linux-kernel - Re: [RFC PATCH 0/3] Avoid the use of congestion

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Message-ID: <20100421090327.GD5336@cmpxchg.org>
Date:	Wed, 21 Apr 2010 11:03:27 +0200
From:	Johannes Weiner <hannes@...xchg.org>
To:	Christian Ehrhardt <ehrhardt@...ux.vnet.ibm.com>
Cc:	Rik van Riel <riel@...hat.com>, Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	Nick Piggin <npiggin@...e.de>,
	Chris Mason <chris.mason@...cle.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	linux-kernel@...r.kernel.org, gregkh@...ell.com,
	Corrado Zoccolo <czoccolo@...il.com>
Subject: Re: [RFC PATCH 0/3] Avoid the use of congestion_wait under zone pressure

On Wed, Apr 21, 2010 at 06:23:45AM +0200, Christian Ehrhardt wrote:
> Rik van Riel wrote:
> >You do not want the backup to kick the working set
> >out of memory, because when the user returns in the
> >morning the desktop should come back quickly after
> >the screensaver is unlocked.
> 
> IMHO it is fine to prevent that nightly backup job from not being 
> finished when the user arrives at morning because we didn't give him 
> some more cache - and e.g. a 30 sec transition from/to both optimized 
> states is fine.

For batched work maybe :-)

> What we could do is combine all our thoughts we had so far:
> a) Rik could create an experimental patch that excludes the in flight pages
> b) Johannes could create one for his suggestion to "always scan active 
> file pages but only deactivate them when the ratio is off and otherwise 
> strip buffers of clean pages"

Please drop that idea, that 'Buffers:' is a red herring.  It's just pages
that do not back files but block devices.  Stripping buffer_heads won't
achieve anything, we need to get rid of the pages.  Sorry, I should have
slept and thought before writing that suggestion.
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