Re: [PATCH 2/2] writeback: Adding pages_dirtied and pages_entered_writeback
From: KOSAKI Motohiro
Date: Thu Aug 05 2010 - 20:45:04 EST
> On Fri, 6 Aug 2010 09:18:59 +0900 (JST)
> KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> wrote:
> > > On Thu, Aug 5, 2010 at 4:56 PM, KOSAKI Motohiro
> > > <kosaki.motohiro@xxxxxxxxxxxxxx> wrote:
> > > > /proc/vmstat already have both.
> > > >
> > > > cat /proc/vmstat |grep nr_dirty
> > > > cat /proc/vmstat |grep nr_writeback
> > > >
> > > > Also, /sys/devices/system/node/node0/meminfo show per-node stat.
> > > >
> > > > Perhaps, I'm missing your point.
> > >
> > > These only show the number of dirty pages present in the system at the
> > > point they are queried.
> > > The counter I am trying to add are increasing over time. They allow
> > > developers to see rates of pages being dirtied and entering writeback.
> > > Which is very helpful.
> > Usually administrators get the data two times and subtract them. Isn't it sufficient?
> Nope. The existing nr_dirty is "number of pages dirtied since boot"
> minus "number of pages cleaned since boot". If you do the
> wait-one-second-then-subtract thing on nr_dirty, the result is
> dirtying-bandwidth minus cleaning-bandwidth, and can't be used to
> determine dirtying-bandwidth.
Technically, yes. I meant, _now_, typical administrators are using the
Do you mean this is wrong? or do you mean you have another use case?
> I can see that a graph of dirtying events versus time could be an
> interesting thing. I don't see how it could be obtained using the
> existing instrumentation. tracepoints, probably..
I think it depend on frequency of the usecase. If the usecase is enouth
major, convenience way (e.g. /proc/vmstat) is very helpful.
probably, I haven't understand the usecase of this feature.
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