On Thu, Apr 06, 2017 at 11:22:47AM +0800, Anand Jain wrote: > As of now we do alloc an empty bio and then use the flag REQ_PREFLUSH > to flush the device cache, instead we can use blkdev_issue_flush() > for this puspose.
This would change the scheduling characteristics. Right now, the caller thread submits all bios from one thread, lets block layer do it's work, and then in the same thread wait for each of the submitted bios. In your code, the btrfs thread prepares tasks for each bio, shifts the work to the global workqueue (schedule_work) and then it's same as before. I'm concerned about using the global queue. As the bio submission jobs could get blocked by some other unrelated task queued there, the guarantees depend on the forward progress of the tasks scheduled (plus block layer processing). In the current behaviour, the guarantees stand on the block layer only. We could introduce yet another work queue and submit the bios there, with possible fine tuning of the flags, like priority or emergency etc. But that sounds like unnecessary work as we can simply keep the code as-is and get the same end result. Regarding other patches, some of them are independent so I'll see what can be merged now regardless of the above comments. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
