Andreas Dilger wrote: > On Dec 22, 2008 14:15 -0500, Ric Wheeler wrote: >> Without having dived into the patch in detail, one worry I would have is >> that we still might care to spin up a drive for empty transactions in >> order to invalidate the drive's write cache. >> >> For example, if we have the following sequence: >> >> (1) user app performs series of writes to file A >> (2) pages dirtied from writes to A are destaged to the disk over time >> (3) user app issues fsync(file A) to make sure that the data will >> survive a power outage >> >> At this point in time, would this change prevent us from spinning up the >> drive and invalidating the disk write cache for that fsync() ? > > Well, if the writes themselves didn't spin up the drive, it is uncertain > whether the write of the journal commit block would be any more helpful > in getting that to happen. So, ext4_sync_file() calls blkdev_issue_flush() which would should do the right thing even if the drive is spun down, I think (rather than hoping that some other journal activity would flush this out...) I guess I don't know for sure what blkdev_issue_flush does on a spun-down drive but I'd hope it does the right thing. Pretty sure I sent a patch for ext3 to do the same, but it was ignored/dropped/forgotten along with the barriers-by-default patch. Suppose I could try again. -Eric -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
