Re: [RFC 2/3] vmscan hook

[Rik van Riel]

On 01/18/2012 09:25 PM, KAMEZAWA Hiroyuki wrote:
> On Wed, 18 Jan 2012 09:17:17 -0500
> Rik van Riel<riel@xxxxxxxxxx>  wrote:
>
> > On 01/17/2012 07:18 PM, KAMEZAWA Hiroyuki wrote:
> > > On Wed, 18 Jan 2012 08:08:01 +0900
> > > Minchan Kim<minchan@xxxxxxxxxx>   wrote:
> > >
> > > > > > > 2. can't we measure page-in/page-out distance by recording something ?
> > > > > >
> > > > > > I can't understand your point. What's relation does it with swapout prevent?
> > > > >
> > > > > If distance between pageout ->   pagein is short, it means thrashing.
> > > > > For example, recoding the timestamp when the page(mapping, index) was
> > > > > paged-out, and check it at page-in.
> > > >
> > > > Our goal is prevent swapout. When we found thrashing, it's too late.
> > >
> > > If you want to prevent swap-out, don't swapon any. That's all.
> > > Then, you can check the number of FILE_CACHE and have threshold.
> >
> > I think you are getting hung up on a word here.
> >
> > As I understand it, the goal is to push out the point where
> > we start doing heavier swap IO, allowing us to overcommit
> > memory more heavily before things start really slowing down.
>
> Yes.
>
> Hmm, considering that the issue is slow down,
>
> time values as
>
> - 'cpu time used for memory reclaim'
> - 'latency of page allocation'
> - 'application execution speed' ?
>
> may be a better score to see rather than just seeing lru's stat.

I believe those all qualify as "too late".

We want to prevent things from becoming bad, for as long
as we (easily) can.

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