log_summary_add_incoming_blocks(spa, sls->sls_nblocks); spa_log_summary_verify_counts(spa); space_map_close(spa->spa_syncing_log_sm); spa->spa_syncing_log_sm = NULL; /* * At this point we tried to flush as many metaslabs as we * can as the pool is getting exported. Reset the "flush all" * so the last few TXGs before closing the pool can be empty * (e.g. not dirty). */ if (spa_flush_all_logs_requested(spa)) { ASSERT3S(spa_state(spa), ==, POOL_STATE_EXPORTED); spa->spa_log_flushall_txg = 0; } } void spa_cleanup_old_sm_logs(spa_t *spa, dmu_tx_t *tx) { objset_t *mos = spa_meta_objset(spa); uint64_t spacemap_zap; int error = zap_lookup(mos, DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_LOG_SPACEMAP_ZAP, sizeof (spacemap_zap), 1, &spacemap_zap); if (error == ENOENT) { ASSERT(avl_is_empty(&spa->spa_sm_logs_by_txg)); return; } VERIFY0(error); metaslab_t *oldest = avl_first(&spa->spa_metaslabs_by_flushed); uint64_t oldest_flushed_txg = metaslab_unflushed_txg(oldest); /* Free all log space maps older than the oldest_flushed_txg. */ for (spa_log_sm_t *sls = avl_first(&spa->spa_sm_logs_by_txg); sls && sls->sls_txg < oldest_flushed_txg; sls = avl_first(&spa->spa_sm_logs_by_txg)) { ASSERT0(sls->sls_mscount); avl_remove(&spa->spa_sm_logs_by_txg, sls); space_map_free_obj(mos, sls->sls_sm_obj, tx); VERIFY0(zap_remove_int(mos, spacemap_zap, sls->sls_txg, tx)); spa->spa_unflushed_stats.sus_nblocks -= sls->sls_nblocks; kmem_free(sls, sizeof (spa_log_sm_t)); } } static spa_log_sm_t * spa_log_sm_alloc(uint64_t sm_obj, uint64_t txg) { spa_log_sm_t *sls = kmem_zalloc(sizeof (*sls), KM_SLEEP); sls->sls_sm_obj = sm_obj; sls->sls_txg = txg; return (sls); } void spa_generate_syncing_log_sm(spa_t *spa, dmu_tx_t *tx) { uint64_t txg = dmu_tx_get_txg(tx); objset_t *mos = spa_meta_objset(spa); if (spa_syncing_log_sm(spa) != NULL) return; if (!spa_feature_is_enabled(spa, SPA_FEATURE_LOG_SPACEMAP)) return; uint64_t spacemap_zap; int error = zap_lookup(mos, DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_LOG_SPACEMAP_ZAP, sizeof (spacemap_zap), 1, &spacemap_zap); if (error == ENOENT) { ASSERT(avl_is_empty(&spa->spa_sm_logs_by_txg)); error = 0; spacemap_zap = zap_create(mos, DMU_OTN_ZAP_METADATA, DMU_OT_NONE, 0, tx); VERIFY0(zap_add(mos, DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_LOG_SPACEMAP_ZAP, sizeof (spacemap_zap), 1, &spacemap_zap, tx)); spa_feature_incr(spa, SPA_FEATURE_LOG_SPACEMAP, tx); } VERIFY0(error); uint64_t sm_obj; ASSERT3U(zap_lookup_int_key(mos, spacemap_zap, txg, &sm_obj), ==, ENOENT); sm_obj = space_map_alloc(mos, zfs_log_sm_blksz, tx); VERIFY0(zap_add_int_key(mos, spacemap_zap, txg, sm_obj, tx)); avl_add(&spa->spa_sm_logs_by_txg, spa_log_sm_alloc(sm_obj, txg)); /* * We pass UINT64_MAX as the space map's representation size * and SPA_MINBLOCKSHIFT as the shift, to make the space map * accept any sorts of segments since there's no real advantage * to being more restrictive (given that we're already going * to be using 2-word entries). */ VERIFY0(space_map_open(&spa->spa_syncing_log_sm, mos, sm_obj, 0, UINT64_MAX, SPA_MINBLOCKSHIFT)); /* * If the log space map feature was just enabled, the blocklimit * has not yet been set. */ if (spa_log_sm_blocklimit(spa) == 0) spa_log_sm_set_blocklimit(spa); } /* * Find all the log space maps stored in the space map ZAP and sort * them by their TXG in spa_sm_logs_by_txg. */ static int spa_ld_log_sm_metadata(spa_t *spa) { int error; uint64_t spacemap_zap; ASSERT(avl_is_empty(&spa->spa_sm_logs_by_txg)); 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) { /* the space map ZAP doesn't exist yet */ return (0); } else if (error != 0) { spa_load_failed(spa, "spa_ld_log_sm_metadata(): failed at " "zap_lookup(DMU_POOL_DIRECTORY_OBJECT) [error %d]", error); return (error); } zap_cursor_t zc; zap_attribute_t za; for (zap_cursor_init(&zc, spa_meta_objset(spa), spacemap_zap); (error = zap_cursor_retrieve(&zc, &za)) == 0; zap_cursor_advance(&zc)) { uint64_t log_txg = zfs_strtonum(za.za_name, NULL); spa_log_sm_t *sls = spa_log_sm_alloc(za.za_first_integer, log_txg); avl_add(&spa->spa_sm_logs_by_txg, sls); } zap_cursor_fini(&zc); if (error != ENOENT) { spa_load_failed(spa, "spa_ld_log_sm_metadata(): failed at " "zap_cursor_retrieve(spacemap_zap) [error %d]", error); return (error); } for (metaslab_t *m = avl_first(&spa->spa_metaslabs_by_flushed); m; m = AVL_NEXT(&spa->spa_metaslabs_by_flushed, m)) { spa_log_sm_t target = { .sls_txg = metaslab_unflushed_txg(m) }; spa_log_sm_t *sls = avl_find(&spa->spa_sm_logs_by_txg, &target, NULL); /* * At this point if sls is zero it means that a bug occurred * in ZFS the last time the pool was open or earlier in the * import code path. In general, we would have placed a * VERIFY() here or in this case just let the kernel panic * with NULL pointer dereference when incrementing sls_mscount, * but since this is the import code path we can be a bit more * lenient. Thus, for DEBUG bits we always cause a panic, while * in production we log the error and just fail the import. */ ASSERT(sls != NULL); if (sls == NULL) { spa_load_failed(spa, "spa_ld_log_sm_metadata(): bug " "encountered: could not find log spacemap for " "TXG %ld [error %d]", metaslab_unflushed_txg(m), ENOENT); return (ENOENT); } sls->sls_mscount++; } return (0); } typedef struct spa_ld_log_sm_arg { spa_t *slls_spa; uint64_t slls_txg; } spa_ld_log_sm_arg_t; static int spa_ld_log_sm_cb(space_map_entry_t *sme, void *arg) { uint64_t offset = sme->sme_offset; uint64_t size = sme->sme_run; uint32_t vdev_id = sme->sme_vdev; spa_ld_log_sm_arg_t *slls = arg; spa_t *spa = slls->slls_spa; vdev_t *vd = vdev_lookup_top(spa, vdev_id); /* * If the vdev has been removed (i.e. it is indirect or a hole) * skip this entry. The contents of this vdev have already moved * elsewhere. */ if (!vdev_is_concrete(vd)) return (0); metaslab_t *ms = vd->vdev_ms[offset >> vd->vdev_ms_shift]; ASSERT(!ms->ms_loaded); /* * If we have already flushed entries for this TXG to this * metaslab's space map, then ignore it. Note that we flush * before processing any allocations/frees for that TXG, so * the metaslab's space map only has entries from *before* * the unflushed TXG. */ if (slls->slls_txg < metaslab_unflushed_txg(ms)) return (0); switch (sme->sme_type) { case SM_ALLOC: range_tree_remove_xor_add_segment(offset, offset + size, ms->ms_unflushed_frees, ms->ms_unflushed_allocs); break; case SM_FREE: range_tree_remove_xor_add_segment(offset, offset + size, ms->ms_unflushed_allocs, ms->ms_unflushed_frees); break; default: panic("invalid maptype_t"); break; } return (0); } static int spa_ld_log_sm_data(spa_t *spa) { int error = 0; /* * If we are not going to do any writes there is no need * to read the log space maps. */ if (!spa_writeable(spa)) return (0); ASSERT0(spa->spa_unflushed_stats.sus_nblocks); ASSERT0(spa->spa_unflushed_stats.sus_memused); hrtime_t read_logs_starttime = gethrtime(); /* this is a no-op when we don't have space map logs */ 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; error = space_map_open(&sm, spa_meta_objset(spa), sls->sls_sm_obj, 0, UINT64_MAX, SPA_MINBLOCKSHIFT); if (error != 0) { spa_load_failed(spa, "spa_ld_log_sm_data(): failed at " "space_map_open(obj=%llu) [error %d]", (u_longlong_t)sls->sls_sm_obj, error); goto out; } struct spa_ld_log_sm_arg vla = { .slls_spa = spa, .slls_txg = sls->sls_txg }; error = space_map_iterate(sm, space_map_length(sm), spa_ld_log_sm_cb, &vla); if (error != 0) { space_map_close(sm); spa_load_failed(spa, "spa_ld_log_sm_data(): failed " "at space_map_iterate(obj=%llu) [error %d]", (u_longlong_t)sls->sls_sm_obj, error); goto out; } ASSERT0(sls->sls_nblocks); sls->sls_nblocks = space_map_nblocks(sm); spa->spa_unflushed_stats.sus_nblocks += sls->sls_nblocks; summary_add_data(spa, sls->sls_txg, sls->sls_mscount, sls->sls_nblocks); space_map_close(sm); } hrtime_t read_logs_endtime = gethrtime(); spa_load_note(spa, "read %llu log space maps (%llu total blocks - blksz = %llu bytes) " "in %lld ms", (u_longlong_t)avl_numnodes(&spa->spa_sm_logs_by_txg), (u_longlong_t)spa_log_sm_nblocks(spa), (u_longlong_t)zfs_log_sm_blksz, (longlong_t)((read_logs_endtime - read_logs_starttime) / 1000000)); out: /* * Now that the metaslabs contain their unflushed changes: * [1] recalculate their actual allocated space * [2] recalculate their weights * [3] sum up the memory usage of their unflushed range trees * [4] optionally load them, if debug_load is set * * Note that even in the case where we get here because of an * error (e.g. error != 0), we still want to update the fields * below in order to have a proper teardown in spa_unload(). */ for (metaslab_t *m = avl_first(&spa->spa_metaslabs_by_flushed); m != NULL; m = AVL_NEXT(&spa->spa_metaslabs_by_flushed, m)) { mutex_enter(&m->ms_lock); m->ms_allocated_space = space_map_allocated(m->ms_sm) + range_tree_space(m->ms_unflushed_allocs) - range_tree_space(m->ms_unflushed_frees); vdev_t *vd = m->ms_group->mg_vd; metaslab_space_update(vd, m->ms_group->mg_class, range_tree_space(m->ms_unflushed_allocs), 0, 0); metaslab_space_update(vd, m->ms_group->mg_class, -range_tree_space(m->ms_unflushed_frees), 0, 0); ASSERT0(m->ms_weight & METASLAB_ACTIVE_MASK); metaslab_recalculate_weight_and_sort(m); spa->spa_unflushed_stats.sus_memused += metaslab_unflushed_changes_memused(m); if (metaslab_debug_load && m->ms_sm != NULL) { VERIFY0(metaslab_load(m)); metaslab_set_selected_txg(m, 0); } mutex_exit(&m->ms_lock); } return (error); } static int spa_ld_unflushed_txgs(vdev_t *vd) { spa_t *spa = vd->vdev_spa; objset_t *mos = spa_meta_objset(spa); if (vd->vdev_top_zap == 0) return (0); uint64_t object = 0; int error = zap_lookup(mos, vd->vdev_top_zap, VDEV_TOP_ZAP_MS_UNFLUSHED_PHYS_TXGS, sizeof (uint64_t), 1, &object); if (error == ENOENT) return (0); else if (error != 0) { spa_load_failed(spa, "spa_ld_unflushed_txgs(): failed at " "zap_lookup(vdev_top_zap=%llu) [error %d]", (u_longlong_t)vd->vdev_top_zap, error); return (error); } for (uint64_t m = 0; m < vd->vdev_ms_count; m++) { metaslab_t *ms = vd->vdev_ms[m]; ASSERT(ms != NULL); metaslab_unflushed_phys_t entry; uint64_t entry_size = sizeof (entry); uint64_t entry_offset = ms->ms_id * entry_size; error = dmu_read(mos, object, entry_offset, entry_size, &entry, 0); if (error != 0) { spa_load_failed(spa, "spa_ld_unflushed_txgs(): " "failed at dmu_read(obj=%llu) [error %d]", (u_longlong_t)object, error); return (error); } ms->ms_unflushed_txg = entry.msp_unflushed_txg; if (ms->ms_unflushed_txg != 0) { mutex_enter(&spa->spa_flushed_ms_lock); avl_add(&spa->spa_metaslabs_by_flushed, ms); mutex_exit(&spa->spa_flushed_ms_lock); } } return (0); } /* * Read all the log space map entries into their respective * metaslab unflushed trees and keep them sorted by TXG in the * SPA's metadata. In addition, setup all the metadata for the * memory and the block heuristics. */ int spa_ld_log_spacemaps(spa_t *spa) { int error; spa_log_sm_set_blocklimit(spa); for (uint64_t c = 0; c < spa->spa_root_vdev->vdev_children; c++) { vdev_t *vd = spa->spa_root_vdev->vdev_child[c]; error = spa_ld_unflushed_txgs(vd); if (error != 0) return (error); } error = spa_ld_log_sm_metadata(spa); if (error != 0) return (error); /* * Note: we don't actually expect anything to change at this point * but we grab the config lock so we don't fail any assertions * when using vdev_lookup_top(). */ spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER); error = spa_ld_log_sm_data(spa); spa_config_exit(spa, SCL_CONFIG, FTAG); return (error); }
