Hi Wu, On Thu, Aug 18, 2011 at 6:43 PM, Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote: > Hi Artem, > >> Here is a real use-case we had when developing the N900 phone. We had >> internal flash and external microSD slot. Internal flash is soldered in >> and cannot be removed by the user. MicroSD, in contrast, can be removed >> by the user. >> >> For the internal flash we wanted long intervals and relaxed limits to >> gain better performance. >> >> For MicroSD we wanted very short intervals and tough limits to make sure >> that if the user suddenly removes his microSD (users do this all the >> time) - we do not lose data. > > 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? > > Thanks, > Fengguang > My understanding of your email appears that you are agreeing in principle that the temporal aspect of this problem needs to be addressed along with your spatial pattern analysis technique. I feel a more generic solution to the problem is required because the problem faced by Artem can appear in a different situation for a different application. I can re-implement my original patch in either centiseconds or milliseconds as suggested by you. Kindly advise if my understanding is correct. Thanks, Kautuk Consul. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>