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Date: Mon, 16 Jul 2001 21:01:55 -0300 (BRT)
From: Marcelo Tosatti <marcelo@conectiva.com.br>
To: Kanoj Sarcar <kanojsarcar@yahoo.com>
Cc: lkml <linux-kernel@vger.kernel.org>, Rik van Riel <riel@conectiva.com.br>,
        Dirk Wetter <dirkw@rentec.com>, Mike Galbraith <mikeg@wen-online.de>,
        linux-mm@kvack.org, "Stephen C. Tweedie" <sct@redhat.com>
Subject: Re: [PATCH] Separate global/perzone inactive/free shortage 
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On Mon, 16 Jul 2001, Kanoj Sarcar wrote:

> 
> --- Marcelo Tosatti <marcelo@conectiva.com.br> wrote:
> > Hi,
> > 
> > As well known, the VM does not make a distiction
> > between global and
> > per-zone shortages when trying to free memory. That
> > means if only a given
> > memory zone is under shortage, the kernel will scan
> > pages from all zones. 
> > 
> > The following patch (against 2.4.6-ac2), changes the
> > kernel behaviour to
> > avoid freeing pages from zones which do not have an
> > inactive and/or
> > free shortage.
> > 
> > Now I'm able to run memory hogs allocating 4GB of
> > memory (on 4GB machine)
> > without getting real long hangs on my ssh session.
> > (which used to happen
> > on stock -ac2 due to exhaustion of DMA pages for
> > networking).
> > 
> > Comments ? 
> > 
> > Dirk, Can you please try the patch and tell us if it
> > fixes your problem ? 
> > 
> > 
> 
> Just a quick note. A per-zone page reclamation
> method like this was what I had advocated and sent
> patches to Linus for in the 2.3.43 time frame or so.
> I think later performance work ripped out that work.
> I guess the problem is that a lot of the different
> page reclamation schemes first of all do not know
> how to reclaim pages for a specific zone, and secondly
> have to go thru a lot of work before they discover the
> page they are trying to reclaim does not belong to the
> shortage zone, hence wasting a lot of work/cputime.
> try_to_swap_out is a good example, which can be solved
> by rmaps. 

Oh sure, rmaps would fix the performance problem caused by this. But I we
dont have rmaps right now, and I doubt we want rmaps for 2.4.

Besides, the performance degradation of doing the perzone
aging/deactivation this way is nothing compared to _not_ doing the thing
on a perzone basis at all, IMHO.

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