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Improved dnode allocation and dmu_hold_impl() (#6611)

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Refactor dmu_object_alloc_dnsize() and dnode_hold_impl() to simplify the
code, fix errors introduced by commit dbeb879 (PR #6117) interacting
badly with large dnodes, and improve performance.

* When allocating a new dnode in dmu_object_alloc_dnsize(), update the
percpu object ID for the core's metadnode chunk immediately.  This
eliminates most lock contention when taking the hold and creating the
dnode.

* Correct detection of the chunk boundary to work properly with large
dnodes.

* Separate the dmu_hold_impl() code for the FREE case from the code for
the ALLOCATED case to make it easier to read.

* Fully populate the dnode handle array immediately after reading a
block of the metadnode from disk.  Subsequently the dnode handle array
provides enough information to determine which dnode slots are in use
and which are free.

* Add several kstats to allow the behavior of the code to be examined.

* Verify dnode packing in large_dnode_008_pos.ksh.  Since the test is
purely creates, it should leave very few holes in the metadnode.

* Add test large_dnode_009_pos.ksh, which performs concurrent creates
and deletes, to complement existing test which does only creates.

With the above fixes, there is very little contention in a test of about
200,000 racing dnode allocations produced by tests 'large_dnode_008_pos'
and 'large_dnode_009_pos'.

name                            type data
dnode_hold_dbuf_hold            4    0
dnode_hold_dbuf_read            4    0
dnode_hold_alloc_hits           4    3804690
dnode_hold_alloc_misses         4    216
dnode_hold_alloc_interior       4    3
dnode_hold_alloc_lock_retry     4    0
dnode_hold_alloc_lock_misses    4    0
dnode_hold_alloc_type_none      4    0
dnode_hold_free_hits            4    203105
dnode_hold_free_misses          4    4
dnode_hold_free_lock_misses     4    0
dnode_hold_free_lock_retry      4    0
dnode_hold_free_overflow        4    0
dnode_hold_free_refcount        4    57
dnode_hold_free_txg             4    0
dnode_allocate                  4    203154
dnode_reallocate                4    0
dnode_buf_evict                 4    23918
dnode_alloc_next_chunk          4    4887
dnode_alloc_race                4    0
dnode_alloc_next_block          4    18

The performance is slightly improved for concurrent creates with
16+ threads, and unchanged for low thread counts.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
This commit is contained in:
Giuseppe Di Natale
2017-09-13 15:46:15 -07:00
committed by Tony Hutter
parent 89950722c6
commit 45d1abc74d
9 changed files with 616 additions and 258 deletions
Download Patch File Download Diff File Expand all files Collapse all files
include/sys/dnode.h
+136
View File
@@ -100,6 +100,13 @@ extern "C" {
#define DN_ZERO_BONUSLEN (DN_BONUS_SIZE(DNODE_MAX_SIZE) + 1)
#define DN_KILL_SPILLBLK (1)
#define DN_SLOT_UNINIT ((void *)NULL) /* Uninitialized */
#define DN_SLOT_FREE ((void *)1UL) /* Free slot */
#define DN_SLOT_ALLOCATED ((void *)2UL) /* Allocated slot */
#define DN_SLOT_INTERIOR ((void *)3UL) /* Interior allocated slot */
#define DN_SLOT_IS_PTR(dn) ((void *)dn > DN_SLOT_INTERIOR)
#define DN_SLOT_IS_VALID(dn) ((void *)dn != NULL)
#define DNODES_PER_BLOCK_SHIFT (DNODE_BLOCK_SHIFT - DNODE_SHIFT)
#define DNODES_PER_BLOCK (1ULL << DNODES_PER_BLOCK_SHIFT)
@@ -363,6 +370,135 @@ void dnode_evict_bonus(dnode_t *dn);
((_dn)->dn_objset->os_primary_cache == ZFS_CACHE_ALL || \
(_dn)->dn_objset->os_primary_cache == ZFS_CACHE_METADATA)
/*
* Used for dnodestats kstat.
*/
typedef struct dnode_stats {
/*
* Number of failed attempts to hold a meta dnode dbuf.
*/
kstat_named_t dnode_hold_dbuf_hold;
/*
* Number of failed attempts to read a meta dnode dbuf.
*/
kstat_named_t dnode_hold_dbuf_read;
/*
* Number of times dnode_hold(..., DNODE_MUST_BE_ALLOCATED) was able
* to hold the requested object number which was allocated. This is
* the common case when looking up any allocated object number.
*/
kstat_named_t dnode_hold_alloc_hits;
/*
* Number of times dnode_hold(..., DNODE_MUST_BE_ALLOCATED) was not
* able to hold the request object number because it was not allocated.
*/
kstat_named_t dnode_hold_alloc_misses;
/*
* Number of times dnode_hold(..., DNODE_MUST_BE_ALLOCATED) was not
* able to hold the request object number because the object number
* refers to an interior large dnode slot.
*/
kstat_named_t dnode_hold_alloc_interior;
/*
* Number of times dnode_hold(..., DNODE_MUST_BE_ALLOCATED) needed
* to retry acquiring slot zrl locks due to contention.
*/
kstat_named_t dnode_hold_alloc_lock_retry;
/*
* Number of times dnode_hold(..., DNODE_MUST_BE_ALLOCATED) did not
* need to create the dnode because another thread did so after
* dropping the read lock but before acquiring the write lock.
*/
kstat_named_t dnode_hold_alloc_lock_misses;
/*
* Number of times dnode_hold(..., DNODE_MUST_BE_ALLOCATED) found
* a free dnode instantiated by dnode_create() but not yet allocated
* by dnode_allocate().
*/
kstat_named_t dnode_hold_alloc_type_none;
/*
* Number of times dnode_hold(..., DNODE_MUST_BE_FREE) was able
* to hold the requested range of free dnode slots.
*/
kstat_named_t dnode_hold_free_hits;
/*
* Number of times dnode_hold(..., DNODE_MUST_BE_FREE) was not
* able to hold the requested range of free dnode slots because
* at least one slot was allocated.
*/
kstat_named_t dnode_hold_free_misses;
/*
* Number of times dnode_hold(..., DNODE_MUST_BE_FREE) was not
* able to hold the requested range of free dnode slots because
* after acquiring the zrl lock at least one slot was allocated.
*/
kstat_named_t dnode_hold_free_lock_misses;
/*
* Number of times dnode_hold(..., DNODE_MUST_BE_FREE) needed
* to retry acquiring slot zrl locks due to contention.
*/
kstat_named_t dnode_hold_free_lock_retry;
/*
* Number of times dnode_hold(..., DNODE_MUST_BE_FREE) requested
* a range of dnode slots which were held by another thread.
*/
kstat_named_t dnode_hold_free_refcount;
/*
* Number of times dnode_hold(..., DNODE_MUST_BE_FREE) requested
* a range of dnode slots which would overflow the dnode_phys_t.
*/
kstat_named_t dnode_hold_free_overflow;
/*
* Number of times a dnode_hold(...) was attempted on a dnode
* which had already been unlinked in an earlier txg.
*/
kstat_named_t dnode_hold_free_txg;
/*
* Number of new dnodes allocated by dnode_allocate().
*/
kstat_named_t dnode_allocate;
/*
* Number of dnodes re-allocated by dnode_reallocate().
*/
kstat_named_t dnode_reallocate;
/*
* Number of meta dnode dbufs evicted.
*/
kstat_named_t dnode_buf_evict;
/*
* Number of times dmu_object_alloc*() reached the end of the existing
* object ID chunk and advanced to a new one.
*/
kstat_named_t dnode_alloc_next_chunk;
/*
* Number of times multiple threads attempted to allocate a dnode
* from the same block of free dnodes.
*/
kstat_named_t dnode_alloc_race;
/*
* Number of times dmu_object_alloc*() was forced to advance to the
* next meta dnode dbuf due to an error from dmu_object_next().
*/
kstat_named_t dnode_alloc_next_block;
/*
* Statistics for tracking dnodes which have been moved.
*/
kstat_named_t dnode_move_invalid;
kstat_named_t dnode_move_recheck1;
kstat_named_t dnode_move_recheck2;
kstat_named_t dnode_move_special;
kstat_named_t dnode_move_handle;
kstat_named_t dnode_move_rwlock;
kstat_named_t dnode_move_active;
} dnode_stats_t;
extern dnode_stats_t dnode_stats;
#define DNODE_STAT_INCR(stat, val) \
atomic_add_64(&dnode_stats.stat.value.ui64, (val));
#define DNODE_STAT_BUMP(stat) \
DNODE_STAT_INCR(stat, 1);
#ifdef ZFS_DEBUG
/*