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OpenZFS 9577 - remove zfs_dbuf_evict_key tsd

The zfs_dbuf_evict_key TSD (thread-specific data) is not necessary -
we can instead pass a flag down in a few places to prevent recursive
dbuf eviction. Making this change has 3 benefits:

1. The code semantics are easier to understand.
2. On Linux, performance is improved, because creating/removing
   TSD values (by setting to NULL vs non-NULL) is expensive, and
   we do it very often.
3. According to Nexenta, the current semantics can cause a
   deadlock when concurrently calling dmu_objset_evict_dbufs()
   (which is rare today, but they are working on a "parallel
   unmount" change that triggers this more easily):

Porting Notes:
* Minor conflict with OpenZFS 9337 which has not yet been ported.

Authored by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Serapheim Dimitropoulos <serapheim.dimitro@delphix.com>
Reviewed by: Brad Lewis <brad.lewis@delphix.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>

OpenZFS-issue: https://illumos.org/issues/9577
OpenZFS-commit: openzfs/openzfs#645
External-issue: DLPX-58547
Closes #7602
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ahrens authored and behlendorf committed May 31, 2018
1 parent 232dd8b commit 1fac63e56f370f675b23687ee2e634744c54e818
Showing with 46 additions and 55 deletions.
  1. +2 −2 include/sys/dbuf.h
  2. +2 −2 include/sys/dnode.h
  3. +23 −46 module/zfs/dbuf.c
  4. +4 −3 module/zfs/dnode.c
  5. +15 −2 module/zfs/dnode_sync.c
@@ -20,7 +20,7 @@
*/
/*
* Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2012, 2015 by Delphix. All rights reserved.
* Copyright (c) 2012, 2018 by Delphix. All rights reserved.
* Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
* Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
*/
@@ -305,7 +305,7 @@ boolean_t dbuf_try_add_ref(dmu_buf_t *db, objset_t *os, uint64_t obj,
uint64_t dbuf_refcount(dmu_buf_impl_t *db);

void dbuf_rele(dmu_buf_impl_t *db, void *tag);
void dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag);
void dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag, boolean_t evicting);

dmu_buf_impl_t *dbuf_find(struct objset *os, uint64_t object, uint8_t level,
uint64_t blkid);
@@ -20,7 +20,7 @@
*/
/*
* Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2012, 2017 by Delphix. All rights reserved.
* Copyright (c) 2012, 2018 by Delphix. All rights reserved.
* Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
*/

@@ -408,7 +408,7 @@ int dnode_hold_impl(struct objset *dd, uint64_t object, int flag, int dn_slots,
void *ref, dnode_t **dnp);
boolean_t dnode_add_ref(dnode_t *dn, void *ref);
void dnode_rele(dnode_t *dn, void *ref);
void dnode_rele_and_unlock(dnode_t *dn, void *tag);
void dnode_rele_and_unlock(dnode_t *dn, void *tag, boolean_t evicting);
void dnode_setdirty(dnode_t *dn, dmu_tx_t *tx);
void dnode_sync(dnode_t *dn, dmu_tx_t *tx);
void dnode_allocate(dnode_t *dn, dmu_object_type_t ot, int blocksize, int ibs,
@@ -155,8 +155,6 @@ static void __dbuf_hold_impl_init(struct dbuf_hold_impl_data *dh,
void *tag, dmu_buf_impl_t **dbp, int depth);
static int __dbuf_hold_impl(struct dbuf_hold_impl_data *dh);

uint_t zfs_dbuf_evict_key;

static boolean_t dbuf_undirty(dmu_buf_impl_t *db, dmu_tx_t *tx);
static void dbuf_write(dbuf_dirty_record_t *dr, arc_buf_t *data, dmu_tx_t *tx);

@@ -596,14 +594,6 @@ dbuf_evict_one(void)

ASSERT(!MUTEX_HELD(&dbuf_evict_lock));

/*
* Set the thread's tsd to indicate that it's processing evictions.
* Once a thread stops evicting from the dbuf cache it will
* reset its tsd to NULL.
*/
ASSERT3P(tsd_get(zfs_dbuf_evict_key), ==, NULL);
(void) tsd_set(zfs_dbuf_evict_key, (void *)B_TRUE);

dmu_buf_impl_t *db = multilist_sublist_tail(mls);
while (db != NULL && mutex_tryenter(&db->db_mtx) == 0) {
db = multilist_sublist_prev(mls, db);
@@ -628,7 +618,6 @@ dbuf_evict_one(void)
} else {
multilist_sublist_unlock(mls);
}
(void) tsd_set(zfs_dbuf_evict_key, NULL);
}

/*
@@ -682,29 +671,6 @@ dbuf_evict_thread(void *unused)
static void
dbuf_evict_notify(void)
{

/*
* We use thread specific data to track when a thread has
* started processing evictions. This allows us to avoid deeply
* nested stacks that would have a call flow similar to this:
*
* dbuf_rele()-->dbuf_rele_and_unlock()-->dbuf_evict_notify()
* ^ |
* | |
* +-----dbuf_destroy()<--dbuf_evict_one()<--------+
*
* The dbuf_eviction_thread will always have its tsd set until
* that thread exits. All other threads will only set their tsd
* if they are participating in the eviction process. This only
* happens if the eviction thread is unable to process evictions
* fast enough. To keep the dbuf cache size in check, other threads
* can evict from the dbuf cache directly. Those threads will set
* their tsd values so that we ensure that they only evict one dbuf
* from the dbuf cache.
*/
if (tsd_get(zfs_dbuf_evict_key) != NULL)
return;

/*
* We check if we should evict without holding the dbuf_evict_lock,
* because it's OK to occasionally make the wrong decision here,
@@ -801,7 +767,6 @@ dbuf_init(void)
dbuf_cache_multilist_index_func);
refcount_create(&dbuf_cache_size);

tsd_create(&zfs_dbuf_evict_key, NULL);
dbuf_evict_thread_exit = B_FALSE;
mutex_init(&dbuf_evict_lock, NULL, MUTEX_DEFAULT, NULL);
cv_init(&dbuf_evict_cv, NULL, CV_DEFAULT, NULL);
@@ -858,7 +823,6 @@ dbuf_fini(void)
cv_wait(&dbuf_evict_cv, &dbuf_evict_lock);
}
mutex_exit(&dbuf_evict_lock);
tsd_destroy(&zfs_dbuf_evict_key);

mutex_destroy(&dbuf_evict_lock);
cv_destroy(&dbuf_evict_cv);
@@ -1152,7 +1116,7 @@ dbuf_read_done(zio_t *zio, const zbookmark_phys_t *zb, const blkptr_t *bp,
db->db_state = DB_UNCACHED;
}
cv_broadcast(&db->db_changed);
dbuf_rele_and_unlock(db, NULL);
dbuf_rele_and_unlock(db, NULL, B_FALSE);
}

static int
@@ -2441,7 +2405,8 @@ dbuf_destroy(dmu_buf_impl_t *db)
* value in dnode_move(), since DB_DNODE_EXIT doesn't actually
* release any lock.
*/
dnode_rele(dn, db);
mutex_enter(&dn->dn_mtx);
dnode_rele_and_unlock(dn, db, B_TRUE);
db->db_dnode_handle = NULL;

dbuf_hash_remove(db);
@@ -2467,8 +2432,10 @@ dbuf_destroy(dmu_buf_impl_t *db)
* If this dbuf is referenced from an indirect dbuf,
* decrement the ref count on the indirect dbuf.
*/
if (parent && parent != dndb)
dbuf_rele(parent, db);
if (parent && parent != dndb) {
mutex_enter(&parent->db_mtx);
dbuf_rele_and_unlock(parent, db, B_TRUE);
}
}

/*
@@ -3195,7 +3162,7 @@ void
dbuf_rele(dmu_buf_impl_t *db, void *tag)
{
mutex_enter(&db->db_mtx);
dbuf_rele_and_unlock(db, tag);
dbuf_rele_and_unlock(db, tag, B_FALSE);
}

void
@@ -3206,10 +3173,19 @@ dmu_buf_rele(dmu_buf_t *db, void *tag)

/*
* dbuf_rele() for an already-locked dbuf. This is necessary to allow
* db_dirtycnt and db_holds to be updated atomically.
* db_dirtycnt and db_holds to be updated atomically. The 'evicting'
* argument should be set if we are already in the dbuf-evicting code
* path, in which case we don't want to recursively evict. This allows us to
* avoid deeply nested stacks that would have a call flow similar to this:
*
* dbuf_rele()-->dbuf_rele_and_unlock()-->dbuf_evict_notify()
* ^ |
* | |
* +-----dbuf_destroy()<--dbuf_evict_one()<--------+
*
*/
void
dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag)
dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag, boolean_t evicting)
{
int64_t holds;

@@ -3310,7 +3286,8 @@ dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag)
refcount_count(&dbuf_cache_size));
mutex_exit(&db->db_mtx);

dbuf_evict_notify();
if (!evicting)
dbuf_evict_notify();
}

if (do_arc_evict)
@@ -3647,7 +3624,7 @@ dbuf_sync_leaf(dbuf_dirty_record_t *dr, dmu_tx_t *tx)
kmem_free(dr, sizeof (dbuf_dirty_record_t));
ASSERT(db->db_dirtycnt > 0);
db->db_dirtycnt -= 1;
dbuf_rele_and_unlock(db, (void *)(uintptr_t)txg);
dbuf_rele_and_unlock(db, (void *)(uintptr_t)txg, B_FALSE);
return;
}

@@ -4020,7 +3997,7 @@ dbuf_write_done(zio_t *zio, arc_buf_t *buf, void *vdb)
ASSERT(db->db_dirtycnt > 0);
db->db_dirtycnt -= 1;
db->db_data_pending = NULL;
dbuf_rele_and_unlock(db, (void *)(uintptr_t)tx->tx_txg);
dbuf_rele_and_unlock(db, (void *)(uintptr_t)tx->tx_txg, B_FALSE);
}

static void
@@ -1571,11 +1571,11 @@ void
dnode_rele(dnode_t *dn, void *tag)
{
mutex_enter(&dn->dn_mtx);
dnode_rele_and_unlock(dn, tag);
dnode_rele_and_unlock(dn, tag, B_FALSE);
}

void
dnode_rele_and_unlock(dnode_t *dn, void *tag)
dnode_rele_and_unlock(dnode_t *dn, void *tag, boolean_t evicting)
{
uint64_t refs;
/* Get while the hold prevents the dnode from moving. */
@@ -1606,7 +1606,8 @@ dnode_rele_and_unlock(dnode_t *dn, void *tag)
* that the handle has zero references, but that will be
* asserted anyway when the handle gets destroyed.
*/
dbuf_rele(db, dnh);
mutex_enter(&db->db_mtx);
dbuf_rele_and_unlock(db, dnh, evicting);
}
}

@@ -21,7 +21,7 @@

/*
* Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2012, 2017 by Delphix. All rights reserved.
* Copyright (c) 2012, 2018 by Delphix. All rights reserved.
* Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
*/

@@ -424,6 +424,19 @@ dnode_evict_dbufs(dnode_t *dn)
avl_insert_here(&dn->dn_dbufs, db_marker, db,
AVL_BEFORE);

/*
* We need to use the "marker" dbuf rather than
* simply getting the next dbuf, because
* dbuf_destroy() may actually remove multiple dbufs.
* It can call itself recursively on the parent dbuf,
* which may also be removed from dn_dbufs. The code
* flow would look like:
*
* dbuf_destroy():
* dnode_rele_and_unlock(parent_dbuf, evicting=TRUE):
* if (!cacheable || pending_evict)
* dbuf_destroy()
*/
dbuf_destroy(db);

db_next = AVL_NEXT(&dn->dn_dbufs, db_marker);
@@ -484,7 +497,7 @@ dnode_undirty_dbufs(list_t *list)
list_destroy(&dr->dt.di.dr_children);
}
kmem_free(dr, sizeof (dbuf_dirty_record_t));
dbuf_rele_and_unlock(db, (void *)(uintptr_t)txg);
dbuf_rele_and_unlock(db, (void *)(uintptr_t)txg, B_FALSE);
}
}

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