Date: Mon, 28 Oct 2013 14:56:17 -0700 From: Xin Li <delphij@delphij.net> To: Slawa Olhovchenkov <slw@zxy.spb.ru>, d@delphij.net Cc: freebsd-fs@freebsd.org, freebsd-current@freebsd.org, Jordan Hubbard <jkh@ixsystems.com> Subject: Re: ZFS txg implementation flaw Message-ID: <526EDD81.8000109@delphij.net> In-Reply-To: <20131028214552.GY63359@zxy.spb.ru> References: <20131028092844.GA24997@zxy.spb.ru> <9A00B135-7D28-47EB-ADB3-E87C38BAC6B6@ixsystems.com> <20131028213204.GX63359@zxy.spb.ru> <526ED956.10202@delphij.net> <20131028214552.GY63359@zxy.spb.ru>
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On 10/28/13 14:45, Slawa Olhovchenkov wrote:
> On Mon, Oct 28, 2013 at 02:38:30PM -0700, Xin Li wrote:
>
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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@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
>
> 0xffffffff80cdbfd0 <fork_trampoline>: mov %r12,%rdi
> 0xffffffff80cdbfd3 <fork_trampoline+3>: mov %rbx,%rsi
> 0xffffffff80cdbfd6 <fork_trampoline+6>: mov %rsp,%rdx
> 0xffffffff80cdbfd9 <fork_trampoline+9>: callq 0xffffffff808db560
> <fork_exit> 0xffffffff80cdbfde <fork_trampoline+14>: jmpq
> 0xffffffff80cdca80 <doreti> 0xffffffff80cdbfe3
> <fork_trampoline+19>: nopw 0x0(%rax,%rax,1)
> 0xffffffff80cdbfe9 <fork_trampoline+25>: nopl 0x0(%rax)
>
>
>>> 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?
>
> kern.maxvnodes: 1095872 kern.minvnodes: 273968
> vm.stats.vm.v_vnodepgsout: 0 vm.stats.vm.v_vnodepgsin: 62399
> vm.stats.vm.v_vnodeout: 0 vm.stats.vm.v_vnodein: 10680
> vfs.freevnodes: 275107 vfs.wantfreevnodes: 273968 vfs.numvnodes:
> 316321 debug.sizeof.vnode: 504
Try setting vfs.wantfreevnodes to 547936 (double it).
Cheers,
- --
Xin LI <delphij@delphij.net> https://www.delphij.net/
FreeBSD - The Power to Serve! Live free or die
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