On Fri, Nov 25, 2011 at 08:36:33AM +0800, Dave Chinner wrote: > On Thu, Nov 24, 2011 at 11:28:22PM +0100, Jan Kara wrote: > > On Mon 21-11-11 19:35:40, Wu Fengguang wrote: > > > On Mon, Nov 21, 2011 at 06:01:37PM +0800, Christoph Hellwig wrote: > > > > On Mon, Nov 21, 2011 at 05:18:21PM +0800, Wu Fengguang wrote: > > > > > From: Nikanth Karthikesan <knikanth@xxxxxxx> > > > > > > > > > > Add new kernel parameter "readahead=", which allows user to override > > > > > the static VM_MAX_READAHEAD=128kb. > > > > > > > > Is a boot-time paramter really such a good idea? I would at least > > > > > > It's most convenient to set at boot time, because the default size > > > will be used to initialize all the block devices. > > > > > > > make it a sysctl so that it's run-time controllable, including > > > > beeing able to set it from initscripts. > > > > > > Once boot up, it's more natural to set the size one by one, for > > > example > > > > > > blockdev --setra 1024 /dev/sda2 > > > or > > > echo 512 > /sys/block/sda/queue/read_ahead_kb > > > > > > And you still have the chance to modify the global default, but the > > > change will only be inherited by newly created devices thereafter: > > > > > > echo 512 > /sys/devices/virtual/bdi/default/read_ahead_kb > > > > > > The above command is very suitable for use in initscripts. However > > > there are no natural way to do sysctl as there is no such a global > > > value. > > Well, you can always have an udev rule to set read_ahead_kb to whatever > > you want. In some respect that looks like a nicer solution to me... > > And one that has already been in use for exactly this purpose for > years. Indeed, it's far more flexible because you can give different > types of devices different default readahead settings quite easily, > and it you can set different defaults for just about any tunable > parameter (e.g. readahead, ctq depth, max IO sizes, etc) in the same > way. I'm interested in this usage, too. Would you share some of your rules? > Hence I don't think we should treat default readahead any > differently from any other configurable storage parameter - we've > already got places to change the per-device defaults to something > sensible at boot/discovery time.... OK, I'll drop this patch. Thanks, Fengguang -- 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>