ep_kv_size != vb_active_itm_memory + vb_replica_itm_memory + vb_pending_itm_memory

hello,
we have 2 nodes in a cluster with replica enabled.
mem_used increased and items began to be ejected.
In order to limit disk IO, we change the value of ep_mem_low_wat and ep_mem_high_wat.

The problem is that vb_active_itm_memory decreases but mem_used and ep_kv_size didn't decrease enough.

Do you have any idea of the problem ?

Server 1:
ep_kv_size: 20336694480
ep_max_data_size: 60188262400
ep_mem_high_wat: 55000000000
ep_mem_low_wat: 52000000000
mem_used: 20659513297
vb_active_itm_memory: 9788261510
vb_pending_itm_memory: 0
vb_replica_itm_memory: 333461743
Server 2:
ep_kv_size: 53641447832
ep_max_data_size: 60188262400
ep_mem_high_wat: 55000000000
ep_mem_low_wat: 52000000000
mem_used: 54169448340
vb_active_itm_memory: 7811492591
vb_pending_itm_memory: 0
vb_replica_itm_memory: 2631742302

Full mbstats :
Server1 :
accepting_conns: 1
auth_cmds: 18216
auth_errors: 14
bucket_active_conns: 1
bucket_conns: 133
bytes_read: 15914128439596
bytes_written: 3985604346954
cas_badval: 5
cas_hits: 4
cas_misses: 0
cmd_flush: 9
cmd_get: 202544201
cmd_set: 40190937
conn_yields: 869641
connection_structures: 280
curr_connections: 235
curr_items: 735746
curr_items_tot: 995795
daemon_connections: 10
decr_hits: 10
decr_misses: 0
delete_hits: 157919
delete_misses: 631644
ep_bg_fetched: 92706
ep_bg_load: 23504536579
ep_bg_load_avg: 253538
ep_bg_max_load: 33715951
ep_bg_max_wait: 67624281
ep_bg_min_load: 11
ep_bg_min_wait: 17
ep_bg_num_samples: 92706
ep_bg_wait: 238820898105
ep_bg_wait_avg: 2576110
ep_commit_num: 96009
ep_commit_time: 91
ep_commit_time_total: 2495883
ep_data_age: 21679
ep_data_age_highwat: 201764
ep_db_cleaner_status: complete
ep_db_strategy: multiMTVBDB
ep_dbinit: 1
ep_dbname: /opt/membase/var/lib/membase/data/default-data/default
ep_dbshards: 4
ep_diskqueue_drain: 1923821
ep_diskqueue_fill: 3216866
ep_diskqueue_items: 1306029
ep_diskqueue_memory: 114930552
ep_diskqueue_pending: 8875522673
ep_expired: 6831961345
ep_flush_all: false
ep_flush_duration: 67633
ep_flush_duration_highwat: 201742
ep_flush_duration_total: 2822221
ep_flush_preempts: 0
ep_flusher_state: running
ep_flusher_todo: 918032
ep_io_num_read: 92706
ep_io_num_write: 39621407
ep_io_read_bytes: 1174624958
ep_io_write_bytes: 1076262004165
ep_item_begin_failed: 0
ep_item_commit_failed: 0
ep_item_flush_expired: 34415938
ep_item_flush_failed: 0
ep_items_rm_from_checkpoints: 107389430
ep_kv_size: 20336694480
ep_latency_arith_cmd: 30
ep_latency_get_cmd: 202640003
ep_latency_store_cmd: 40190981
ep_max_data_size: 60188262400
ep_max_txn_size: 1000
ep_mem_high_wat: 55000000000
ep_mem_low_wat: 52000000000
ep_min_data_age: 0
ep_num_active_non_resident: 0
ep_num_checkpoint_remover_runs: 573219
ep_num_eject_failures: 26177
ep_num_eject_replicas: 331521
ep_num_expiry_pager_runs: 796
ep_num_non_resident: 67845
ep_num_not_my_vbuckets: 3957
ep_num_pager_runs: 11444
ep_num_value_ejects: 842679
ep_onlineupdate: false
ep_onlineupdate_revert_add: 0
ep_onlineupdate_revert_delete: 0
ep_onlineupdate_revert_update: 0
ep_oom_errors: 0
ep_overhead: 322818817
ep_pending_ops: 0
ep_pending_ops_max: 0
ep_pending_ops_max_duration: 0
ep_pending_ops_total: 0
ep_queue_age_cap: 900
ep_queue_size: 388090
ep_storage_age: 21679
ep_storage_age_highwat: 201764
ep_storage_type: featured
ep_store_max_concurrency: 10
ep_store_max_readers: 9
ep_store_max_readwrite: 1
ep_tap_bg_fetch_requeued: 0
ep_tap_bg_fetched: 0
ep_tap_keepalive: 300
ep_tmp_oom_errors: 624159
ep_too_old: 37120299
ep_too_young: 0
ep_total_cache_size: 99510786981
ep_total_del_items: 27175531
ep_total_enqueued: 107292095
ep_total_new_items: 29440402
ep_total_persisted: 66796597
ep_uncommitted_items: 631
ep_value_size: 20154758771
ep_vb_total: 1024
ep_vbucket_del: 0
ep_vbucket_del_fail: 0
ep_version: 1.7.0_56_g8d17d20
ep_warmed_up: 0
ep_warmup: true
ep_warmup_dups: 0
ep_warmup_oom: 0
ep_warmup_thread: complete
ep_warmup_time: 12362
get_hits: 165412320
get_misses: 37131881
incr_hits: 20
incr_misses: 0
libevent: 2.0.11-stable
limit_maxbytes: 67108864
listen_disabled_num: 0
mem_used: 20659513297
pid: 14805
pointer_size: 64
rejected_conns: 0
rusage_system: 403203.018613
rusage_user: 200770.447368
tap_checkpoint_end_received: 4563041
tap_checkpoint_end_sent: 4835274
tap_checkpoint_start_received: 4576623
tap_checkpoint_start_sent: 4845443
tap_connect_received: 1033
tap_delete_received: 23538981
tap_delete_sent: 25940692
tap_flush_sent: 17
tap_mutation_received: 388662039
tap_mutation_sent: 137520654
tap_opaque_received: 22
tap_opaque_sent: 2066
tap_vbucket_set_sent: 2048
threads: 4
time: 1326833114
total_connections: 43140
uptime: 2866224
vb_active_curr_items: 735746
vb_active_eject: 511158
vb_active_ht_memory: 12836864
vb_active_itm_memory: 9788261510
vb_active_num: 512
vb_active_num_non_resident: 0
vb_active_ops_create: 448081
vb_active_ops_delete: 20266
vb_active_ops_reject: 0
vb_active_ops_update: 15789
vb_active_perc_mem_resident: 100
vb_active_queue_age: 20041103685000
vb_active_queue_drain: 1334450
vb_active_queue_fill: 2127889
vb_active_queue_memory: 69822632
vb_active_queue_pending: 6119212491
vb_active_queue_size: 793439
vb_dead_num: 0
vb_pending_curr_items: 0
vb_pending_eject: 0
vb_pending_ht_memory: 0
vb_pending_itm_memory: 0
vb_pending_num: 0
vb_pending_num_non_resident: 0
vb_pending_ops_create: 0
vb_pending_ops_delete: 0
vb_pending_ops_reject: 0
vb_pending_ops_update: 0
vb_pending_perc_mem_resident: 0
vb_pending_queue_age: 0
vb_pending_queue_drain: 0
vb_pending_queue_fill: 0
vb_pending_queue_memory: 0
vb_pending_queue_pending: 0
vb_pending_queue_size: 0
vb_replica_curr_items: 260049
vb_replica_eject: 331521
vb_replica_ht_memory: 12836864
vb_replica_itm_memory: 333461743
vb_replica_num: 512
vb_replica_num_non_resident: 67845
vb_replica_ops_create: 136889
vb_replica_ops_delete: 131
vb_replica_ops_reject: 0
vb_replica_ops_update: 104
vb_replica_perc_mem_resident: 73
vb_replica_queue_age: 17024677637000
vb_replica_queue_drain: 589371
vb_replica_queue_fill: 1088977
vb_replica_queue_memory: 45107920
vb_replica_queue_pending: 2756310182
vb_replica_queue_size: 512590
version: 1.4.4_461_gf99c147

Server2:
accepting_conns: 1
auth_cmds: 68933
auth_errors: 0
bucket_active_conns: 1
bucket_conns: 123
bytes_read: 6683777035162
bytes_written: 3944385500761
cas_badval: 1
cas_hits: 1
cas_misses: 0
cmd_flush: 9
cmd_get: 186240856
cmd_set: 35573333
conn_yields: 759146
connection_structures: 635
curr_connections: 235
curr_items: 704041
curr_items_tot: 1322787
daemon_connections: 10
decr_hits: 32
decr_misses: 0
delete_hits: 164155
delete_misses: 649755
ep_bg_fetched: 438971
ep_bg_load: 83877283633
ep_bg_load_avg: 191077
ep_bg_max_load: 23227772
ep_bg_max_wait: 80925225
ep_bg_min_load: 7
ep_bg_min_wait: 12
ep_bg_num_samples: 438971
ep_bg_wait: 1156308009837
ep_bg_wait_avg: 2634133
ep_commit_num: 165122
ep_commit_time: 11
ep_commit_time_total: 2526251
ep_data_age: 17068
ep_data_age_highwat: 99350
ep_db_cleaner_status: complete
ep_db_strategy: multiMTVBDB
ep_dbinit: 1
ep_dbname: /opt/membase/var/lib/membase/data/default-data/default
ep_dbshards: 4
ep_diskqueue_drain: 3595730
ep_diskqueue_fill: 3827625
ep_diskqueue_items: 1029192
ep_diskqueue_memory: 90568896
ep_diskqueue_pending: 9983975911
ep_expired: 2360197242
ep_flush_all: false
ep_flush_duration: 29199
ep_flush_duration_highwat: 58380
ep_flush_duration_total: 2768105
ep_flush_preempts: 0
ep_flusher_state: running
ep_flusher_todo: 565510
ep_io_num_read: 438971
ep_io_num_write: 46477831
ep_io_read_bytes: 5596563515
ep_io_write_bytes: 1482818728017
ep_item_begin_failed: 0
ep_item_commit_failed: 0
ep_item_flush_expired: 39146825
ep_item_flush_failed: 0
ep_items_rm_from_checkpoints: 111845763
ep_kv_size: 53641447832
ep_latency_arith_cmd: 52
ep_latency_get_cmd: 186679597
ep_latency_store_cmd: 35573387
ep_max_data_size: 60188262400
ep_max_txn_size: 1000
ep_mem_high_wat: 55000000000
ep_mem_low_wat: 52000000000
ep_min_data_age: 0
ep_num_active_non_resident: 195229
ep_num_checkpoint_remover_runs: 571980
ep_num_eject_failures: 59713
ep_num_eject_replicas: 2255313
ep_num_expiry_pager_runs: 794
ep_num_non_resident: 623033
ep_num_not_my_vbuckets: 0
ep_num_pager_runs: 9413
ep_num_value_ejects: 3736714
ep_onlineupdate: false
ep_onlineupdate_revert_add: 0
ep_onlineupdate_revert_delete: 0
ep_onlineupdate_revert_update: 0
ep_oom_errors: 0
ep_overhead: 528000508
ep_pending_ops: 0
ep_pending_ops_max: 0
ep_pending_ops_max_duration: 0
ep_pending_ops_total: 0
ep_queue_age_cap: 900
ep_queue_size: 476462
ep_storage_age: 17068
ep_storage_age_highwat: 99350
ep_storage_type: featured
ep_store_max_concurrency: 10
ep_store_max_readers: 9
ep_store_max_readwrite: 1
ep_tap_bg_fetch_requeued: 0
ep_tap_bg_fetched: 0
ep_tap_keepalive: 300
ep_tmp_oom_errors: 205882
ep_too_old: 41966459
ep_too_young: 0
ep_total_cache_size: 135260814877
ep_total_del_items: 31887022
ep_total_enqueued: 110441500
ep_total_new_items: 35665787
ep_total_persisted: 78360518
ep_uncommitted_items: 288
ep_value_size: 53400952337
ep_vb_total: 1024
ep_vbucket_del: 0
ep_vbucket_del_fail: 0
ep_version: 1.7.0_56_g8d17d20
ep_warmed_up: 0
ep_warmup: true
ep_warmup_dups: 0
ep_warmup_oom: 0
ep_warmup_thread: complete
ep_warmup_time: 12841
get_hits: 151019170
get_misses: 35221686
incr_hits: 17
incr_misses: 3
libevent: 2.0.11-stable
limit_maxbytes: 67108864
listen_disabled_num: 0
mem_used: 54169448340
pid: 2876
pointer_size: 64
rejected_conns: 0
rusage_system: 186242.315417
rusage_user: 164383.813346
tap_checkpoint_end_received: 4830300
tap_checkpoint_end_sent: 4558060
tap_checkpoint_start_received: 4840469
tap_checkpoint_start_sent: 4571642
tap_connect_received: 8
tap_delete_received: 25940670
tap_delete_sent: 23538951
tap_flush_received: 17
tap_flush_sent: 26
tap_mutation_received: 132777732
tap_mutation_sent: 384369463
tap_opaque_received: 2073
tap_opaque_sent: 16
tap_vbucket_set_received: 2048
threads: 4
time: 1326827312
total_connections: 93754
uptime: 2860070
vb_active_curr_items: 704041
vb_active_eject: 1481401
vb_active_ht_memory: 12836864
vb_active_itm_memory: 7811492591
vb_active_num: 512
vb_active_num_non_resident: 195229
vb_active_ops_create: 560502
vb_active_ops_delete: 16976
vb_active_ops_reject: 0
vb_active_ops_update: 47508
vb_active_perc_mem_resident: 72
vb_active_queue_age: 7939953381000
vb_active_queue_drain: 1919634
vb_active_queue_fill: 2020325
vb_active_queue_memory: 53258568
vb_active_queue_pending: 4333745647
vb_active_queue_size: 605211
vb_dead_num: 0
vb_pending_curr_items: 0
vb_pending_eject: 0
vb_pending_ht_memory: 0
vb_pending_itm_memory: 0
vb_pending_num: 0
vb_pending_num_non_resident: 0
vb_pending_ops_create: 0
vb_pending_ops_delete: 0
vb_pending_ops_reject: 0
vb_pending_ops_update: 0
vb_pending_perc_mem_resident: 0
vb_pending_queue_age: 0
vb_pending_queue_drain: 0
vb_pending_queue_fill: 0
vb_pending_queue_memory: 0
vb_pending_queue_pending: 0
vb_pending_queue_size: 0
vb_replica_curr_items: 618746
vb_replica_eject: 2255313
vb_replica_ht_memory: 12836864
vb_replica_itm_memory: 2631742302
vb_replica_num: 512
vb_replica_num_non_resident: 427804
vb_replica_ops_create: 615911
vb_replica_ops_delete: 123587
vb_replica_ops_reject: 0
vb_replica_ops_update: 74634
vb_replica_perc_mem_resident: 30
vb_replica_queue_age: 5495160029000
vb_replica_queue_drain: 1676096
vb_replica_queue_fill: 1807300
vb_replica_queue_memory: 37310328
vb_replica_queue_pending: 5650230264
vb_replica_queue_size: 423981
version: 1.4.4_461_gf99c147