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Optimize allocation throttling

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Remove mc_lock use from metaslab_class_throttle_*().  The math there
is based on refcounts and so atomic, so the only race possible there
is between zfs_refcount_count() and zfs_refcount_add().  But in most
cases metaslab_class_throttle_reserve() is called with the allocator
lock held, which covers the race.  In cases where the lock is not
held, GANG_ALLOCATION() or METASLAB_MUST_RESERVE are set, and so we
do not use zfs_refcount_count().  And even if we assume some other
non-existing scenario, the worst that may happen from this race is
few more I/Os get to allocation earlier, that is not a problem.

Move locks and data of different allocators into different cache
lines to avoid false sharing.  Group spa_alloc_* arrays together
into single array of aligned struct spa_alloc spa_allocs.  Align
struct metaslab_class_allocator.

Reviewed-by: Paul Dagnelie <pcd@delphix.com>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Don Brady <don.brady@delphix.com>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored-By: iXsystems, Inc.
Closes #12314
This commit is contained in:
Alexander Motin
2021-07-21 08:40:36 -04:00
committed by GitHub
parent bc93935ef0
commit 1b50749ce9
6 changed files with 45 additions and 58 deletions
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module/zfs/spa.c
+6 -6
View File
@@ -9197,9 +9197,9 @@ spa_sync(spa_t *spa, uint64_t txg)
spa->spa_sync_pass = 0;
for (int i = 0; i < spa->spa_alloc_count; i++) {
mutex_enter(&spa->spa_alloc_locks[i]);
VERIFY0(avl_numnodes(&spa->spa_alloc_trees[i]));
mutex_exit(&spa->spa_alloc_locks[i]);
mutex_enter(&spa->spa_allocs[i].spaa_lock);
VERIFY0(avl_numnodes(&spa->spa_allocs[i].spaa_tree));
mutex_exit(&spa->spa_allocs[i].spaa_lock);
}
/*
@@ -9309,9 +9309,9 @@ spa_sync(spa_t *spa, uint64_t txg)
dsl_pool_sync_done(dp, txg);
for (int i = 0; i < spa->spa_alloc_count; i++) {
mutex_enter(&spa->spa_alloc_locks[i]);
VERIFY0(avl_numnodes(&spa->spa_alloc_trees[i]));
mutex_exit(&spa->spa_alloc_locks[i]);
mutex_enter(&spa->spa_allocs[i].spaa_lock);
VERIFY0(avl_numnodes(&spa->spa_allocs[i].spaa_tree));
mutex_exit(&spa->spa_allocs[i].spaa_lock);
}
/*