Details
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Improvement
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Resolution: Fixed
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Major
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Upstream
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3
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9223372036854775807
Description
We tested MDT performance with and without changelogs enabled and observed a big performance impact with changelogs enabled.
pdsh -g mds 'lctl get_param mdd.*.changelog*' | dshbak -c ---------------- lmm1302 ---------------- mdd.lmm13-MDT0000.changelog_deniednext=60 mdd.lmm13-MDT0000.changelog_gc=1 mdd.lmm13-MDT0000.changelog_max_idle_indexes=2097446912 mdd.lmm13-MDT0000.changelog_max_idle_time=2592000 mdd.lmm13-MDT0000.changelog_min_free_cat_entries=2 mdd.lmm13-MDT0000.changelog_min_gc_interval=3600 mdd.lmm13-MDT0000.changelog_size=1637620216 mdd.lmm13-MDT0000.changelog_striped_dir_real_pfid=0 mdd.lmm13-MDT0000.changelog_current_mask= MARK CREAT MKDIR HLINK SLINK MKNOD UNLNK RMDIR RENME RNMTO LYOUT TRUNC SATTR XATTR HSM MTIME CTIME MIGRT FLRW RESYNC mdd.lmm13-MDT0000.changelog_mask= MARK CREAT MKDIR HLINK SLINK MKNOD UNLNK RMDIR RENME RNMTO LYOUT TRUNC SATTR XATTR HSM MTIME CTIME MIGRT FLRW RESYNC mdd.lmm13-MDT0000.changelog_users= current_index: 227636205 ID index (idle) mask cl3 219246813 (76) SUMMARY rate: (of 3 iterations) Operation Max Min Mean Std Dev --------- --- --- ---- ------- File creation : 64293.217 61191.096 62598.992 1282.215 File stat : 697756.541 690173.219 694512.173 3152.598 File read : 293942.923 292588.428 293054.714 615.889 File removal : 64479.412 57107.824 61776.225 3314.447 Tree creation : 169.033 145.318 154.133 10.595 Tree removal : 82.949 44.846 69.342 17.357 V-1: Entering PrintTimestamp... -- finished at 11/30/2023 12:19:44 --
When we disable changelog, performance comes back
# cscli lustre changelog disable lmm13-MDT0000: Deregistered changelog user #3 lmm13-MDT0001: Deregistered changelog user #3 SUMMARY rate: (of 3 iterations) Operation Max Min Mean Std Dev --------- --- --- ---- ------- File creation : 158468.362 153578.205 155692.937 2048.523 File stat : 703378.629 665431.521 689570.511 17093.925 File read : 290063.030 278902.768 284177.285 4568.720 File removal : 141796.451 136881.639 139915.690 2163.940 Tree creation : 199.212 131.040 173.177 30.070 Tree removal : 95.939 39.770 74.663 24.871 V-1: Entering PrintTimestamp... -- finished at 11/30/2023 12:23:45 --
I'v taken a perf report with changelog enabled, looks like llog_cat_add_rec()->mutex_lock is a bottle neck
--14.94%--mdt_reint_create
|
--14.93%--mdt_create
|
|--14.63%--mdd_create
| |
| |--12.85%--mdd_changelog_ns_store
| | |
| | --12.84%--mdd_changelog_store
| | |
| | --12.84%--llog_add
| | |
| | --12.84%--llog_cat_add_rec
| | |
| | |--12.70%--rwsem_down_write_slowpath
| | | |
| | | |--11.80%--osq_lock
| | | |
| | | --0.46%--rwsem_spin_on_owner
| | |
| | --0.12%--llog_write_rec
| | |
| | --0.12%--mdd_changelog_write_rec
Without changelog perf looks like
|--5.90%--mdd_create
|
|--4.74%--mdd_create_object
| |
| |--3.01%--mdd_create_object_internal
| | |
| | --3.01%--lod_create
| | |
| | --3.01%--lod_sub_create
| | |
| | --3.01%--osd_create
| | |
| | |--2.78%--osd_mkfile.constprop.104
| | | |
| | | --2.78%--ldiskfs_create_inode
| | | |
| | | --2.78%--__ldiskfs_new_inode
From a Lustre llog design/implementation, adding a record to changelog have a synchronization on down_wtrite(plain_llog->lgh_lock). It is a top semaphore.
All locking for a adding record looks next
down_write((&loghandle->lgh_lock) synchronize writers ----down_write(&loghandle->lgh_last_sem) synchronize write and parallel read --------mutex_lock(&loghandle->lgh_hdr_mutex) protects llog header/bitmap data from concurrent update/cancel --------dt_write_lock(env, o, 0); for atomic update header and record for a remote readers ----------- write header update --------mutex_unlock(&loghandle->lgh_hdr_mutex); --------write a record --------dt_write_unlock(env, o); ----up_write(&loghandle->lgh_last_sem); up_write(&loghandle->lgh_lock);
So there is a real limit for adding record at changelog, and all metadata threads, 512 or so, would sleep at a top semaphore during changelog adding. Only one could be a writer for a moment. Bottleneck.
Attachments
Issue Links
- is related to
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LU-19015 Possible records skipping during changelog processing when an ENOSPC occurred while writing a record
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- Open
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Activity
looking at
LU-18218mdd: changelog specific write function patch I still don't quite understand where the improvement comes from. the patch replaces the mutex with a spinlock, but there is outter down_write(&loghandle->lgh_last_sem).
With the patch, the "changelog add record" operation now utilizes its own dedicated function, mdd_changelog_write_rec(), to write a llog record, replacing the previous use of llog_osd_write_rec().
The key enhancement is the ability to perform parallel writes . The mdd_changelog_write_rec() function calculates the file offset and record index and releasing the &loghandle->lgh_lock. A semaphore is used to protect the offset/index calculation only, enabling dt_write() to execute concurrently. This reduces contention and improves efficiency.
looking at LU-18218 mdd: changelog specific write function patch I still don't quite understand where the improvement comes from. the patch replaces the mutex with a spinlock, but there is outter down_write(&loghandle->lgh_last_sem).
"Oleg Drokin <green@whamcloud.com>" merged in patch https://review.whamcloud.com/c/fs/lustre-release/+/56342/
Subject: LU-18218 mdd: changelog specific write function
Project: fs/lustre-release
Branch: master
Current Patch Set:
Commit: cb1290768df9fca6ead194c2812fb0182d85191c
"Oleg Drokin <green@whamcloud.com>" merged in patch https://review.whamcloud.com/c/fs/lustre-release/+/57920/
Subject: LU-18218 llog: repeat declare for remote obj
Project: fs/lustre-release
Branch: master
Current Patch Set:
Commit: 9b2de53f9b39f0e421e97e6a16a2f5998fe8cbfb
"Alexander Boyko <alexander.boyko@hpe.com>" uploaded a new patch: https://review.whamcloud.com/c/fs/lustre-release/+/57920
Subject: LU-18218 llog: repeat declare for remote obj
Project: fs/lustre-release
Branch: master
Current Patch Set: 1
Commit: ead97bde20156f50e9c21b0211170d60f98ae0fd
>not sure what have you reproduced, but I'm hitting this symptom:
the symptoms are ESTALE like you have
not sure what have you reproduced, but I'm hitting this symptom:
rm: cannot remove '/mnt/lustre/d60g.sanity/subdir1': Stale file handle rm: cannot remove '/mnt/lustre/d60g.sanity/subdir13': Stale file handle rm: cannot remove '/mnt/lustre/d60g.sanity/subdir21': Stale file handle sanity test_60g: @@@@@@ FAIL: rmdir failed
this is because of llog_declare_write_rec() you call for remote objects in llog_declare_write_rec() -> llog_declare_write_rec().
going to try a small patch..
I've reproduce 60g fail.
looks like transaction abort from test happened for llog osp file creation. And later it leads to ESTALE at llog_osd_declare_write_rec()
00080000:02000000:5.0:1737730681.616524:0:1162613:0:(osd_handler.c:2091:osd_trans_start()) *** cfs_fail_loc=19a, val=0*** 00080000:00000001:5.0:1737730681.616524:0:1162613:0:(osd_handler.c:2092:osd_trans_start()) Process leaving via out (rc=18446744073709551611 : -5 : 0xfffffffffffffffb) 00080000:00000001:5.0:1737730681.616525:0:1162613:0:(osd_handler.c:2119:osd_trans_start()) Process leaving (rc=18446744073709551611 : -5 : fffffffffffffffb) 00000020:00000001:5.0:1737730681.616525:0:1162613:0:(out_handler.c:903:out_tx_end()) Process leaving via stop (rc=18446744073709551611 : -5 : 0xfffffffffffffffb) 00080000:00000001:5.0:1737730681.616525:0:1162613:0:(osd_handler.c:2176:osd_trans_stop()) Process entered 00040000:00000001:5.0:1737730681.616526:0:1162613:0:(qsd_handler.c:1120:qsd_op_end()) Process entered 00040000:00000001:5.0:1737730681.616526:0:1162613:0:(qsd_handler.c:1151:qsd_op_end()) Process leaving 00080000:00000001:5.0:1737730681.616526:0:1162613:0:(osd_handler.c:2271:osd_trans_stop()) Process leaving (rc=0 : 0 : 0) 00000004:00000001:5.0:1737730681.616527:0:1162613:0:(mdt_handler.c:6840:mdt_object_free()) Process entered 00000004:00000040:5.0:1737730681.616527:0:1162613:0:(mdt_handler.c:6843:mdt_object_free()) object free, fid = [0x240000401:0x8cb0:0x0] 00000004:00000001:5.0:1737730681.616527:0:1162613:0:(mdt_handler.c:6854:mdt_object_free()) Process leaving 00000020:00000002:5.0:1737730681.616527:0:1162613:0:(lu_object.c:224:lu_object_put()) Add ffff98c42af76700/ffff98c42d0e0150 to site lru. bkt: ffff98c4320e5338 00000020:00000002:5.0:1737730681.616528:0:1162613:0:(lu_object.c:224:lu_object_put()) Add ffff98c42bcd4b00/ffff98c430506a80 to site lru. bkt: ffff98c4320e6670 00000020:00000001:5.0:1737730681.616528:0:1162613:0:(out_handler.c:944:out_tx_end()) Process leaving (rc=18446744073709551611 : -5 : fffffffffffffffb) 00000020:00000001:5.0:1737730681.616528:0:1162613:0:(out_handler.c:1275:out_handle()) Process leaving (rc=18446744073709551611 : -5 : fffffffffffffffb) 00010000:00000040:5.0:1737730681.616528:0:1162613:0:(ldlm_lib.c:3209:target_committed_to_req()) last_committed 4295177667, transno 0, xid 1822138016289024 00010000:00000001:5.0:1737730681.616529:0:1162613:0:(ldlm_lib.c:3279:target_send_reply()) Process entered 00010000:00000200:5.0:1737730681.616529:0:1162613:0:(ldlm_lib.c:3267:target_send_reply_msg()) @@@ sending reply req@ffff98c342d1c450 x1822138016289024/t0(0) o1000->lustre-MDT0000-mdtlov_UUID@0@lo:42/0 lens 1320/4320 e 0 to 0 dl 1737730692 ref 1 fl Interpret:/200/0 rc -5/0 job:'osp_up1-0.0' uid:0 gid:0 .... 00000100:00000001:5.0:1737730681.616576:0:1163369:0:(niobuf.c:447:ptlrpc_unregister_bulk()) Process entered 00000100:00000001:5.0:1737730681.616576:0:1163369:0:(niobuf.c:461:ptlrpc_unregister_bulk()) Process leaving (rc=1 : 1 : 1) 00000004:00000001:5.0:1737730681.616577:0:1163369:0:(osp_trans.c:600:osp_update_interpret()) Process entered 00000004:00080000:5.0:1737730681.616577:0:1163369:0:(osp_md_object.c:1164:osp_write_interpreter()) error [0x240000401:0x1:0x0]: rc = -5 00000004:00080000:5.0:1737730681.616577:0:1163369:0:(osp_md_object.c:1164:osp_write_interpreter()) error [0x240000401:0x1:0x0]: rc = -5 00000004:00080000:5.0:1737730681.616578:0:1163369:0:(osp_md_object.c:1164:osp_write_interpreter()) error [0x240000401:0x1:0x0]: rc = -5 00000004:00080000:5.0:1737730681.616578:0:1163369:0:(osp_md_object.c:1164:osp_write_interpreter()) error [0x240000401:0x1:0x0]: rc = -5 00000004:00000001:5.0:1737730681.616578:0:1163369:0:(osp_object.c:1374:osp_invalidate()) Process entered 00000004:00080000:5.0:1737730681.616578:0:1163369:0:(osp_object.c:1376:osp_invalidate()) Invalidate osp_object [0x240000401:0x1:0x0] 00000004:00000001:5.0:1737730681.616579:0:1163369:0:(osp_object.c:1396:osp_invalidate()) Process leaving (rc=0 : 0 : 0) 00000004:00000001:5.0:1737730681.616579:0:1163369:0:(osp_trans.c:689:osp_update_interpret()) Process leaving (rc=18446744073709551611 : -5 : fffffffffffffffb)
But the real problem for this llog fid [0x240000401:0x8cb0:0x0] happened early
00000020:00000001:5.0:1737730681.616457:0:1163628:0:(out_lib.c:251:out_attr_set_pack()) Process leaving (rc=0 : 0 : 0) 00000040:00001000:5.0:1737730681.616458:0:1163628:0:(llog_cat.c:186:llog_cat_new_log()) new plain log [0x240000401:0x8cb0:0x0].61 of catalog [0x240000401:0x1:0x0] 00000004:00000001:5.0:1737730681.616458:0:1163628:0:(osp_dev.c:793:osp_statfs()) Process entered 00000004:00001000:5.0:1737730681.616458:0:1163628:0:(osp_dev.c:808:osp_statfs()) lustre-MDT0001-osp-MDT0000: blocks=68640, bfree=17648, bavail=11756, bsize=4096, reserved_mb_low=1, reserved_mb_high=3, files=199976, ffree=199442, state=0 00000004:00000001:5.0:1737730681.616459:0:1163628:0:(osp_dev.c:816:osp_statfs()) Process leaving (rc=0 : 0 : 0) 00000004:00000001:5.0:1737730681.616459:0:1163628:0:(osp_trans.c:1555:osp_trans_stop()) Process entered 00000004:00080000:5.0:1737730681.616459:0:1163628:0:(osp_trans.c:1581:osp_trans_stop()) lustre-MDT0001-osp-MDT0000: add oth ffff98c42b331c00 with version 137317 00000004:00000001:5.0:1737730681.616460:0:1163628:0:(osp_trans.c:1603:osp_trans_stop()) Process leaving (rc=0 : 0 : 0) 00000040:00000001:5.0:1737730681.616460:0:1163628:0:(llog_cat.c:222:llog_cat_new_log()) Process leaving (rc=0 : 0 : 0) 00000040:00001000:5.0:1737730681.616460:0:1163628:0:(llog_cat.c:366:llog_cat_prep_log()) lustre-MDT0001-osp-MDT0000: open log [0x240000401:0x8cb0:0x0] for catalog [0x240000401:0x1:0x0] rc=0
this means that next logic is not work, there is no sync llog creation base on Lustre logs, and out request happened later at 1737730681.616525
if (dt_object_remote(cathandle->lgh_obj)) {
/* For remote operation, if we put the llog object
* creation in the current transaction, then the
* llog object will not be created on the remote
* target until the transaction stop, if other
* operations start before the transaction stop,
* and use the same llog object, will be dependent
* on the success of this transaction. So let's
* create the llog object synchronously here to
* remove the dependency.
*/
rc = llog_cat_new_log(env, cathandle, loghandle, NULL);
if (rc == -ESTALE) {
I guess because this check "if (likely(!list_empty(&our->our_list)))" is first, no matter how llog_cat_new_log() tries to do it sync (by handle->th_result to 0).
CDEBUG(D_HA, "%s: add oth %p with version %llu\n",
osp->opd_obd->obd_name, oth, our->our_version);
LASSERT(our->our_req_ready == 0);
spin_lock(&our->our_list_lock);
if (likely(!list_empty(&our->our_list))) {
/* notify sending thread */
our->our_req_ready = 1;
wake_up(&osp->opd_update->ou_waitq);
spin_unlock(&our->our_list_lock);
} else if (th->th_result == 0) {
/* if the request does not needs to be serialized,
* read-only request etc, let's send it right away */
spin_unlock(&our->our_list_lock);
rc = osp_send_update_req(env, osp, our);
} else {
spin_unlock(&our->our_list_lock);
osp_trans_callback(env, oth, th->th_result);
}
out:
osp_thandle_put(env, oth);
RETURN(rc);
bzzz any thoughts about fixing this?
Subject:
LU-18218llog: catalog lgh_lock refactoring
with this patch applied I hit a failure in sanity/60g:
# ONLY=60g MDSCOUNT=2 ONLY_REPEAT=1000 MDSSIZE=3000000 bash sanity.sh: [ 795.666375] Lustre: DEBUG MARKER: == sanity test 60g: transaction abort won't cause MDT hung (repeat 233/1000 iter, 12/ min) ========================================================== 07:31:05 (1737617465) ... /mnt/lustre/d60g.sanity/subdir97: rm: cannot remove '/mnt/lustre/d60g.sanity/subdir22': Stale file handle rm: cannot remove '/mnt/lustre/d60g.sanity/subdir14': Stale file handle rm: cannot remove '/mnt/lustre/d60g.sanity/subdir6': Stale file handle rm: cannot remove '/mnt/lustre/d60g.sanity/subdir32': Stale file handle sanity test_60g: @@@@@@ FAIL: rmdir failed [ 799.015419] Lustre: DEBUG MARKER: sanity test_60g: @@@@@@ FAIL: rmdir failed
it takes quite a while, but without the patch I'm unable to reproduce at all.
what would happen if a write to offset A fails while another write to offset B succeed where A > B ? while this is very unlikely, but still possible I think.