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Few microoptimizations to dbuf layer

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Move db_link into the same cache line as db_blkid and db_level.
It allows significantly reduce avl_add() time in dbuf_create() on
systems with large RAM and huge number of dbufs per dnode.

Avoid few accesses to dbuf_caches[].size, which is highly congested
under high IOPS and never stays in cache for a long time.  Use local
value we are receiving from zfs_refcount_add_many() any way.

Remove cache_size_bytes_max bump from dbuf_evict_one().  I don't see
a point to do it on dbuf eviction after we done it on insertion in
dbuf_rele_and_unlock().

Reviewed-by: Matt Ahrens <matt@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored-By: iXsystems, Inc.
Closes #9931
This commit is contained in:
Alexander Motin 2020-02-05 14:08:44 -05:00 committed by GitHub
parent cccbed9f98
commit cbd8f5b759
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GPG Key ID: 4AEE18F83AFDEB23
2 changed files with 16 additions and 28 deletions
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13
include/sys/dbuf.h
View File

@ -206,6 +206,13 @@ typedef struct dmu_buf_impl {
*/
struct dmu_buf_impl *db_hash_next;
/*
* Our link on the owner dnodes's dn_dbufs list.
* Protected by its dn_dbufs_mtx. Should be on the same cache line
* as db_level and db_blkid for the best avl_add() performance.
*/
avl_node_t db_link;
/* our block number */
uint64_t db_blkid;
@ -260,12 +267,6 @@ typedef struct dmu_buf_impl {
/* List of dirty records for the buffer sorted newest to oldest. */
list_t db_dirty_records;
/*
* Our link on the owner dnodes's dn_dbufs list.
* Protected by its dn_dbufs_mtx.
*/
avl_node_t db_link;
/* Link in dbuf_cache or dbuf_metadata_cache */
multilist_node_t db_cache_link;

31
module/zfs/dbuf.c
View File

@ -627,13 +627,6 @@ dbuf_cache_lowater_bytes(void)
(dbuf_cache_target * dbuf_cache_lowater_pct) / 100);
}
static inline boolean_t
dbuf_cache_above_hiwater(void)
{
return (zfs_refcount_count(&dbuf_caches[DB_DBUF_CACHE].size) >
dbuf_cache_hiwater_bytes());
}
static inline boolean_t
dbuf_cache_above_lowater(void)
{
@ -673,8 +666,6 @@ dbuf_evict_one(void)
ASSERT3U(db->db_caching_status, ==, DB_DBUF_CACHE);
db->db_caching_status = DB_NO_CACHE;
dbuf_destroy(db);
DBUF_STAT_MAX(cache_size_bytes_max,
zfs_refcount_count(&dbuf_caches[DB_DBUF_CACHE].size));
DBUF_STAT_BUMP(cache_total_evicts);
} else {
multilist_sublist_unlock(mls);
@ -730,16 +721,15 @@ dbuf_evict_thread(void *unused)
* dbuf cache using the callers context.
*/
static void
dbuf_evict_notify(void)
dbuf_evict_notify(uint64_t size)
{
/*
* We check if we should evict without holding the dbuf_evict_lock,
* because it's OK to occasionally make the wrong decision here,
* and grabbing the lock results in massive lock contention.
*/
if (zfs_refcount_count(&dbuf_caches[DB_DBUF_CACHE].size) >
dbuf_cache_target_bytes()) {
if (dbuf_cache_above_hiwater())
if (size > dbuf_cache_target_bytes()) {
if (size > dbuf_cache_hiwater_bytes())
dbuf_evict_one();
cv_signal(&dbuf_evict_cv);
}
@ -3471,6 +3461,7 @@ void
dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag, boolean_t evicting)
{
int64_t holds;
uint64_t size;
ASSERT(MUTEX_HELD(&db->db_mtx));
DBUF_VERIFY(db);
@ -3567,7 +3558,7 @@ dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag, boolean_t evicting)
db->db_caching_status = dcs;
multilist_insert(dbuf_caches[dcs].cache, db);
(void) zfs_refcount_add_many(
size = zfs_refcount_add_many(
&dbuf_caches[dcs].size,
db->db.db_size, db);
@ -3575,8 +3566,7 @@ dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag, boolean_t evicting)
DBUF_STAT_BUMP(metadata_cache_count);
DBUF_STAT_MAX(
metadata_cache_size_bytes_max,
zfs_refcount_count(
&dbuf_caches[dcs].size));
size);
} else {
DBUF_STAT_BUMP(
cache_levels[db->db_level]);
@ -3585,15 +3575,12 @@ dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag, boolean_t evicting)
cache_levels_bytes[db->db_level],
db->db.db_size);
DBUF_STAT_MAX(cache_size_bytes_max,
zfs_refcount_count(
&dbuf_caches[dcs].size));
size);
}
mutex_exit(&db->db_mtx);
if (db->db_caching_status == DB_DBUF_CACHE &&
!evicting) {
dbuf_evict_notify();
}
if (dcs == DB_DBUF_CACHE && !evicting)
dbuf_evict_notify(size);
}
if (do_arc_evict)