Re: [PATCH] writeback: Per-block device bdi->dirty_writeback_interval and bdi->dirty_expire_interval.

[Artem Bityutskiy <dedekind1@gmail.com>]

On Thu, 2011-08-18 at 21:13 +0800, Wu Fengguang wrote:
> Thinking twice about it, I find that the different requirements for
> interval flash/external microSD can also be solved by this scheme.
> 
> Introduce a per-bdi dirty_background_time (and optionally dirty_time)
> as the counterpart of (and works in parallel to) global dirty[_background]_ratio,
> however with unit "milliseconds worth of data".
> 
> The per-bdi dirty_background_time will be set low for external microSD
> and high for internal flash. Then you get timely writeouts for microSD
> and reasonably delayed writes for internal flash (controllable by the
> global dirty_expire_centisecs).
> 
> The dirty_background_time will actually work more reliable than
> dirty_expire_centisecs because it will checked immediately after the
> application dirties more pages. And the dirty_time could provide
> strong data integrity guarantee -- much stronger than
> dirty_expire_centisecs -- if used.
> 
> Does that sound reasonable?

Yes, this would probably work. But note, we do not have this problem
anymore, I was just talking about the past experience, so I cannot
validate any possible patch.

Thanks.

-- 
Best Regards,
Artem Bityutskiy