diff options
Diffstat (limited to 'module/zfs/zil.c')
| -rw-r--r-- | module/zfs/zil.c | 93 |
1 files changed, 44 insertions, 49 deletions
diff --git a/module/zfs/zil.c b/module/zfs/zil.c index 1af357c58..34be54b33 100644 --- a/module/zfs/zil.c +++ b/module/zfs/zil.c @@ -125,10 +125,9 @@ static kstat_t *zil_kstats_global; int zil_replay_disable = 0; /* - * Disable the DKIOCFLUSHWRITECACHE commands that are normally sent to - * the disk(s) by the ZIL after an LWB write has completed. Setting this - * will cause ZIL corruption on power loss if a volatile out-of-order - * write cache is enabled. + * Disable the flush commands that are normally sent to the disk(s) by the ZIL + * after an LWB write has completed. Setting this will cause ZIL corruption on + * power loss if a volatile out-of-order write cache is enabled. */ static int zil_nocacheflush = 0; @@ -1406,19 +1405,17 @@ zil_lwb_add_txg(lwb_t *lwb, uint64_t txg) } /* - * This function is a called after all vdevs associated with a given lwb - * write have completed their DKIOCFLUSHWRITECACHE command; or as soon - * as the lwb write completes, if "zil_nocacheflush" is set. Further, - * all "previous" lwb's will have completed before this function is - * called; i.e. this function is called for all previous lwbs before - * it's called for "this" lwb (enforced via zio the dependencies - * configured in zil_lwb_set_zio_dependency()). + * This function is a called after all vdevs associated with a given lwb write + * have completed their flush command; or as soon as the lwb write completes, + * if "zil_nocacheflush" is set. Further, all "previous" lwb's will have + * completed before this function is called; i.e. this function is called for + * all previous lwbs before it's called for "this" lwb (enforced via zio the + * dependencies configured in zil_lwb_set_zio_dependency()). * - * The intention is for this function to be called as soon as the - * contents of an lwb are considered "stable" on disk, and will survive - * any sudden loss of power. At this point, any threads waiting for the - * lwb to reach this state are signalled, and the "waiter" structures - * are marked "done". + * The intention is for this function to be called as soon as the contents of + * an lwb are considered "stable" on disk, and will survive any sudden loss of + * power. At this point, any threads waiting for the lwb to reach this state + * are signalled, and the "waiter" structures are marked "done". */ static void zil_lwb_flush_vdevs_done(zio_t *zio) @@ -1532,17 +1529,16 @@ zil_lwb_flush_wait_all(zilog_t *zilog, uint64_t txg) } /* - * This is called when an lwb's write zio completes. The callback's - * purpose is to issue the DKIOCFLUSHWRITECACHE commands for the vdevs - * in the lwb's lwb_vdev_tree. The tree will contain the vdevs involved - * in writing out this specific lwb's data, and in the case that cache - * flushes have been deferred, vdevs involved in writing the data for - * previous lwbs. The writes corresponding to all the vdevs in the - * lwb_vdev_tree will have completed by the time this is called, due to - * the zio dependencies configured in zil_lwb_set_zio_dependency(), - * which takes deferred flushes into account. The lwb will be "done" - * once zil_lwb_flush_vdevs_done() is called, which occurs in the zio - * completion callback for the lwb's root zio. + * This is called when an lwb's write zio completes. The callback's purpose is + * to issue the flush commands for the vdevs in the lwb's lwb_vdev_tree. The + * tree will contain the vdevs involved in writing out this specific lwb's + * data, and in the case that cache flushes have been deferred, vdevs involved + * in writing the data for previous lwbs. The writes corresponding to all the + * vdevs in the lwb_vdev_tree will have completed by the time this is called, + * due to the zio dependencies configured in zil_lwb_set_zio_dependency(), + * which takes deferred flushes into account. The lwb will be "done" once + * zil_lwb_flush_vdevs_done() is called, which occurs in the zio completion + * callback for the lwb's root zio. */ static void zil_lwb_write_done(zio_t *zio) @@ -1601,19 +1597,18 @@ zil_lwb_write_done(zio_t *zio) } /* - * If this lwb does not have any threads waiting for it to - * complete, we want to defer issuing the DKIOCFLUSHWRITECACHE - * command to the vdevs written to by "this" lwb, and instead - * rely on the "next" lwb to handle the DKIOCFLUSHWRITECACHE - * command for those vdevs. Thus, we merge the vdev tree of - * "this" lwb with the vdev tree of the "next" lwb in the list, - * and assume the "next" lwb will handle flushing the vdevs (or - * deferring the flush(s) again). + * If this lwb does not have any threads waiting for it to complete, we + * want to defer issuing the flush command to the vdevs written to by + * "this" lwb, and instead rely on the "next" lwb to handle the flush + * command for those vdevs. Thus, we merge the vdev tree of "this" lwb + * with the vdev tree of the "next" lwb in the list, and assume the + * "next" lwb will handle flushing the vdevs (or deferring the flush(s) + * again). * - * This is a useful performance optimization, especially for - * workloads with lots of async write activity and few sync - * write and/or fsync activity, as it has the potential to - * coalesce multiple flush commands to a vdev into one. + * This is a useful performance optimization, especially for workloads + * with lots of async write activity and few sync write and/or fsync + * activity, as it has the potential to coalesce multiple flush + * commands to a vdev into one. */ if (list_is_empty(&lwb->lwb_waiters) && nlwb != NULL) { zil_lwb_flush_defer(lwb, nlwb); @@ -1663,16 +1658,16 @@ zil_lwb_set_zio_dependency(zilog_t *zilog, lwb_t *lwb) * If the previous lwb's write hasn't already completed, we also want * to order the completion of the lwb write zios (above, we only order * the completion of the lwb root zios). This is required because of - * how we can defer the DKIOCFLUSHWRITECACHE commands for each lwb. + * how we can defer the flush commands for each lwb. * - * When the DKIOCFLUSHWRITECACHE commands are deferred, the previous - * lwb will rely on this lwb to flush the vdevs written to by that - * previous lwb. Thus, we need to ensure this lwb doesn't issue the - * flush until after the previous lwb's write completes. We ensure - * this ordering by setting the zio parent/child relationship here. + * When the flush commands are deferred, the previous lwb will rely on + * this lwb to flush the vdevs written to by that previous lwb. Thus, + * we need to ensure this lwb doesn't issue the flush until after the + * previous lwb's write completes. We ensure this ordering by setting + * the zio parent/child relationship here. * - * Without this relationship on the lwb's write zio, it's possible - * for this lwb's write to complete prior to the previous lwb's write + * Without this relationship on the lwb's write zio, it's possible for + * this lwb's write to complete prior to the previous lwb's write * completing; and thus, the vdevs for the previous lwb would be * flushed prior to that lwb's data being written to those vdevs (the * vdevs are flushed in the lwb write zio's completion handler, @@ -3499,8 +3494,8 @@ zil_commit_itx_assign(zilog_t *zilog, zil_commit_waiter_t *zcw) * callback of the lwb's zio[*]. * * * Actually, the waiters are signaled in the zio completion - * callback of the root zio for the DKIOCFLUSHWRITECACHE commands - * that are sent to the vdevs upon completion of the lwb zio. + * callback of the root zio for the flush commands that are sent to + * the vdevs upon completion of the lwb zio. * * 2. When the itxs are inserted into the ZIL's queue of uncommitted * itxs, the order in which they are inserted is preserved[*]; as |