Hi Chen,
thanks for the update. Will prepare patch to periodically reset
StupidAllocator today.
And just to let you know below is an e-mail from AdamK from RH which
might explain the issue with the allocator.
Also please note that StupidAllocator might not perform full
defragmentation in run-time. That's why we observed (mentioned somewhere
in the thread) fragmentation growth while OSD is running and its drop on
restart. Such a restart rebuilds internal tree and eliminates
defragmentation flaws. May be that's the case.
Thanks,
Igor
-------- Forwarded Message --------
Subject: High CPU in StupidAllocator
Date: Tue, 12 Feb 2019 10:24:37 +0100
From: Adam Kupczyk <akupczyk@xxxxxxxxxx>
To: IGOR FEDOTOV <ifed75@xxxxxxxxx>
Hi Igor,
I have observed that StupidAllocator can burn a lot of CPU in
StupidAllocator::allocate_int().
This comes from loops:
while (p != free[bin].end()) {
if (_aligned_len(p, alloc_unit) >= want_size) {
goto found;
}
++p;
}
It happens when want_size is close to limit of size of bin.
For example, free[5] contains sizes 8192..16383.
When requesting size like 16000 it is quite likely that multiple chunks
must be checked.
I have made an attempt to improve it by increasing amount of buckets.
It is done in aclamk/wip-bs-stupid-allocator-2 .
Best regards,
Adam Kupczyk
On 3/1/2019 11:46 AM, Xiaoxi Chen wrote:
igor，
I can test the patch if we have a package.
My enviroment and workload can consistently reproduce the latency
2-3 days after restarting.
Sage tells me to try bitmap allocator to make sure stupid
allocator is the bad guy. I have some osds in luminous +bitmap and
some osds in 14.1.0+bitmap. Both looks positive till now, but i need
more time to be sure.
The perf ,log and admin socket analysis lead to the theory that
in alloc_int the loop sometimes take long time wkth allocator locks
held. Which blocks release part called from _txc_finish in
kv_finalize_thread, this thread is also the one to calculate
state_kv_committing_lat and overall commit_lat. You can find from
admin socket that state_done_latency has similar trend as commit_latency.
But we cannot find a theory to.explain why reboot helps, the
allocator btree will be rebuild from freelist manager and.it.should be
exactly. the same as it is prior to reboot. Anything related with pg
recovery?
Anyway, as I have a live env and workload, I am more than willing
to work with you for further investigatiom
-Xiaoxi
Igor Fedotov <ifedotov@xxxxxxx <mailto:ifedotov@xxxxxxx>> 于
2019年3月1日周五 上午6:21写道：
Also I think it makes sense to create a ticket at this point. Any
volunteers?
On 3/1/2019 1:00 AM, Igor Fedotov wrote:
> Wondering if somebody would be able to apply simple patch that
> periodically resets StupidAllocator?
>
> Just to verify/disprove the hypothesis it's allocator relateted
>
> On 2/28/2019 11:57 PM, Stefan Kooman wrote:
>> Quoting Wido den Hollander (wido@xxxxxxxx <mailto:wido@xxxxxxxx>):
>>> Just wanted to chime in, I've seen this with
Luminous+BlueStore+NVMe
>>> OSDs as well. Over time their latency increased until we
started to
>>> notice I/O-wait inside VMs.
>> On a Luminous 12.2.8 cluster with only SSDs we also hit this
issue I
>> guess. After restarting the OSD servers the latency would drop
to normal
>> values again. See https://owncloud.kooman.org/s/BpkUc7YM79vhcDj
>>
>> Reboots were finished at ~ 19:00.
>>
>> Gr. Stefan
>>
