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Reduce dirty records memory usage
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Small block workloads may use a very large number of dirty records.
During simple block cloning test due to BRT still using 4KB blocks
I can easily see up to 2.5M of those used.  Before this change
dbuf_dirty_record_t structures representing them were allocated via
kmem_zalloc(), that rounded their size up to 512 bytes.

Introduction of specialized kmem cache allows to reduce the size
from 512 to 408 bytes.  Additionally, since override and raw params
in dirty records are mutually exclusive, puting them into a union
allows to reduce structure size down to 368 bytes, increasing the
saving to 28%, that can be a 0.5GB or more of RAM.

Signed-off-by:	Alexander Motin <[email protected]>
Sponsored by:	iXsystems, Inc.
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@amotin
amotin committed Oct 28, 2024
1 parent e5d1f68 commit 903dea0
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Showing 5 changed files with 39 additions and 20 deletions.
26 changes: 17 additions & 9 deletions include/sys/dbuf.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -171,22 +171,28 @@ typedef struct dbuf_dirty_record {
* gets COW'd in a subsequent transaction group.
*/
arc_buf_t *dr_data;
blkptr_t dr_overridden_by;
override_states_t dr_override_state;
uint8_t dr_copies;
boolean_t dr_nopwrite;
boolean_t dr_brtwrite;
boolean_t dr_diowrite;
boolean_t dr_has_raw_params;

/*
* If dr_has_raw_params is set, the following crypt
* params will be set on the BP that's written.
*/
boolean_t dr_byteorder;
uint8_t dr_salt[ZIO_DATA_SALT_LEN];
uint8_t dr_iv[ZIO_DATA_IV_LEN];
uint8_t dr_mac[ZIO_DATA_MAC_LEN];
/* Override and raw params are mutually exclusive. */
union {
blkptr_t dr_overridden_by;
struct {
/*
* If dr_has_raw_params is set, the
* following crypt params will be set
* on the BP that's written.
*/
boolean_t dr_byteorder;
uint8_t dr_salt[ZIO_DATA_SALT_LEN];
uint8_t dr_iv[ZIO_DATA_IV_LEN];
uint8_t dr_mac[ZIO_DATA_MAC_LEN];
};
};
} dl;
struct dirty_lightweight_leaf {
/*
Expand Down Expand Up @@ -346,6 +352,8 @@ typedef struct dbuf_hash_table {

typedef void (*dbuf_prefetch_fn)(void *, uint64_t, uint64_t, boolean_t);

extern kmem_cache_t *dbuf_dirty_kmem_cache;

uint64_t dbuf_whichblock(const struct dnode *di, const int64_t level,
const uint64_t offset);

Expand Down
21 changes: 16 additions & 5 deletions module/zfs/dbuf.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -182,6 +182,7 @@ static void dbuf_sync_leaf_verify_bonus_dnode(dbuf_dirty_record_t *dr);
* Global data structures and functions for the dbuf cache.
*/
static kmem_cache_t *dbuf_kmem_cache;
kmem_cache_t *dbuf_dirty_kmem_cache;
static taskq_t *dbu_evict_taskq;

static kthread_t *dbuf_cache_evict_thread;
Expand Down Expand Up @@ -966,6 +967,8 @@ dbuf_init(void)
dbuf_kmem_cache = kmem_cache_create("dmu_buf_impl_t",
sizeof (dmu_buf_impl_t),
0, dbuf_cons, dbuf_dest, NULL, NULL, NULL, 0);
dbuf_dirty_kmem_cache = kmem_cache_create("dbuf_dirty_record_t",
sizeof (dbuf_dirty_record_t), 0, NULL, NULL, NULL, NULL, NULL, 0);

for (int i = 0; i < hmsize; i++)
mutex_init(&h->hash_mutexes[i], NULL, MUTEX_NOLOCKDEP, NULL);
Expand Down Expand Up @@ -1041,6 +1044,7 @@ dbuf_fini(void)
sizeof (kmutex_t));

kmem_cache_destroy(dbuf_kmem_cache);
kmem_cache_destroy(dbuf_dirty_kmem_cache);
taskq_destroy(dbu_evict_taskq);

mutex_enter(&dbuf_evict_lock);
Expand Down Expand Up @@ -2343,7 +2347,8 @@ dbuf_dirty(dmu_buf_impl_t *db, dmu_tx_t *tx)
* to make a copy of it so that the changes we make in this
* transaction group won't leak out when we sync the older txg.
*/
dr = kmem_zalloc(sizeof (dbuf_dirty_record_t), KM_SLEEP);
dr = kmem_cache_alloc(dbuf_dirty_kmem_cache, KM_SLEEP);
memset(dr, 0, sizeof (*dr));
list_link_init(&dr->dr_dirty_node);
list_link_init(&dr->dr_dbuf_node);
dr->dr_dnode = dn;
Expand Down Expand Up @@ -2526,7 +2531,7 @@ dbuf_undirty_bonus(dbuf_dirty_record_t *dr)
mutex_destroy(&dr->dt.di.dr_mtx);
list_destroy(&dr->dt.di.dr_children);
}
kmem_free(dr, sizeof (dbuf_dirty_record_t));
kmem_cache_free(dbuf_dirty_kmem_cache, dr);
ASSERT3U(db->db_dirtycnt, >, 0);
db->db_dirtycnt -= 1;
}
Expand Down Expand Up @@ -2616,7 +2621,7 @@ dbuf_undirty(dmu_buf_impl_t *db, dmu_tx_t *tx)
}
}

kmem_free(dr, sizeof (dbuf_dirty_record_t));
kmem_cache_free(dbuf_dirty_kmem_cache, dr);

ASSERT(db->db_dirtycnt > 0);
db->db_dirtycnt -= 1;
Expand Down Expand Up @@ -2941,7 +2946,7 @@ dmu_buf_set_crypt_params(dmu_buf_t *db_fake, boolean_t byteorder,
* (see dbuf_sync_dnode_leaf_crypt()).
*/
ASSERT3U(db->db.db_object, ==, DMU_META_DNODE_OBJECT);
ASSERT3U(db->db_level, ==, 0);
ASSERT0(db->db_level);
ASSERT(db->db_objset->os_raw_receive);

dmu_buf_will_dirty_impl(db_fake,
Expand All @@ -2950,6 +2955,7 @@ dmu_buf_set_crypt_params(dmu_buf_t *db_fake, boolean_t byteorder,
dr = dbuf_find_dirty_eq(db, tx->tx_txg);

ASSERT3P(dr, !=, NULL);
ASSERT3U(dr->dt.dl.dr_override_state, ==, DR_NOT_OVERRIDDEN);

dr->dt.dl.dr_has_raw_params = B_TRUE;
dr->dt.dl.dr_byteorder = byteorder;
Expand All @@ -2964,10 +2970,14 @@ dbuf_override_impl(dmu_buf_impl_t *db, const blkptr_t *bp, dmu_tx_t *tx)
struct dirty_leaf *dl;
dbuf_dirty_record_t *dr;

ASSERT3U(db->db.db_object, !=, DMU_META_DNODE_OBJECT);
ASSERT0(db->db_level);

dr = list_head(&db->db_dirty_records);
ASSERT3P(dr, !=, NULL);
ASSERT3U(dr->dr_txg, ==, tx->tx_txg);
dl = &dr->dt.dl;
ASSERT0(dl->dr_has_raw_params);
dl->dr_overridden_by = *bp;
dl->dr_override_state = DR_OVERRIDDEN;
BP_SET_LOGICAL_BIRTH(&dl->dr_overridden_by, dr->dr_txg);
Expand Down Expand Up @@ -3038,6 +3048,7 @@ dmu_buf_write_embedded(dmu_buf_t *dbuf, void *data,

dr = list_head(&db->db_dirty_records);
ASSERT3P(dr, !=, NULL);
ASSERT0(dl->dr_has_raw_params);
ASSERT3U(dr->dr_txg, ==, tx->tx_txg);
dl = &dr->dt.dl;
encode_embedded_bp_compressed(&dl->dr_overridden_by,
Expand Down Expand Up @@ -5083,7 +5094,7 @@ dbuf_write_done(zio_t *zio, arc_buf_t *buf, void *vdb)
dsl_pool_undirty_space(dmu_objset_pool(os), dr->dr_accounted,
zio->io_txg);

kmem_free(dr, sizeof (dbuf_dirty_record_t));
kmem_cache_free(dbuf_dirty_kmem_cache, dr);
}

static void
Expand Down
9 changes: 4 additions & 5 deletions module/zfs/dmu.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1895,6 +1895,7 @@ dmu_sync_done(zio_t *zio, arc_buf_t *buf, void *varg)
mutex_enter(&db->db_mtx);
ASSERT(dr->dt.dl.dr_override_state == DR_IN_DMU_SYNC);
if (zio->io_error == 0) {
ASSERT0(dr->dt.dl.dr_has_raw_params);
dr->dt.dl.dr_nopwrite = !!(zio->io_flags & ZIO_FLAG_NOPWRITE);
if (dr->dt.dl.dr_nopwrite) {
blkptr_t *bp = zio->io_bp;
Expand Down Expand Up @@ -2190,6 +2191,7 @@ dmu_sync(zio_t *pio, uint64_t txg, dmu_sync_cb_t *done, zgd_t *zgd)
return (SET_ERROR(EALREADY));
}

ASSERT0(dr->dt.dl.dr_has_raw_params);
ASSERT(dr->dt.dl.dr_override_state == DR_NOT_OVERRIDDEN);
dr->dt.dl.dr_override_state = DR_IN_DMU_SYNC;
mutex_exit(&db->db_mtx);
Expand Down Expand Up @@ -2657,6 +2659,7 @@ dmu_brt_clone(objset_t *os, uint64_t object, uint64_t offset, uint64_t length,
db = (dmu_buf_impl_t *)dbuf;
bp = &bps[i];

ASSERT3U(db->db.db_object, !=, DMU_META_DNODE_OBJECT);
ASSERT0(db->db_level);
ASSERT(db->db_blkid != DMU_BONUS_BLKID);
ASSERT(db->db_blkid != DMU_SPILL_BLKID);
Expand All @@ -2672,11 +2675,6 @@ dmu_brt_clone(objset_t *os, uint64_t object, uint64_t offset, uint64_t length,
db = (dmu_buf_impl_t *)dbuf;
bp = &bps[i];

ASSERT0(db->db_level);
ASSERT(db->db_blkid != DMU_BONUS_BLKID);
ASSERT(db->db_blkid != DMU_SPILL_BLKID);
ASSERT(BP_IS_HOLE(bp) || dbuf->db_size == BP_GET_LSIZE(bp));

dmu_buf_will_clone_or_dio(dbuf, tx);

mutex_enter(&db->db_mtx);
Expand All @@ -2685,6 +2683,7 @@ dmu_brt_clone(objset_t *os, uint64_t object, uint64_t offset, uint64_t length,
VERIFY(dr != NULL);
ASSERT3U(dr->dr_txg, ==, tx->tx_txg);
dl = &dr->dt.dl;
ASSERT0(dl->dr_has_raw_params);
dl->dr_overridden_by = *bp;
if (!BP_IS_HOLE(bp) || BP_GET_LOGICAL_BIRTH(bp) != 0) {
if (!BP_IS_EMBEDDED(bp)) {
Expand Down
1 change: 1 addition & 0 deletions module/zfs/dmu_direct.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -180,6 +180,7 @@ dmu_write_direct(zio_t *pio, dmu_buf_impl_t *db, abd_t *data, dmu_tx_t *tx)
if (list_next(&db->db_dirty_records, dr_head) != NULL)
zp.zp_nopwrite = B_FALSE;

ASSERT0(dr_head->dt.dl.dr_has_raw_params);
ASSERT3S(dr_head->dt.dl.dr_override_state, ==, DR_NOT_OVERRIDDEN);
dr_head->dt.dl.dr_override_state = DR_IN_DMU_SYNC;

Expand Down
2 changes: 1 addition & 1 deletion module/zfs/dnode_sync.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -566,7 +566,7 @@ dnode_undirty_dbufs(list_t *list)
mutex_destroy(&dr->dt.di.dr_mtx);
list_destroy(&dr->dt.di.dr_children);
}
kmem_free(dr, sizeof (dbuf_dirty_record_t));
kmem_cache_free(dbuf_dirty_kmem_cache, dr);
dbuf_rele_and_unlock(db, (void *)(uintptr_t)txg, B_FALSE);
}
}
Expand Down

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