From 48d2d409eaec2d4d3bd2f2ce80c636ee2714b06d Mon Sep 17 00:00:00 2001 From: Richard Yao Date: Tue, 28 Jul 2015 10:22:56 -0400 Subject: [PATCH] Remove fastwrite mutex The fast write mutex is intended to protect accounting, but it is redundant because all accounting is performed through atomic operations. It also serializes all metaslab IO behind a mutex, which introduces a theoretical scaling regression that the Illumos developers did not like when we showed this to them. Removing it makes the selection of the metaslab_group lock free as it is on Illumos. The selection is not quite the same without the lock because the loop races with IO completions, but any imbalances caused by this are likely to be corrected by subsequent metaslab group selections. Signed-off-by: Richard Yao --- include/sys/metaslab_impl.h | 1 - module/zfs/metaslab.c | 9 --------- 2 files changed, 10 deletions(-) diff --git a/include/sys/metaslab_impl.h b/include/sys/metaslab_impl.h index 88bda071fa73..27a53b515fbc 100644 --- a/include/sys/metaslab_impl.h +++ b/include/sys/metaslab_impl.h @@ -69,7 +69,6 @@ struct metaslab_class { uint64_t mc_space; /* total space (alloc + free) */ uint64_t mc_dspace; /* total deflated space */ uint64_t mc_histogram[RANGE_TREE_HISTOGRAM_SIZE]; - kmutex_t mc_fastwrite_lock; }; /* diff --git a/module/zfs/metaslab.c b/module/zfs/metaslab.c index b328cbb0a106..f67341516c03 100644 --- a/module/zfs/metaslab.c +++ b/module/zfs/metaslab.c @@ -198,7 +198,6 @@ metaslab_class_create(spa_t *spa, metaslab_ops_t *ops) mc->mc_spa = spa; mc->mc_rotor = NULL; mc->mc_ops = ops; - mutex_init(&mc->mc_fastwrite_lock, NULL, MUTEX_DEFAULT, NULL); return (mc); } @@ -212,7 +211,6 @@ metaslab_class_destroy(metaslab_class_t *mc) ASSERT(mc->mc_space == 0); ASSERT(mc->mc_dspace == 0); - mutex_destroy(&mc->mc_fastwrite_lock); kmem_free(mc, sizeof (metaslab_class_t)); } @@ -2213,9 +2211,6 @@ metaslab_alloc_dva(spa_t *spa, metaslab_class_t *mc, uint64_t psize, if (psize >= metaslab_gang_bang && (ddi_get_lbolt() & 3) == 0) return (SET_ERROR(ENOSPC)); - if (flags & METASLAB_FASTWRITE) - mutex_enter(&mc->mc_fastwrite_lock); - /* * Start at the rotor and loop through all mgs until we find something. * Note that there's no locking on mc_rotor or mc_aliquot because @@ -2400,7 +2395,6 @@ metaslab_alloc_dva(spa_t *spa, metaslab_class_t *mc, uint64_t psize, if (flags & METASLAB_FASTWRITE) { atomic_add_64(&vd->vdev_pending_fastwrite, psize); - mutex_exit(&mc->mc_fastwrite_lock); } return (0); @@ -2424,9 +2418,6 @@ metaslab_alloc_dva(spa_t *spa, metaslab_class_t *mc, uint64_t psize, bzero(&dva[d], sizeof (dva_t)); - if (flags & METASLAB_FASTWRITE) - mutex_exit(&mc->mc_fastwrite_lock); - return (SET_ERROR(ENOSPC)); }