ZFS txg implementation flaw

[Allan Jude]

On 2013-10-28 14:25, aurfalien wrote:
> On Oct 28, 2013, at 11:16 AM, Slawa Olhovchenkov wrote:
>
>> On Mon, Oct 28, 2013 at 10:45:02AM -0700, aurfalien wrote:
>>
>>> On Oct 28, 2013, at 2:28 AM, Slawa Olhovchenkov wrote:
>>>
>>>> I can be wrong.
>>>> 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.
>>>>
>>>> In systat -vmstat I see totfr up to 600000, prcfr up to 200000.
>>>>
>>>> Estimated overhead -- 30% of system time.
>>>>
>>>> Can anybody implement thread and page pool for txg?
>>> Would lowering vfs.zfs.txg.timeout be a way to tame or mitigate this?
>> vfs.zfs.txg.timeout: 5
>>
>> Only x5 lowering (less in real case with burst writing). And more fragmentation on writing and etc.
> So leave it default in other words.
>
> Good to know.
>
> - aurf
>
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The default is the default for a reason, although the original default
was 30

-- 
Allan Jude