Messages in this thread | | | Date | Mon, 21 Nov 2011 19:35:40 +0800 | From | Wu Fengguang <> | Subject | Re: [PATCH 2/8] readahead: make default readahead size a kernel parameter |
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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@suse.de> > > > > 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.
Thanks, Fengguang
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