linux-kernel - Re: [PATCH] vmscan: prevent background aging of anon page in no swap system

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Date:	Tue, 31 Aug 2010 10:38:10 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com, Ying Han <yinghan@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Venkatesh Pallipadi <venki@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH] vmscan: prevent background aging of anon page in no swap system

> > I think both Ying's and Minchan's opnion are right and makes sense.  however I _personally_
> > like Ying version because 1) this version is simpler 2) swap full is very rarely event 3)
> > no swap mounting is very common on HPC. so this version could have a chance to
> > improvement hpc workload too.
> 
> I agree.
> 
> >
> > In the other word, both avoiding unnecessary TLB flush and keeping proper page aging are
> > performance matter. so when we are talking performance, we always need to think frequency
> > of the event.
> 
> Ying's one and mine both has a same effect.
> Only difference happens swap is full. My version maintains old
> behavior but Ying's one changes the behavior. I admit swap full is
> rare event but I hoped not changed old behavior if we doesn't find any
> problem.
> If kswapd does aging when swap full happens, is it a problem?
> We have been used to it from 2.6.28.
> 
> If we regard a code consistency is more important than _unexpected_
> result, Okay. I don't mind it. :)

To be honest, I don't mind the difference between you and Ying's version. because
_practically_ swap full occur mean the application has a bug. so, proper page aging
doesn't help so much. That's the reason why I said I prefer simper. I don't have 
strong opinion. I think it's not big matter.


> But at least we should do more thing to make the patch to compile out
> for non-swap configurable system.

Yes, It makes embedded happy :)



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