Re: [RFC PATCH 0/3] Avoid the use of congestion_wait under zone pressure

[Johannes Weiner <hannes@cmpxchg.org>]

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.