ZFS txg implementation flaw

[Xin Li]

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On 10/28/13 14:32, Slawa Olhovchenkov wrote:
> On Mon, Oct 28, 2013 at 02:22:16PM -0700, Jordan Hubbard wrote:
> 
>> 
>> On Oct 28, 2013, at 2:28 AM, Slawa Olhovchenkov <slw at zxy.spb.ru>
>> wrote:
>> 
>>> As I see ZFS cretate seperate thread for earch txg writing. 
>>> Also for writing to L2ARC. As result -- up to several thousands
>>> threads created and destoyed per second. And hundreds thousands
>>> page allocations, zeroing, maping unmaping and freeing per
>>> seconds. Very high overhead.
>> 
>> How are you measuring the number of threads being created /
>> destroyed?   This claim seems erroneous given how the ZFS thread
>> pool mechanism actually works (and yes, there are thread pools
>> already).
>> 
>> It would be helpful to both see your measurement methodology and
>> the workload you are using in your tests.
> 
> Semi-indirect. dtrace -n 'fbt:kernel:vm_object_terminate:entry {
> @traces[stack()] = count(); }'
> 
> After some (2-3) seconds
> 
> kernel`vnode_destroy_vobject+0xb9 zfs.ko`zfs_freebsd_reclaim+0x2e 
> kernel`VOP_RECLAIM_APV+0x78 kernel`vgonel+0x134 
> kernel`vnlru_free+0x362 kernel`vnlru_proc+0x61e 
> kernel`fork_exit+0x11f kernel`0xffffffff80cdbfde 2490
> 
> I don't have user process created threads nor do fork/exit.

This has nothing to do with fork/exit but does suggest that you are
running of vnodes.  What does sysctl -a | grep vnode say?

Cheers,
- -- 
Xin LI <delphij at delphij.net>    https://www.delphij.net/
FreeBSD - The Power to Serve!           Live free or die
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