Re: [PATCH v2 3/3] generic/470: add syncfs test

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> 
> 在 2017年12月11日,下午6:46,Amir Goldstein <amir73il@xxxxxxxxx> 写道:
> 
> On Mon, Dec 11, 2017 at 12:03 PM, Chengguang Xu <cgxu519@xxxxxxxxxx> wrote:
>>> 
>>> 在 2017年12月7日,下午4:17,Amir Goldstein <amir73il@xxxxxxxxx> 写道:
> [...]
>> 
>> I did more detail tests for three different data modes of ext4 and found
>> the overlayfs syncfs bug is reproducible on data=ordered and data=writeback,
>> but on data=journal mode, data is flushed and correct.
> 
> That is expected, because overlayfs does call upper's sync_fs() method and
> for journal=data that will flush all dirty pages as well.
> 
>> I only wrote only a few words
>> to a single file and the bug is always reproducible on my test environment.
>> 
>> For writeback interferences, AFAIK, from dirty ratio and period.
>> If we drop all dirty caches & sync before the test, I think we can
>> avoid interference from it.
>> 
> 
> Why? does either drop_caches or sync() reset the flusher thread
> periodic flush dirty pages?

Sorry,We have to finish test in 30 seconds after we write test file, 
otherwise may be affected by background flusher. 


> 
>> So if we don’t have anything else to interference test result,
>> I just want to modify to write a small single file as test target.
>> 
>> Am I missing anything?
> 
> I think the chance of flusher thread interfering the test and
> flushing the dirty page you wrote before _scratch_shutdown exists,
> but is small enough so we can neglect it and keep the test as simple
> as possible.

As I know, in normal case flusher thread check dirty inode expiring every 5 seconds(default) and flush dirty 
inode when expires 30 seconds(default). If we can finish test in 30s after running test, it would be OK. 
What do you think? 


> 
> Amir.

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