X-Git-Url: https://git.camperquake.de/gitweb.cgi?a=blobdiff_plain;f=module%2Fzfs%2Ftxg.c;h=7c820af4f8b3e8f6f6b070c2d2bba6745d015e4d;hb=refs%2Fheads%2Frertzinger%2Ffeature-zpool-get--p;hp=c234567d7e5295f6437f8b417f7b5d3c4c3ce130;hpb=b876dac776afc8ea2c598eac53b9903de01c6172;p=zfs.git diff --git a/module/zfs/txg.c b/module/zfs/txg.c index c234567..7c820af 100644 --- a/module/zfs/txg.c +++ b/module/zfs/txg.c @@ -20,6 +20,8 @@ */ /* * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved. + * Portions Copyright 2011 Martin Matuska + * Copyright (c) 2013 by Delphix. All rights reserved. */ #include @@ -29,9 +31,79 @@ #include #include #include +#include /* - * Pool-wide transaction groups. + * ZFS Transaction Groups + * ---------------------- + * + * ZFS transaction groups are, as the name implies, groups of transactions + * that act on persistent state. ZFS asserts consistency at the granularity of + * these transaction groups. Each successive transaction group (txg) is + * assigned a 64-bit consecutive identifier. There are three active + * transaction group states: open, quiescing, or syncing. At any given time, + * there may be an active txg associated with each state; each active txg may + * either be processing, or blocked waiting to enter the next state. There may + * be up to three active txgs, and there is always a txg in the open state + * (though it may be blocked waiting to enter the quiescing state). In broad + * strokes, transactions — operations that change in-memory structures — are + * accepted into the txg in the open state, and are completed while the txg is + * in the open or quiescing states. The accumulated changes are written to + * disk in the syncing state. + * + * Open + * + * When a new txg becomes active, it first enters the open state. New + * transactions — updates to in-memory structures — are assigned to the + * currently open txg. There is always a txg in the open state so that ZFS can + * accept new changes (though the txg may refuse new changes if it has hit + * some limit). ZFS advances the open txg to the next state for a variety of + * reasons such as it hitting a time or size threshold, or the execution of an + * administrative action that must be completed in the syncing state. + * + * Quiescing + * + * After a txg exits the open state, it enters the quiescing state. The + * quiescing state is intended to provide a buffer between accepting new + * transactions in the open state and writing them out to stable storage in + * the syncing state. While quiescing, transactions can continue their + * operation without delaying either of the other states. Typically, a txg is + * in the quiescing state very briefly since the operations are bounded by + * software latencies rather than, say, slower I/O latencies. After all + * transactions complete, the txg is ready to enter the next state. + * + * Syncing + * + * In the syncing state, the in-memory state built up during the open and (to + * a lesser degree) the quiescing states is written to stable storage. The + * process of writing out modified data can, in turn modify more data. For + * example when we write new blocks, we need to allocate space for them; those + * allocations modify metadata (space maps)... which themselves must be + * written to stable storage. During the sync state, ZFS iterates, writing out + * data until it converges and all in-memory changes have been written out. + * The first such pass is the largest as it encompasses all the modified user + * data (as opposed to filesystem metadata). Subsequent passes typically have + * far less data to write as they consist exclusively of filesystem metadata. + * + * To ensure convergence, after a certain number of passes ZFS begins + * overwriting locations on stable storage that had been allocated earlier in + * the syncing state (and subsequently freed). ZFS usually allocates new + * blocks to optimize for large, continuous, writes. For the syncing state to + * converge however it must complete a pass where no new blocks are allocated + * since each allocation requires a modification of persistent metadata. + * Further, to hasten convergence, after a prescribed number of passes, ZFS + * also defers frees, and stops compressing. + * + * In addition to writing out user data, we must also execute synctasks during + * the syncing context. A synctask is the mechanism by which some + * administrative activities work such as creating and destroying snapshots or + * datasets. Note that when a synctask is initiated it enters the open txg, + * and ZFS then pushes that txg as quickly as possible to completion of the + * syncing state in order to reduce the latency of the administrative + * activity. To complete the syncing state, ZFS writes out a new uberblock, + * the root of the tree of blocks that comprise all state stored on the ZFS + * pool. Finally, if there is a quiesced txg waiting, we signal that it can + * now transition to the syncing state. */ static void txg_sync_thread(dsl_pool_t *dp); @@ -279,6 +351,8 @@ txg_rele_to_sync(txg_handle_t *th) static void txg_quiesce(dsl_pool_t *dp, uint64_t txg) { + hrtime_t start; + txg_history_t *th; tx_state_t *tx = &dp->dp_tx; int g = txg & TXG_MASK; int c; @@ -300,8 +374,19 @@ txg_quiesce(dsl_pool_t *dp, uint64_t txg) mutex_exit(&tx->tx_cpu[c].tc_lock); /* + * Measure how long the txg was open and replace the kstat. + */ + th = dsl_pool_txg_history_get(dp, txg); + th->th_kstat.open_time = gethrtime() - th->th_kstat.birth; + th->th_kstat.state = TXG_STATE_QUIESCING; + dsl_pool_txg_history_put(th); + dsl_pool_txg_history_add(dp, tx->tx_open_txg); + + /* * Quiesce the transaction group by waiting for everyone to txg_exit(). */ + start = gethrtime(); + for (c = 0; c < max_ncpus; c++) { tx_cpu_t *tc = &tx->tx_cpu[c]; mutex_enter(&tc->tc_lock); @@ -309,6 +394,13 @@ txg_quiesce(dsl_pool_t *dp, uint64_t txg) cv_wait(&tc->tc_cv[g], &tc->tc_lock); mutex_exit(&tc->tc_lock); } + + /* + * Measure how long the txg took to quiesce. + */ + th = dsl_pool_txg_history_get(dp, txg); + th->th_kstat.quiesce_time = gethrtime() - start; + dsl_pool_txg_history_put(th); } static void @@ -349,7 +441,7 @@ txg_dispatch_callbacks(dsl_pool_t *dp, uint64_t txg) TASKQ_THREADS_CPU_PCT | TASKQ_PREPOPULATE); } - cb_list = kmem_alloc(sizeof (list_t), KM_SLEEP); + cb_list = kmem_alloc(sizeof (list_t), KM_PUSHPAGE); list_create(cb_list, sizeof (dmu_tx_callback_t), offsetof(dmu_tx_callback_t, dcb_node)); @@ -382,13 +474,26 @@ txg_sync_thread(dsl_pool_t *dp) callb_cpr_t cpr; uint64_t start, delta; +#ifdef _KERNEL + /* + * Annotate this process with a flag that indicates that it is + * unsafe to use KM_SLEEP during memory allocations due to the + * potential for a deadlock. KM_PUSHPAGE should be used instead. + */ + current->flags |= PF_NOFS; +#endif /* _KERNEL */ + txg_thread_enter(tx, &cpr); start = delta = 0; for (;;) { - uint64_t timer, timeout = zfs_txg_timeout * hz; + hrtime_t hrstart; + txg_history_t *th; + uint64_t timer, timeout; uint64_t txg; + timeout = zfs_txg_timeout * hz; + /* * We sync when we're scanning, there's someone waiting * on us, or the quiesce thread has handed off a txg to @@ -430,11 +535,17 @@ txg_sync_thread(dsl_pool_t *dp) tx->tx_syncing_txg = txg; cv_broadcast(&tx->tx_quiesce_more_cv); + th = dsl_pool_txg_history_get(dp, txg); + th->th_kstat.state = TXG_STATE_SYNCING; + vdev_get_stats(spa->spa_root_vdev, &th->th_vs1); + dsl_pool_txg_history_put(th); + dprintf("txg=%llu quiesce_txg=%llu sync_txg=%llu\n", txg, tx->tx_quiesce_txg_waiting, tx->tx_sync_txg_waiting); mutex_exit(&tx->tx_sync_lock); start = ddi_get_lbolt(); + hrstart = gethrtime(); spa_sync(spa, txg); delta = ddi_get_lbolt() - start; @@ -447,6 +558,23 @@ txg_sync_thread(dsl_pool_t *dp) * Dispatch commit callbacks to worker threads. */ txg_dispatch_callbacks(dp, txg); + + /* + * Measure the txg sync time determine the amount of I/O done. + */ + th = dsl_pool_txg_history_get(dp, txg); + vdev_get_stats(spa->spa_root_vdev, &th->th_vs2); + th->th_kstat.sync_time = gethrtime() - hrstart; + th->th_kstat.nread = th->th_vs2.vs_bytes[ZIO_TYPE_READ] - + th->th_vs1.vs_bytes[ZIO_TYPE_READ]; + th->th_kstat.nwritten = th->th_vs2.vs_bytes[ZIO_TYPE_WRITE] - + th->th_vs1.vs_bytes[ZIO_TYPE_WRITE]; + th->th_kstat.reads = th->th_vs2.vs_ops[ZIO_TYPE_READ] - + th->th_vs1.vs_ops[ZIO_TYPE_READ]; + th->th_kstat.writes = th->th_vs2.vs_ops[ZIO_TYPE_WRITE] - + th->th_vs1.vs_ops[ZIO_TYPE_WRITE]; + th->th_kstat.state = TXG_STATE_COMMITTED; + dsl_pool_txg_history_put(th); } } @@ -612,7 +740,7 @@ txg_list_destroy(txg_list_t *tl) mutex_destroy(&tl->tl_lock); } -int +boolean_t txg_list_empty(txg_list_t *tl, uint64_t txg) { return (tl->tl_head[txg & TXG_MASK] == NULL); @@ -764,4 +892,7 @@ EXPORT_SYMBOL(txg_wait_open); EXPORT_SYMBOL(txg_wait_callbacks); EXPORT_SYMBOL(txg_stalled); EXPORT_SYMBOL(txg_sync_waiting); + +module_param(zfs_txg_timeout, int, 0644); +MODULE_PARM_DESC(zfs_txg_timeout, "Max seconds worth of delta per txg"); #endif