Re: checkpointer continuous flushing

Fabien,

On 2015-06-03 PM 02:53, Fabien COELHO wrote:
> 
>>
>> It seems 'sync' gets closer to what I really wanted 'flush' to mean. If I
>> understand this and the previous discussion(s) correctly, the patch tries to
>> alleviate the problems caused by one-big-sync-at-the end-of-writes by doing
>> the sync in step with writes (which do abide by the
>> checkpoint_completion_target). Given that impression, it seems
>> *_sync_on_write may even do the job.
> 
> I desagree with this one, because the sync is only *initiated*, not done. For
> this reason I think that "flush" seems a better word. I understand "sync" as
> "committed to disk". For the data to be synced, it should call with the "wait
> after" option, which is a partial "fsync", but that would be terrible for
> performance as all checkpointed pages would be written one by one, without any
> opportunity for reordering them.
> 
> For what it's worth and for the record, Linux sync_file_range documentation
> says "This is an asynchronous flush-to-disk operation" to describe the
> corresponding option. This is probably where I took it.
> 

Ah, okay! I didn't quite think about the async aspect here. But, I sure do
hope that the added mechanism turns out to be *less* async than kernel's own
dirty cache handling to achieve the hoped for gain.

> So two contenders:
> 
>   *_flush_to_disk
>   *_flush_on_write
> 

Yep!

Regards,
Amit