Actions
Bug #3331
closed
deferred frees should happen after sync_pass 1
Start date:
2012-10-31
Due date:
% Done:
0%
Estimated time:
Difficulty:
Medium
Tags:
needs-triage
Gerrit CR:
External Bug:
Description
From George Wilson's original bug report at Delphix:
Today, we allow spa_sync() to process frees in both sync pass 1 and 2. Looking
at dcenter we can see that this is causing us to take longer to reach sync
convergence:
pass 1 45350KB 326ms (65%) [avg size 78KB]
pass 2 1171KB 29ms ( 5%) [avg size 26KB]
pass 3 221KB 41ms ( 8%) [avg size 4KB]
pass > 3 1941KB 82ms (16%) [avg size 21KB]
metaslab_sync 0KB 1ms ( 0%) [avg size 0KB]
metaslab_sync_done 0KB 2ms ( 0%) [avg size 0KB]
other 0KB 6ms ( 1%) [avg size 0KB]
spa_free_sync_cb 0KB 10ms ( 2%) [avg size 0KB]
spa_sync(txg=2926592) took 498ms (7 passes)
pass 1 46982KB 338ms (53%) [avg size 77KB]
pass 2 1419KB 39ms ( 6%) [avg size 24KB]
pass 3 244KB 35ms ( 5%) [avg size 3KB]
pass > 3 1944KB 204ms (32%) [avg size 19KB]
metaslab_sync 0KB 1ms ( 0%) [avg size 0KB]
metaslab_sync_done 0KB 2ms ( 0%) [avg size 0KB]
other 0KB 5ms ( 0%) [avg size 0KB]
spa_free_sync_cb 0KB 9ms ( 1%) [avg size 0KB]
spa_sync(txg=2926593) took 637ms (7 passes)
We can see that it's taking 7 sync passes to converge and we're writing about
2MB of data in passes > 3 (with an avg I/O size of 20KB).
Changing the SYNC_PASS_DEFERRED_FREE value from 2 to 1 we see the following:
pass 1 43373KB 270ms (70%) [avg size 79KB]
pass 2 1110KB 42ms (11%) [avg size 20KB]
pass 3 156KB 24ms ( 6%) [avg size 4KB]
pass > 3 156KB 29ms ( 7%) [avg size 4KB]
metaslab_sync 0KB 1ms ( 0%) [avg size 0KB]
metaslab_sync_done 0KB 2ms ( 0%) [avg size 0KB]
other 0KB 4ms ( 1%) [avg size 0KB]
spa_free_sync_cb 0KB 8ms ( 2%) [avg size 0KB]
spa_sync(txg=2926617) took 383ms (4 passes)
pass 1 46855KB 242ms (68%) [avg size 77KB]
pass 2 1337KB 40ms (11%) [avg size 22KB]
pass 3 161KB 23ms ( 6%) [avg size 4KB]
pass > 3 161KB 25ms ( 7%) [avg size 4KB]
metaslab_sync 0KB 1ms ( 0%) [avg size 0KB]
metaslab_sync_done 0KB 2ms ( 0%) [avg size 0KB]
other 0KB 6ms ( 1%) [avg size 0KB]
spa_free_sync_cb 0KB 11ms ( 3%) [avg size 0KB]
spa_sync(txg=2926618) took 352ms (4 passes)
Now it's taking 4 passes to converge and we're only writing out about 159KB
after sync pass 3 (avg I/O size of 4KB).
Related issues
Updated by Christopher Siden almost 11 years ago
- Status changed from In Progress to Closed
commit 01f55e48fb4d524eaf70687728aa51b7762e2e97
Author: George Wilson <george.wilson@delphix.com>
Date: Wed Nov 7 14:05:17 2012 -0800
3329 spa_sync() spends 10-20% of its time in spa_free_sync_cb()
3330 space_seg_t should have its own kmem_cache
3331 deferred frees should happen after sync_pass 1
3335 make SYNC_PASS_* constants tunable
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Matt Ahrens <matthew.ahrens@delphix.com>
Reviewed by: Christopher Siden <chris.siden@delphix.com>
Reviewed by: Eric Schrock <eric.schrock@delphix.com>
Reviewed by: Richard Lowe <richlowe@richlowe.net>
Reviewed by: Dan McDonald <danmcd@nexenta.com>
Approved by: Eric Schrock <eric.schrock@delphix.com>
Actions