Re: [PATCH] remove compaction from kswapd

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 2 Mar 2011 08:10:35 +0900
Minchan Kim <minchan.kim@gmail.com> wrote:

> On Wed, Mar 2, 2011 at 7:39 AM, Andrea Arcangeli <aarcange@redhat.com> wrote:
> > On Wed, Mar 02, 2011 at 07:33:13AM +0900, Minchan Kim wrote:
> >> Sorry for bothering you but I think you get the data.
> >> It helps someone in future very much to know why we determined to
> >> remove the feature at that time and they should do what kinds of
> >> experiment to prove it has a benefit to add compaction in kswapd
> >> again.
> >
> > This is a benchmark I'm unsure if it's ok to publish results but it
> > should be possible to simulate it with a device driver.
> >
> > Arthur provided kswapd load usage data too, so I hope that's enough.
> >
> > My other patch (compaction-kswapd-3) is way better than current logic
> > and retains compaction in kswapd. That shows slightly higher
> > kswapd utilization with Arthur's multimedia workload, and a bit worse
> > performance on the network benchmark. So I thought it was better to go
> > with the fastest potion as long as we don't have a logic that uses
> > compaction and shows improved performance and lower latency than with
> > no compaction at all in kswapd.
> >
> 
> I didn't notice Arthur's problem.
> The patch seems to fix a real problem so I think it's enough.
> I wished you wrote down the link url about Arthur on LKML.
> 
> You can remove compact_mode of compact_control.
> Otherwise, looks good to me.
> 

I'd be pretty worried about jamming this into 2.6.38 at this late
stage.  And some vague talk about something Arthur did really doesn't
help a lot!  It would be better to have some good, solid quantitative
justification for what is really an emergency patch.  

Bear in mind that we always have a middle option: merge a patch into
2.6.39-rc1 and tag it for backporting into 2.6.38.x.  That gives us
more time to test it and to generally give it a shakedown.  But to make
decisions like that and to commend a patch to the -stable maintainers,
we need to provide better information please.

Also, "This goes on top of the two lowlatency fixes for compaction"
isn't particularly helpful.  I need to verify that the referred-to
patches are already in mainline but I don't have a clue what this
description refers to.  More specificity, please - it helps avoid
mistakes.

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