Re: [PATCH v2 block 1/2] writeback, cgroup: Adjust WB_FRN_TIME_CUT_DIV to accelerate foreign inode switching

[Jens Axboe]

On 8/15/19 1:25 PM, Tejun Heo wrote:
> WB_FRN_TIME_CUT_DIV is used to tell the foreign inode detection logic
> to ignore short writeback rounds to prevent getting confused by a
> burst of short writebacks.  The parameter is currently 2 meaning that
> anything smaller than half of the running average writback duration
> will be ignored.
> 
> This is unnecessarily aggressive.  The detection logic uses 16 history
> slots and is already reasonably protected against some short bursts
> confusing it and the current parameter can lead to tens of seconds of
> missed detection depending on the writeback pattern.
> 
> Let's change the parameter to 8, so that it only ignores writeback
> with are smaller than 12.5% of the current running average.
> 
> v2: Add comment explaining what's going on with the foreign detection
>      parameters.

Applied 1-2 for 5.4, thanks.

-- 
Jens Axboe