Date: Tue, 9 Nov 2004 08:42:21 -0200
From: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
To: Andrew Morton <akpm@osdl.org>
Cc: Chuck Ebbert <76306.1226@compuserve.com>, linux-kernel@vger.kernel.org,
       nickpiggin@yahoo.com.au
Subject: Re: balance_pgdat(): where is total_scanned ever updated?
Message-ID: <20041109104220.GB6326@logos.cnet>
References: <200411061418_MC3-1-8E17-8B6C@compuserve.com> <20041106161114.1cbb512b.akpm@osdl.org>
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On Sat, Nov 06, 2004 at 04:11:14PM -0800, Andrew Morton wrote:
> Chuck Ebbert <76306.1226@compuserve.com> wrote:
> >
> > Kernel version is 2.6.9, but I see no updates to this function in BK-current.
> > How is total_scanned ever updated?  AFAICT it is always zero.
> 
> It's a bug which was introduced months ago when we added struct
> reclaim_state.
> 
> > In mm/vmscan.c:balance_pgdat(), there are these references to total_scanned
> > (missing whitepace indicated by "^"):
> > 
> > 
> >  977:        int total_scanned, total_reclaimed;
> > 
> >  983:        total_scanned = 0;
> > 
> > 1076:                        if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
> > 1077:                            total_scanned > total_reclaimed+total_reclaimed/2)
> >                                                                ^ ^             ^ ^
> > 
> > 1088:                if (total_scanned && priority < DEF_PRIORITY - 2)
> > 
> > 
> > Could this be part of the problems with reclaim?  Or have I missed something?
> 
> I had a patch which fixes it in -mm for a while.  It does increase the
> number of pages which are reclaimed via direct reclaim and decreases the
> number of pages which are reclaimed by kswapd.  As one would expect from
> throttling kswapd.  This seems undesirable.

Hi Andrew,

Do you have any numbers to backup the claim "It does increase the
number of pages which are reclaimed via direct reclaim and decreases the
number of pages which are reclaimed by kswapd", please?

Because linux-2.6.10-rc1-mm2 (and 2.6.9) completly ignores sc->may_writepage 
under normal operation, its only used when laptop_mode is on:

		if (laptop_mode && !sc->may_writepage)
			goto keep_locked;

Is this intentional ???

> I'm leaving this alone until it can be demonstrated that fixing it improves
> kernel behaviour in some manner.

I dont see it working at all?

I'll see if I find time to do some tests.. (my usual disclaimer).
-
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