Date: Thu, 29 Apr 2004 14:19:47 -0700
From: Andrew Morton <akpm@osdl.org>
To: Paul Jackson <pj@sgi.com>
Cc: vonbrand@inf.utfsm.cl, nickpiggin@yahoo.com.au, jgarzik@pobox.com,
       brettspamacct@fastclick.com, linux-kernel@vger.kernel.org
Subject: Re: ~500 megs cached yet 2.6.5 goes into swap hell
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In-Reply-To: <20040429133613.791f9f9b.pj@sgi.com>
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	<200404292001.i3TK1BYe005147@eeyore.valparaiso.cl>
	<20040429133613.791f9f9b.pj@sgi.com>
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Paul Jackson <pj@sgi.com> wrote:
>
> > How on earth is the kernel supposed to know that for this one particular
> > job you don't care if it takes 3 hours instead of 10 minutes,
> 
> I'd pay ten bucks (yeah, I'm a cheapskate) for an option that I could
> twiddle that would mark my nightly updatedb and backup jobs as ones to
> use reduced memory footprint (both for file caching and backing user
> virtual address space), even if it took much longer.
> 
> So, rather than protest in mock outrage that it's impossible for the
> kernel to know this, instead answer the question as stated in all
> seriousness ... well ... how _could_ the kernel know, and what _could_
> the kernel do if it knew.  What mechanism(s) would be needed so that
> the kernel could restrict a jobs memory usage?

Two things:

a) a knob to say "only reclaim pagecache".  We have that now.

b) a knob to say "reclaim vfs caches harder".  That's simply a matter of boosting
   the return value from shrink_dcache_memory() and perhaps shrink_icache_memory().

It's not quite what you're after, but it's close.
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