On Sat, 2009-09-05 at 14:26 +0100, Jamie Lokier wrote: > Richard Kennedy wrote: > > I've been testing this & it works pretty well here, but setting > > max_writeback_mb to 128 seems much too large for normal desktop machines. > > > > Because it is so large the background writes don't stop when they get > > down to the background threshold, but just keep on writing. > > background_threshold on my machine is only about 300Mb so it can > > undershoot by quite a bit. This could impact random write workloads > > significantly. > > If that's true, would it be even worse for embedded devices with, say, > just 32MB RAM? It sounds like writeback undershoot might be rather > extreme in that case. Well, on a machine that small I don't think it will be any worse. The current code tries to write 1024 pages so its undershoot will be about 100% anyway. > Also on this topic, should max_writeback be smaller for slow disks? I > have a small device here with a hard disk that can only be written at > 2-10MB/s due to limitations of the built-in IDE controller. > > I know that's unusual, but it shows there is quite a wide range of > speeds at which disks can be written, even just counting hard disks. > > -- Jamie I'm not sure about that, it will depend on how the background threshold issue gets fixed. regards Richard -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
