> writeback: remove the internal 5% low bound on dirty_ratio
>
> The dirty_ratio was silently limited in global_dirty_limits() to >= 5%. This
> is not a user expected behavior. And it's inconsistent with calc_period_shift(),
> which uses the plain vm_dirty_ratio value. So let's rip the internal bound.
>
> At the same time, force a user visible low bound of 1% for the vm.dirty_ratio
> interface. Applications trying to write 0 will be rejected with -EINVAL. This
> will break user space applications if they
> 1) try to write 0 to vm.dirty_ratio
> 2) and check the return value
> That is very weird combination, so the risk of breaking user space is low.
I'm ok this one too. because I bet nobody use 0% dirty ratio on their production
server and/or their own desktop. (i.e. I don't mind lab machine crash)
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
>
> CC: Jan Kara <jack@xxxxxxx>
> CC: Neil Brown <neilb@xxxxxxx>
> CC: Rik van Riel <riel@xxxxxxxxxx>
> CC: Con Kolivas <kernel@xxxxxxxxxxx>
> CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> CC: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
> ---
> kernel/sysctl.c | 2 +-
> mm/page-writeback.c | 10 ++--------
> 2 files changed, 3 insertions(+), 9 deletions(-)
>
> --- linux-next.orig/mm/page-writeback.c 2010-08-20 20:14:11.000000000 +0800
> +++ linux-next/mm/page-writeback.c 2010-08-23 10:31:01.000000000 +0800
> @@ -415,14 +415,8 @@ void global_dirty_limits(unsigned long *
>
> if (vm_dirty_bytes)
> dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
> - else {
> - int dirty_ratio;
> -
> - dirty_ratio = vm_dirty_ratio;
> - if (dirty_ratio < 5)
> - dirty_ratio = 5;
> - dirty = (dirty_ratio * available_memory) / 100;
> - }
> + else
> + dirty = (vm_dirty_ratio * available_memory) / 100;
>
> if (dirty_background_bytes)
> background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
> --- linux-next.orig/kernel/sysctl.c 2010-08-23 14:06:11.000000000 +0800
> +++ linux-next/kernel/sysctl.c 2010-08-23 14:07:30.000000000 +0800
> @@ -1029,7 +1029,7 @@ static struct ctl_table vm_table[] = {
> .maxlen = sizeof(vm_dirty_ratio),
> .mode = 0644,
> .proc_handler = dirty_ratio_handler,
> - .extra1 = &zero,
> + .extra1 = &one,
> .extra2 = &one_hundred,
> },
> {
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