Re: [PATCH 0/3] VM throttling: avoid blocking occasional writers

[Bill Davidsen <davidsen@tmr.com>]

Tomoki Sekiyama wrote:
> Hi,
> Thanks for your reply.
>
>   
>>> 3) Use "dirty_ratio" as the blocking ratio. And add
>>>   "start_writeback_ratio", and start writeback at
>>>   start_writeback_ratio(default:90) * dirty_ratio / 100 [%].
>>>   In this way, specifying blocking ratio can be done in the same way
>>>   as current kernel, but high/low watermark algorithm is enabled.
>>>       
>> I like 3 better, it should make tuning behavior more precise.
>>     
>
> Then, what do you think of the following idea?
>
> (4) add `dirty_start_writeback_ratio' as percentage of memory,
>     at which a generator of dirty pages itself starts writeback
>     (that is, non-blocking ratio).
>
> In this way, `dirty_ratio' is used as the blocking ratio, so we don't
> need to modify the sysctl.conf etc. I think it's easier to understand
> for administrators of systems, because the interface is similar as
> `dirty_background_ratio' and`dirty_ratio.'
>
> If this is OK, I'll repost the patch.
>   
It sounds good to me, just be sure behavior is sane for for both 
blocking less than start_writeback and vice versa.
>   
>> You can make an argument for absolute values for writeback,
>> if my disk will only write 70MB/s I may only want 203 sec of
>> pending writes, regardless of available memory.
>>     
>
> To realize tuning with absolute values, I consider that we need to
> modify handling of `dirty_background_ratio,' `dirty_ratio' and so on as
> well as `dirty_start_writeback_ratio.' I think this should be done in
> another patch if this feature is required.
>
> Regards,
> --
> Tomoki Sekiyama
> Hitachi, Ltd., Systems Development Laboratory
>
>
>   


-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979