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Implement parallel dbuf eviction #16487

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Implement parallel dbuf eviction #16487

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96 changes: 65 additions & 31 deletions module/zfs/dbuf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -771,43 +771,77 @@ dbuf_cache_above_lowater(void)
* Evict the oldest eligible dbuf from the dbuf cache.
*/
static void
dbuf_evict_one(void)
dbuf_evict_many(uint64_t bytes)
{
uint64_t evicted = 0;
uint_t num_sublists = multilist_get_num_sublists(
&dbuf_caches[DB_DBUF_CACHE].cache);

int idx = multilist_get_random_index(&dbuf_caches[DB_DBUF_CACHE].cache);
multilist_sublist_t *mls = multilist_sublist_lock_idx(
&dbuf_caches[DB_DBUF_CACHE].cache, idx);
int start = idx;

ASSERT(!MUTEX_HELD(&dbuf_evict_lock));
while (evicted < bytes && !dbuf_evict_thread_exit) {
multilist_sublist_t *mls = multilist_sublist_lock_idx(
&dbuf_caches[DB_DBUF_CACHE].cache, idx++);

dmu_buf_impl_t *db = multilist_sublist_tail(mls);
while (db != NULL && mutex_tryenter(&db->db_mtx) == 0) {
db = multilist_sublist_prev(mls, db);
}
ASSERT(!MUTEX_HELD(&dbuf_evict_lock));

DTRACE_PROBE2(dbuf__evict__one, dmu_buf_impl_t *, db,
multilist_sublist_t *, mls);
dmu_buf_impl_t *db = multilist_sublist_tail(mls);
while (db != NULL && mutex_tryenter(&db->db_mtx) == 0) {
db = multilist_sublist_prev(mls, db);
}

if (db != NULL) {
multilist_sublist_remove(mls, db);
multilist_sublist_unlock(mls);
uint64_t size = db->db.db_size;
uint64_t usize = dmu_buf_user_size(&db->db);
(void) zfs_refcount_remove_many(
&dbuf_caches[DB_DBUF_CACHE].size, size, db);
(void) zfs_refcount_remove_many(
&dbuf_caches[DB_DBUF_CACHE].size, usize, db->db_user);
DBUF_STAT_BUMPDOWN(cache_levels[db->db_level]);
DBUF_STAT_BUMPDOWN(cache_count);
DBUF_STAT_DECR(cache_levels_bytes[db->db_level], size + usize);
ASSERT3U(db->db_caching_status, ==, DB_DBUF_CACHE);
db->db_caching_status = DB_NO_CACHE;
dbuf_destroy(db);
DBUF_STAT_BUMP(cache_total_evicts);
} else {
multilist_sublist_unlock(mls);
if (db != NULL) {
multilist_sublist_remove(mls, db);
multilist_sublist_unlock(mls);

DTRACE_PROBE2(dbuf__evict__one, dmu_buf_impl_t *, db,
multilist_sublist_t *, mls);

uint64_t size = db->db.db_size;
uint64_t usize = dmu_buf_user_size(&db->db);

(void) zfs_refcount_remove_many(
&dbuf_caches[DB_DBUF_CACHE].size, size, db);
(void) zfs_refcount_remove_many(
&dbuf_caches[DB_DBUF_CACHE].size, usize,
db->db_user);

DBUF_STAT_BUMPDOWN(cache_levels[db->db_level]);
DBUF_STAT_BUMPDOWN(cache_count);
DBUF_STAT_DECR(cache_levels_bytes[db->db_level],
size + usize);

ASSERT3U(db->db_caching_status, ==, DB_DBUF_CACHE);

db->db_caching_status = DB_NO_CACHE;
dbuf_destroy(db);

DBUF_STAT_BUMP(cache_total_evicts);
} else {
multilist_sublist_unlock(mls);
}

if (idx == start)
break;

if (idx == num_sublists) /* wrap */
idx = 0;
}
}

static void
dbuf_evict(void)
{
int64_t bytes = (zfs_refcount_count(&dbuf_caches[DB_DBUF_CACHE].size) -
dbuf_cache_lowater_bytes());
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Here you are making every thread to evict everything extra. At best you might end up evicting all the cache.


if (bytes <= 0)
return;

dbuf_evict_many(bytes);
}

/*
* The dbuf evict thread is responsible for aging out dbufs from the
* cache. Once the cache has reached it's maximum size, dbufs are removed
Expand Down Expand Up @@ -839,7 +873,7 @@ dbuf_evict_thread(void *unused)
* minimize lock contention.
*/
while (dbuf_cache_above_lowater() && !dbuf_evict_thread_exit) {
dbuf_evict_one();
dbuf_evict();
}

mutex_enter(&dbuf_evict_lock);
Expand All @@ -866,7 +900,7 @@ dbuf_evict_notify(uint64_t size)
*/
if (size > dbuf_cache_target_bytes()) {
if (size > dbuf_cache_hiwater_bytes())
dbuf_evict_one();
dbuf_evict();
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cv_signal(&dbuf_evict_cv);
}
}
Expand Down Expand Up @@ -4106,7 +4140,7 @@ dmu_buf_rele(dmu_buf_t *db, const void *tag)
* dbuf_rele()-->dbuf_rele_and_unlock()-->dbuf_evict_notify()
* ^ |
* | |
* +-----dbuf_destroy()<--dbuf_evict_one()<--------+
* +-----dbuf_destroy()<--dbuf_evict()<--------+
*
*/
void
Expand Down
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