#include <sys/zfeature.h>
#include <sys/dsl_dataset.h>
+/*
+ * Each of the concurrent object allocators will grab
+ * 2^dmu_object_alloc_chunk_shift dnode slots at a time. The default is to
+ * grab 128 slots, which is 4 blocks worth. This was experimentally
+ * determined to be the lowest value that eliminates the measurable effect
+ * of lock contention from this code path.
+ */
+int dmu_object_alloc_chunk_shift = 7;
+
uint64_t
dmu_object_alloc(objset_t *os, dmu_object_type_t ot, int blocksize,
dmu_object_type_t bonustype, int bonuslen, dmu_tx_t *tx)
dnode_t *dn = NULL;
int dn_slots = dnodesize >> DNODE_SHIFT;
boolean_t restarted = B_FALSE;
+ uint64_t *cpuobj = &os->os_obj_next_percpu[CPU_SEQID %
+ os->os_obj_next_percpu_len];
+ int dnodes_per_chunk = 1 << dmu_object_alloc_chunk_shift;
if (dn_slots == 0) {
dn_slots = DNODE_MIN_SLOTS;
ASSERT3S(dn_slots, <=, DNODE_MAX_SLOTS);
}
- mutex_enter(&os->os_obj_lock);
+ /*
+ * The "chunk" of dnodes that is assigned to a CPU-specific
+ * allocator needs to be at least one block's worth, to avoid
+ * lock contention on the dbuf. It can be at most one L1 block's
+ * worth, so that the "rescan after polishing off a L1's worth"
+ * logic below will be sure to kick in.
+ */
+ if (dnodes_per_chunk < DNODES_PER_BLOCK)
+ dnodes_per_chunk = DNODES_PER_BLOCK;
+ if (dnodes_per_chunk > L1_dnode_count)
+ dnodes_per_chunk = L1_dnode_count;
+
+ object = *cpuobj;
for (;;) {
- object = os->os_obj_next;
/*
- * Each time we polish off a L1 bp worth of dnodes (2^12
- * objects), move to another L1 bp that's still
- * reasonably sparse (at most 1/4 full). Look from the
- * beginning at most once per txg. If we still can't
- * allocate from that L1 block, search for an empty L0
- * block, which will quickly skip to the end of the
- * metadnode if the no nearby L0 blocks are empty. This
- * fallback avoids a pathology where full dnode blocks
- * containing large dnodes appear sparse because they
- * have a low blk_fill, leading to many failed
- * allocation attempts. In the long term a better
- * mechanism to search for sparse metadnode regions,
- * such as spacemaps, could be implemented.
- *
- * os_scan_dnodes is set during txg sync if enough objects
- * have been freed since the previous rescan to justify
- * backfilling again.
- *
- * Note that dmu_traverse depends on the behavior that we use
- * multiple blocks of the dnode object before going back to
- * reuse objects. Any change to this algorithm should preserve
- * that property or find another solution to the issues
- * described in traverse_visitbp.
+ * If we finished a chunk of dnodes, get a new one from
+ * the global allocator.
*/
- if (P2PHASE(object, L1_dnode_count) == 0) {
- uint64_t offset;
- uint64_t blkfill;
- int minlvl;
- int error;
- if (os->os_rescan_dnodes) {
- offset = 0;
- os->os_rescan_dnodes = B_FALSE;
- } else {
- offset = object << DNODE_SHIFT;
+ if (P2PHASE(object, dnodes_per_chunk) == 0) {
+ mutex_enter(&os->os_obj_lock);
+ ASSERT0(P2PHASE(os->os_obj_next_chunk,
+ dnodes_per_chunk));
+ object = os->os_obj_next_chunk;
+
+ /*
+ * Each time we polish off a L1 bp worth of dnodes
+ * (2^12 objects), move to another L1 bp that's
+ * still reasonably sparse (at most 1/4 full). Look
+ * from the beginning at most once per txg. If we
+ * still can't allocate from that L1 block, search
+ * for an empty L0 block, which will quickly skip
+ * to the end of the metadnode if no nearby L0
+ * blocks are empty. This fallback avoids a
+ * pathology where full dnode blocks containing
+ * large dnodes appear sparse because they have a
+ * low blk_fill, leading to many failed allocation
+ * attempts. In the long term a better mechanism to
+ * search for sparse metadnode regions, such as
+ * spacemaps, could be implemented.
+ *
+ * os_scan_dnodes is set during txg sync if enough
+ * objects have been freed since the previous
+ * rescan to justify backfilling again.
+ *
+ * Note that dmu_traverse depends on the behavior
+ * that we use multiple blocks of the dnode object
+ * before going back to reuse objects. Any change
+ * to this algorithm should preserve that property
+ * or find another solution to the issues described
+ * in traverse_visitbp.
+ */
+ if (P2PHASE(object, L1_dnode_count) == 0) {
+ uint64_t offset;
+ uint64_t blkfill;
+ int minlvl;
+ int error;
+ if (os->os_rescan_dnodes) {
+ offset = 0;
+ os->os_rescan_dnodes = B_FALSE;
+ } else {
+ offset = object << DNODE_SHIFT;
+ }
+ blkfill = restarted ? 1 : DNODES_PER_BLOCK >> 2;
+ minlvl = restarted ? 1 : 2;
+ restarted = B_TRUE;
+ error = dnode_next_offset(DMU_META_DNODE(os),
+ DNODE_FIND_HOLE, &offset, minlvl,
+ blkfill, 0);
+ if (error == 0) {
+ object = offset >> DNODE_SHIFT;
+ }
}
- blkfill = restarted ? 1 : DNODES_PER_BLOCK >> 2;
- minlvl = restarted ? 1 : 2;
- restarted = B_TRUE;
- error = dnode_next_offset(DMU_META_DNODE(os),
- DNODE_FIND_HOLE, &offset, minlvl, blkfill, 0);
- if (error == 0)
- object = offset >> DNODE_SHIFT;
+ /*
+ * Note: if "restarted", we may find a L0 that
+ * is not suitably aligned.
+ */
+ os->os_obj_next_chunk =
+ P2ALIGN(object, dnodes_per_chunk) +
+ dnodes_per_chunk;
+ (void) atomic_swap_64(cpuobj, object);
+ mutex_exit(&os->os_obj_lock);
}
- os->os_obj_next = object + dn_slots;
/*
* XXX We should check for an i/o error here and return
* dmu_tx_assign(), but there is currently no mechanism
* to do so.
*/
- (void) dnode_hold_impl(os, object, DNODE_MUST_BE_FREE, dn_slots,
- FTAG, &dn);
- if (dn)
- break;
-
- if (dmu_object_next(os, &object, B_TRUE, 0) == 0)
- os->os_obj_next = object;
- else
+ (void) dnode_hold_impl(os, object, DNODE_MUST_BE_FREE,
+ dn_slots, FTAG, &dn);
+ if (dn != NULL) {
+ rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
/*
- * Skip to next known valid starting point for a dnode.
+ * Another thread could have allocated it; check
+ * again now that we have the struct lock.
*/
- os->os_obj_next = P2ROUNDUP(object + 1,
- DNODES_PER_BLOCK);
- }
-
- dnode_allocate(dn, ot, blocksize, 0, bonustype, bonuslen, dn_slots, tx);
- mutex_exit(&os->os_obj_lock);
-
- dmu_tx_add_new_object(tx, dn);
- dnode_rele(dn, FTAG);
+ if (dn->dn_type == DMU_OT_NONE) {
+ dnode_allocate(dn, ot, blocksize, 0,
+ bonustype, bonuslen, dn_slots, tx);
+ rw_exit(&dn->dn_struct_rwlock);
+ dmu_tx_add_new_object(tx, dn);
+ dnode_rele(dn, FTAG);
+
+ (void) atomic_swap_64(cpuobj,
+ object + dn_slots);
+ return (object);
+ }
+ rw_exit(&dn->dn_struct_rwlock);
+ dnode_rele(dn, FTAG);
+ }
- return (object);
+ if (dmu_object_next(os, &object, B_TRUE, 0) != 0) {
+ /*
+ * Skip to next known valid starting point for a
+ * dnode.
+ */
+ object = P2ROUNDUP(object + 1, DNODES_PER_BLOCK);
+ }
+ (void) atomic_swap_64(cpuobj, object);
+ }
}
int
EXPORT_SYMBOL(dmu_object_next);
EXPORT_SYMBOL(dmu_object_zapify);
EXPORT_SYMBOL(dmu_object_free_zapified);
+
+/* BEGIN CSTYLED */
+module_param(dmu_object_alloc_chunk_shift, int, 0644);
+MODULE_PARM_DESC(dmu_object_alloc_chunk_shift,
+ "CPU-specific allocator grabs 2^N objects at once");
+/* END CSTYLED */
#endif
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