Re: [PATCH 0/5] Some vmevent fixes...

[KOSAKI Motohiro]

(6/5/12 4:16 AM), leonid.moiseichuk@xxxxxxxxx wrote:
> > -----Original Message-----
> > From: penberg@xxxxxxxxx [mailto:penberg@xxxxxxxxx] On Behalf Of ext
> > Pekka Enberg
> > Sent: 05 June, 2012 11:02
> > To: Minchan Kim
> ...
> > > Next concern is that periodic timer of implementation.
> > > I think it would add direct hook in vmscan.c rather than peeking raw
> > > vmstat periodically by timer so we can control more fine-grained way
> > without unnecessary overhead.
> >
> > If the hooks are clean and it doesn't hurt the  !CONFIG_VMEVENT case, I'm
> > completely OK with that.
>
> On the previous iteration hooking vm was pointed as very bad idea, so in my version I installed shrinker to handle cases when we have memory pressure.
> Using deferred timer with adequate timeout (0.250 ms or larger) fully suitable for userspace and produce adequate overhead
> ->  by nature such API should not be 100% accurate, anyhow applications cannot handle situation as good as kernel can provide, 0.5MB space accuracy, 100ms is maximum user-space require for 64-1024MB devices.

I believe that's bad idea. In fact, An "adequate" timeout depend on hardware, not application performance tendency. Thus, applications can't know "adequate" value.

 
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