/* * 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) 2017 by Delphix. All rights reserved. */ /* * Storage Pool Checkpoint * * A storage pool checkpoint can be thought of as a pool-wide snapshot or * a stable version of extreme rewind that guarantees no blocks from the * checkpointed state will have been overwritten. It remembers the entire * state of the storage pool (e.g. snapshots, dataset names, etc..) from the * point that it was taken and the user can rewind back to that point even if * they applied destructive operations on their datasets or even enabled new * zpool on-disk features. If a pool has a checkpoint that is no longer * needed, the user can discard it. * * == On disk data structures used == * * - The pool has a new feature flag and a new entry in the MOS. The feature * flag is set to active when we create the checkpoint and remains active * until the checkpoint is fully discarded. The entry in the MOS config * (DMU_POOL_ZPOOL_CHECKPOINT) is populated with the uberblock that * references the state of the pool when we take the checkpoint. The entry * remains populated until we start discarding the checkpoint or we rewind * back to it. * * - Each vdev contains a vdev-wide space map while the pool has a checkpoint, * which persists until the checkpoint is fully discarded. The space map * contains entries that have been freed in the current state of the pool * but we want to keep around in case we decide to rewind to the checkpoint. * [see vdev_checkpoint_sm] * * - Each metaslab's ms_sm space map behaves the same as without the * checkpoint, with the only exception being the scenario when we free * blocks that belong to the checkpoint. In this case, these blocks remain * ALLOCATED in the metaslab's space map and they are added as FREE in the * vdev's checkpoint space map. * * - Each uberblock has a field (ub_checkpoint_txg) which holds the txg that * the uberblock was checkpointed. For normal uberblocks this field is 0. * * == Overview of operations == * * - To create a checkpoint, we first wait for the current TXG to be synced, * so we can use the most recently synced uberblock (spa_ubsync) as the * checkpointed uberblock. Then we use an early synctask to place that * uberblock in MOS config, increment the feature flag for the checkpoint * (marking it active), and setting spa_checkpoint_txg (see its use below) * to the TXG of the checkpointed uberblock. We use an early synctask for * the aforementioned operations to ensure that no blocks were dirtied * between the current TXG and the TXG of the checkpointed uberblock * (e.g the previous txg). * * - When a checkpoint exists, we need to ensure that the blocks that * belong to the checkpoint are freed but never reused. This means that * these blocks should never end up in the ms_allocatable or the ms_freeing * trees of a metaslab. Therefore, whenever there is a checkpoint the new * ms_checkpointing tree is used in addition to the aforementioned ones. * * Whenever a block is freed and we find out that it is referenced by the * checkpoint (we find out by comparing its birth to spa_checkpoint_txg), * we place it in the ms_checkpointing tree instead of the ms_freeingtree. * This way, we divide the blocks that are being freed into checkpointed * and not-checkpointed blocks. * * In order to persist these frees, we write the extents from the * ms_freeingtree to the ms_sm as usual, and the extents from the * ms_checkpointing tree to the vdev_checkpoint_sm. This way, these * checkpointed extents will remain allocated in the metaslab's ms_sm space * map, and therefore won't be reused [see metaslab_sync()]. In addition, * when we discard the checkpoint, we can find the entries that have * actually been freed in vdev_checkpoint_sm. * [see spa_checkpoint_discard_thread_sync()] * * - To discard the checkpoint we use an early synctask to delete the * checkpointed uberblock from the MOS config, set spa_checkpoint_txg to 0, * and wakeup the discarding zthr thread (an open-context async thread). * We use an early synctask to ensure that the operation happens before any * new data end up in the checkpoint's data structures. * * Once the synctask is done and the discarding zthr is awake, we discard * the checkpointed data over multiple TXGs by having the zthr prefetching * entries from vdev_checkpoint_sm and then starting a synctask that places * them as free blocks in to their respective ms_allocatable and ms_sm * structures. * [see spa_checkpoint_discard_thread()] * * When there are no entries left in the vdev_checkpoint_sm of all * top-level vdevs, a final synctask runs that decrements the feature flag. * * - To rewind to the checkpoint, we first use the current uberblock and * open the MOS so we can access the checkpointed uberblock from the MOS * config. After we retrieve the checkpointed uberblock, we use it as the * current uberblock for the pool by writing it to disk with an updated * TXG, opening its version of the MOS, and moving on as usual from there. * [see spa_ld_checkpoint_rewind()] * * An important note on rewinding to the checkpoint has to do with how we * handle ZIL blocks. In the scenario of a rewind, we clear out any ZIL * blocks that have not been claimed by the time we took the checkpoint * as they should no longer be valid. * [see comment in zil_claim()] * * == Miscellaneous information == * * - In the hypothetical event that we take a checkpoint, remove a vdev, * and attempt to rewind, the rewind would fail as the checkpointed * uberblock would reference data in the removed device. For this reason * and others of similar nature, we disallow the following operations that * can change the config: * vdev removal and attach/detach, mirror splitting, and pool reguid. * * - As most of the checkpoint logic is implemented in the SPA and doesn't * distinguish datasets when it comes to space accounting, having a * checkpoint can potentially break the boundaries set by dataset * reservations. */ #include <sys/dmu_tx.h> #include <sys/dsl_dir.h> #include <sys/dsl_synctask.h> #include <sys/metaslab_impl.h> #include <sys/spa.h> #include <sys/spa_impl.h> #include <sys/spa_checkpoint.h> #include <sys/vdev_impl.h> #include <sys/zap.h> #include <sys/zfeature.h> /* * The following parameter limits the amount of memory to be used for the * prefetching of the checkpoint space map done on each vdev while * discarding the checkpoint. * * The reason it exists is because top-level vdevs with long checkpoint * space maps can potentially take up a lot of memory depending on the * amount of checkpointed data that has been freed within them while * the pool had a checkpoint. */ uint64_t zfs_spa_discard_memory_limit = 16 * 1024 * 1024; int spa_checkpoint_get_stats(spa_t *spa, pool_checkpoint_stat_t *pcs) { if (!spa_feature_is_active(spa, SPA_FEATURE_POOL_CHECKPOINT)) return (SET_ERROR(ZFS_ERR_NO_CHECKPOINT)); bzero(pcs, sizeof (pool_checkpoint_stat_t)); int error = zap_contains(spa_meta_objset(spa), DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_ZPOOL_CHECKPOINT); ASSERT(error == 0 || error == ENOENT); if (error == ENOENT) pcs->pcs_state = CS_CHECKPOINT_DISCARDING; else pcs->pcs_state = CS_CHECKPOINT_EXISTS; pcs->pcs_space = spa->spa_checkpoint_info.sci_dspace; pcs->pcs_start_time = spa->spa_checkpoint_info.sci_timestamp; return (0); } static void spa_checkpoint_discard_complete_sync(void *arg, dmu_tx_t *tx) { spa_t *spa = arg; spa->spa_checkpoint_info.sci_timestamp = 0; spa_feature_decr(spa, SPA_FEATURE_POOL_CHECKPOINT, tx); spa_history_log_internal(spa, "spa discard checkpoint", tx, "finished discarding checkpointed state from the pool"); } typedef struct spa_checkpoint_discard_sync_callback_arg { vdev_t *sdc_vd; uint64_t sdc_txg; uint64_t sdc_entry_limit; } spa_checkpoint_discard_sync_callback_arg_t; static int spa_checkpoint_discard_sync_callback(space_map_entry_t *sme, void *arg) { spa_checkpoint_discard_sync_callback_arg_t *sdc = arg; vdev_t *vd = sdc->sdc_vd; metaslab_t *ms = vd->vdev_ms[sme->sme_offset >> vd->vdev_ms_shift]; uint64_t end = sme->sme_offset + sme->sme_run; if (sdc->sdc_entry_limit == 0) return (EINTR); /* * Since the space map is not condensed, we know that * none of its entries is crossing the boundaries of * its respective metaslab. * * That said, there is no fundamental requirement that * the checkpoint's space map entries should not cross * metaslab boundaries. So if needed we could add code * that handles metaslab-crossing segments in the future. */ VERIFY3U(sme->sme_type, ==, SM_FREE); VERIFY3U(sme->sme_offset, >=, ms->ms_start); VERIFY3U(end, <=, ms->ms_start + ms->ms_size); /* * At this point we should not be processing any * other frees concurrently, so the lock is technically * unnecessary. We use the lock anyway though to * potentially save ourselves from future headaches. */ mutex_enter(&ms->ms_lock); if (range_tree_is_empty(ms->ms_freeing)) vdev_dirty(vd, VDD_METASLAB, ms, sdc->sdc_txg); range_tree_add(ms->ms_freeing, sme->sme_offset, sme->sme_run); mutex_exit(&ms->ms_lock); ASSERT3U(vd->vdev_spa->spa_checkpoint_info.sci_dspace, >=, sme->sme_run); ASSERT3U(vd->vdev_stat.vs_checkpoint_space, >=, sme->sme_run); vd->vdev_spa->spa_checkpoint_info.sci_dspace -= sme->sme_run; vd->vdev_stat.vs_checkpoint_space -= sme->sme_run; sdc->sdc_entry_limit--; return (0); } static void spa_checkpoint_accounting_verify(spa_t *spa) { vdev_t *rvd = spa->spa_root_vdev; uint64_t ckpoint_sm_space_sum = 0; uint64_t vs_ckpoint_space_sum = 0; for (uint64_t c = 0; c < rvd->vdev_children; c++) { vdev_t *vd = rvd->vdev_child[c]; if (vd->vdev_checkpoint_sm != NULL) { ckpoint_sm_space_sum += -space_map_allocated(vd->vdev_checkpoint_sm); vs_ckpoint_space_sum += vd->vdev_stat.vs_checkpoint_space; ASSERT3U(ckpoint_sm_space_sum, ==, vs_ckpoint_space_sum); } else { ASSERT0(vd->vdev_stat.vs_checkpoint_space); } } ASSERT3U(spa->spa_checkpoint_info.sci_dspace, ==, ckpoint_sm_space_sum); } static void spa_checkpoint_discard_thread_sync(void *arg, dmu_tx_t *tx) { vdev_t *vd = arg; int error; /* * The space map callback is applied only to non-debug entries. * Because the number of debug entries is less or equal to the * number of non-debug entries, we want to ensure that we only * read what we prefetched from open-context. * * Thus, we set the maximum entries that the space map callback * will be applied to be half the entries that could fit in the * imposed memory limit. * * Note that since this is a conservative estimate we also * assume the worst case scenario in our computation where each * entry is two-word. */ uint64_t max_entry_limit = (zfs_spa_discard_memory_limit / (2 * sizeof (uint64_t))) >> 1; /* * Iterate from the end of the space map towards the beginning, * placing its entries on ms_freeing and removing them from the * space map. The iteration stops if one of the following * conditions is true: * * 1] We reached the beginning of the space map. At this point * the space map should be completely empty and * space_map_incremental_destroy should have returned 0. * The next step would be to free and close the space map * and remove its entry from its vdev's top zap. This allows * spa_checkpoint_discard_thread() to move on to the next vdev. * * 2] We reached the memory limit (amount of memory used to hold * space map entries in memory) and space_map_incremental_destroy * returned EINTR. This means that there are entries remaining * in the space map that will be cleared in a future invocation * of this function by spa_checkpoint_discard_thread(). */ spa_checkpoint_discard_sync_callback_arg_t sdc; sdc.sdc_vd = vd; sdc.sdc_txg = tx->tx_txg; sdc.sdc_entry_limit = max_entry_limit; uint64_t words_before = space_map_length(vd->vdev_checkpoint_sm) / sizeof (uint64_t); error = space_map_incremental_destroy(vd->vdev_checkpoint_sm, spa_checkpoint_discard_sync_callback, &sdc, tx); uint64_t words_after = space_map_length(vd->vdev_checkpoint_sm) / sizeof (uint64_t); #ifdef DEBUG spa_checkpoint_accounting_verify(vd->vdev_spa); #endif zfs_dbgmsg("discarding checkpoint: txg %llu, vdev id %d, " "deleted %llu words - %llu words are left", tx->tx_txg, vd->vdev_id, (words_before - words_after), words_after); if (error != EINTR) { if (error != 0) { zfs_panic_recover("zfs: error %d was returned " "while incrementally destroying the checkpoint " "space map of vdev %llu\n", error, vd->vdev_id); } ASSERT0(words_after); ASSERT0(space_map_allocated(vd->vdev_checkpoint_sm)); ASSERT0(space_map_length(vd->vdev_checkpoint_sm)); space_map_free(vd->vdev_checkpoint_sm, tx); space_map_close(vd->vdev_checkpoint_sm); vd->vdev_checkpoint_sm = NULL; VERIFY0(zap_remove(spa_meta_objset(vd->vdev_spa), vd->vdev_top_zap, VDEV_TOP_ZAP_POOL_CHECKPOINT_SM, tx)); } } static boolean_t spa_checkpoint_discard_is_done(spa_t *spa) { vdev_t *rvd = spa->spa_root_vdev; ASSERT(!spa_has_checkpoint(spa)); ASSERT(spa_feature_is_active(spa, SPA_FEATURE_POOL_CHECKPOINT)); for (uint64_t c = 0; c < rvd->vdev_children; c++) { if (rvd->vdev_child[c]->vdev_checkpoint_sm != NULL) return (B_FALSE); ASSERT0(rvd->vdev_child[c]->vdev_stat.vs_checkpoint_space); } return (B_TRUE); } /* ARGSUSED */ boolean_t spa_checkpoint_discard_thread_check(void *arg, zthr_t *zthr) { spa_t *spa = arg; if (!spa_feature_is_active(spa, SPA_FEATURE_POOL_CHECKPOINT)) return (B_FALSE); if (spa_has_checkpoint(spa)) return (B_FALSE); return (B_TRUE); } void spa_checkpoint_discard_thread(void *arg, zthr_t *zthr) { spa_t *spa = arg; vdev_t *rvd = spa->spa_root_vdev; for (uint64_t c = 0; c < rvd->vdev_children; c++) { vdev_t *vd = rvd->vdev_child[c]; while (vd->vdev_checkpoint_sm != NULL) { space_map_t *checkpoint_sm = vd->vdev_checkpoint_sm; int numbufs; dmu_buf_t **dbp; if (zthr_iscancelled(zthr)) return; ASSERT3P(vd->vdev_ops, !=, &vdev_indirect_ops); uint64_t size = MIN(space_map_length(checkpoint_sm), zfs_spa_discard_memory_limit); uint64_t offset = space_map_length(checkpoint_sm) - size; /* * Ensure that the part of the space map that will * be destroyed by the synctask, is prefetched in * memory before the synctask runs. */ int error = dmu_buf_hold_array_by_bonus( checkpoint_sm->sm_dbuf, offset, size, B_TRUE, FTAG, &numbufs, &dbp); if (error != 0) { zfs_panic_recover("zfs: error %d was returned " "while prefetching checkpoint space map " "entries of vdev %llu\n", error, vd->vdev_id); } VERIFY0(dsl_sync_task(spa->spa_name, NULL, spa_checkpoint_discard_thread_sync, vd, 0, ZFS_SPACE_CHECK_NONE)); dmu_buf_rele_array(dbp, numbufs, FTAG); } } VERIFY(spa_checkpoint_discard_is_done(spa)); VERIFY0(spa->spa_checkpoint_info.sci_dspace); VERIFY0(dsl_sync_task(spa->spa_name, NULL, spa_checkpoint_discard_complete_sync, spa, 0, ZFS_SPACE_CHECK_NONE)); } /* ARGSUSED */ static int spa_checkpoint_check(void *arg, dmu_tx_t *tx) { spa_t *spa = dmu_tx_pool(tx)->dp_spa; if (!spa_feature_is_enabled(spa, SPA_FEATURE_POOL_CHECKPOINT)) return (SET_ERROR(ENOTSUP)); if (!spa_top_vdevs_spacemap_addressable(spa)) return (SET_ERROR(ZFS_ERR_VDEV_TOO_BIG)); if (spa->spa_vdev_removal != NULL) return (SET_ERROR(ZFS_ERR_DEVRM_IN_PROGRESS)); if (spa->spa_checkpoint_txg != 0) return (SET_ERROR(ZFS_ERR_CHECKPOINT_EXISTS)); if (spa_feature_is_active(spa, SPA_FEATURE_POOL_CHECKPOINT)) return (SET_ERROR(ZFS_ERR_DISCARDING_CHECKPOINT)); return (0); } /* ARGSUSED */ static void spa_checkpoint_sync(void *arg, dmu_tx_t *tx) { dsl_pool_t *dp = dmu_tx_pool(tx); spa_t *spa = dp->dp_spa; uberblock_t checkpoint = spa->spa_ubsync; /* * At this point, there should not be a checkpoint in the MOS. */ ASSERT3U(zap_contains(spa_meta_objset(spa), DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_ZPOOL_CHECKPOINT), ==, ENOENT); ASSERT0(spa->spa_checkpoint_info.sci_timestamp); ASSERT0(spa->spa_checkpoint_info.sci_dspace); /* * Since the checkpointed uberblock is the one that just got synced * (we use spa_ubsync), its txg must be equal to the txg number of * the txg we are syncing, minus 1. */ ASSERT3U(checkpoint.ub_txg, ==, spa->spa_syncing_txg - 1); /* * Once the checkpoint is in place, we need to ensure that none of * its blocks will be marked for reuse after it has been freed. * When there is a checkpoint and a block is freed, we compare its * birth txg to the txg of the checkpointed uberblock to see if the * block is part of the checkpoint or not. Therefore, we have to set * spa_checkpoint_txg before any frees happen in this txg (which is * why this is done as an early_synctask as explained in the comment * in spa_checkpoint()). */ spa->spa_checkpoint_txg = checkpoint.ub_txg; spa->spa_checkpoint_info.sci_timestamp = checkpoint.ub_timestamp; checkpoint.ub_checkpoint_txg = checkpoint.ub_txg; VERIFY0(zap_add(spa->spa_dsl_pool->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_ZPOOL_CHECKPOINT, sizeof (uint64_t), sizeof (uberblock_t) / sizeof (uint64_t), &checkpoint, tx)); /* * Increment the feature refcount and thus activate the feature. * Note that the feature will be deactivated when we've * completely discarded all checkpointed state (both vdev * space maps and uberblock). */ spa_feature_incr(spa, SPA_FEATURE_POOL_CHECKPOINT, tx); spa_history_log_internal(spa, "spa checkpoint", tx, "checkpointed uberblock txg=%llu", checkpoint.ub_txg); } /* * Create a checkpoint for the pool. */ int spa_checkpoint(const char *pool) { int error; spa_t *spa; error = spa_open(pool, &spa, FTAG); if (error != 0) return (error); mutex_enter(&spa->spa_vdev_top_lock); /* * Wait for current syncing txg to finish so the latest synced * uberblock (spa_ubsync) has all the changes that we expect * to see if we were to revert later to the checkpoint. In other * words we want the checkpointed uberblock to include/reference * all the changes that were pending at the time that we issued * the checkpoint command. */ txg_wait_synced(spa_get_dsl(spa), 0); /* * As the checkpointed uberblock references blocks from the previous * txg (spa_ubsync) we want to ensure that are not freeing any of * these blocks in the same txg that the following synctask will * run. Thus, we run it as an early synctask, so the dirty changes * that are synced to disk afterwards during zios and other synctasks * do not reuse checkpointed blocks. */ error = dsl_early_sync_task(pool, spa_checkpoint_check, spa_checkpoint_sync, NULL, 0, ZFS_SPACE_CHECK_NORMAL); mutex_exit(&spa->spa_vdev_top_lock); spa_close(spa, FTAG); return (error); } /* ARGSUSED */ static int spa_checkpoint_discard_check(void *arg, dmu_tx_t *tx) { spa_t *spa = dmu_tx_pool(tx)->dp_spa; if (!spa_feature_is_active(spa, SPA_FEATURE_POOL_CHECKPOINT)) return (SET_ERROR(ZFS_ERR_NO_CHECKPOINT)); if (spa->spa_checkpoint_txg == 0) return (SET_ERROR(ZFS_ERR_DISCARDING_CHECKPOINT)); VERIFY0(zap_contains(spa_meta_objset(spa), DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_ZPOOL_CHECKPOINT)); return (0); } /* ARGSUSED */ static void spa_checkpoint_discard_sync(void *arg, dmu_tx_t *tx) { spa_t *spa = dmu_tx_pool(tx)->dp_spa; VERIFY0(zap_remove(spa_meta_objset(spa), DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_ZPOOL_CHECKPOINT, tx)); spa->spa_checkpoint_txg = 0; zthr_wakeup(spa->spa_checkpoint_discard_zthr); spa_history_log_internal(spa, "spa discard checkpoint", tx, "started discarding checkpointed state from the pool"); } /* * Discard the checkpoint from a pool. */ int spa_checkpoint_discard(const char *pool) { /* * Similarly to spa_checkpoint(), we want our synctask to run * before any pending dirty data are written to disk so they * won't end up in the checkpoint's data structures (e.g. * ms_checkpointing and vdev_checkpoint_sm) and re-create any * space maps that the discarding open-context thread has * deleted. * [see spa_discard_checkpoint_sync and spa_discard_checkpoint_thread] */ return (dsl_early_sync_task(pool, spa_checkpoint_discard_check, spa_checkpoint_discard_sync, NULL, 0, ZFS_SPACE_CHECK_DISCARD_CHECKPOINT)); }
