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SubjectRe: [PATCH 0/3] VM throttling: avoid blocking occasional writers
Tomoki Sekiyama wrote:
> Hi,
>
> Thanks for your comments.
> I'm sorry for my late reply.
>
> Bill Davidsen wrote:
> > Andrew Morton wrote:
>
> >> - I wonder if dirty_limit_ratio is the best name we could choose.
> >> vm_dirty_blocking_ratio, perhaps? Dunno.
> >>
> > I don't like it, but I dislike it less than "dirty_limit_ratio" I
> guess.
> > It would probably break things to change it now, including my
> > sysctl.conf on a number of systems :-(
>
> I'm wondering which interface is preferred...
>
> 1) Just rename "dirty_limit_ratio" to "dirty_blocking_ratio."
> Those who had been changing dirty_ratio should additionally modify
> dirty_blocking_ratio in order to determine the upper limit of dirty
> pages.
>
> 2) Change "dirty_ratio" to a vector, consists of 2 values;
> {blocking ratio, writeback starting ratio}.
> For example, to change the both values:
> # echo 40 35 > /proc/sys/vm/dirty_ratio
> And to change only the first one:
> # echo 20 > /proc/sys/vm/dirty_ratio
> In the latter way the writeback starting ratio is regarded as the
> same as the
> blocking ratio if the writeback starting ratio is smaller. And
> then, the kernel behaves
> similarly as the current kernel.
>
> 3) Use "dirty_ratio" as the blocking ratio. And add
> "start_writeback_ratio", and start writeback at
> start_writeback_ratio(default:90) * dirty_ratio / 100 [%].
> In this way, specifying blocking ratio can be done in the same way as
> current kernel, but high/low watermark algorithm is enabled.
I like 3 better, it should make tuning behavior more precise. You can
make an argument for absolute values for writeback, if my disk will only
write 70MB/s I may only want 203 sec of pending writes, regardless of
available memory.

--
bill davidsen <davidsen@tmr.com>
CTO TMR Associates, Inc
Doing interesting things with small computers since 1979

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