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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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include/sys/metaslab_impl.h
+1 -1
View File
@@ -157,7 +157,7 @@ typedef struct metaslab_class_allocator {
*/
uint64_t mca_alloc_max_slots;
zfs_refcount_t mca_alloc_slots;
} metaslab_class_allocator_t;
} ____cacheline_aligned metaslab_class_allocator_t;
/*
* A metaslab class encompasses a category of allocatable top-level vdevs.
include/sys/spa_impl.h
+9 -6
View File
@@ -57,6 +57,11 @@
extern "C" {
#endif
typedef struct spa_alloc {
kmutex_t spaa_lock;
avl_tree_t spaa_tree;
} ____cacheline_aligned spa_alloc_t;
typedef struct spa_error_entry {
zbookmark_phys_t se_bookmark;
char *se_name;
@@ -250,13 +255,11 @@ struct spa {
list_t spa_config_dirty_list; /* vdevs with dirty config */
list_t spa_state_dirty_list; /* vdevs with dirty state */
/*
* spa_alloc_locks and spa_alloc_trees are arrays, whose lengths are
* stored in spa_alloc_count. There is one tree and one lock for each
* allocator, to help improve allocation performance in write-heavy
* workloads.
* spa_allocs is an array, whose lengths is stored in spa_alloc_count.
* There is one tree and one lock for each allocator, to help improve
* allocation performance in write-heavy workloads.
*/
kmutex_t *spa_alloc_locks;
avl_tree_t *spa_alloc_trees;
spa_alloc_t *spa_allocs;
int spa_alloc_count;
spa_aux_vdev_t spa_spares; /* hot spares */