On Fri, Aug 19, 2011 at 07:55:43PM +0800, Artem Bityutskiy wrote:

On Thu, 2011-08-18 at 21:13 +0800, Wu Fengguang wrote:

quoted

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.

OK, thanks for the information. What do you mean by "not have this
problem any more"? Did you worked around it in other ways, such as
sync mount (which seems rather inefficient though)?

Thanks,
Fengguang

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