linux-kernel - Re: -mm merge plans for 2.6.23

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Message-ID: <20070728002403.GK11166@waste.org>
Date:	Fri, 27 Jul 2007 19:24:03 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ray Lee <ray-lk@...rabbit.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Eric St-Laurent <ericstl34@...patico.ca>,
	Rene Herman <rene.herman@...il.com>,
	Jesper Juhl <jesper.juhl@...il.com>,
	ck list <ck@....kolivas.org>, Ingo Molnar <mingo@...e.hu>,
	Paul Jackson <pj@....com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: -mm merge plans for 2.6.23

On Wed, Jul 25, 2007 at 11:50:37PM -0700, Andrew Morton wrote:
> On Wed, 25 Jul 2007 23:33:24 -0700 "Ray Lee" <ray-lk@...rabbit.org> wrote:
> 
> > > So.  We can
> > >
> > > a) provide a way for userspace to reload pagecache and
> > >
> > > b) merge maps2 (once it's finished) (pokes mpm)
> > >
> > > and we're done?
> > 
> > Eh, dunno. Maybe?
> > 
> > We're assuming we come up with an API for userspace to get
> > notifications of evictions (without polling, though poll() would be
> > fine -- you know what I mean), and an API for re-victing those things
> > on demand.
> 
> I was assuming that polling would work OK.  I expect it would.
> 
> > If you think that adding that API and maintaining it is
> > simpler/better than including a variation on the above hueristic I
> > offered, then yeah, I guess we are. It'll all have that vague
> > userspace s2ram odor about it, but I'm sure it could be made to work.
> 
> Actually, I overdesigned the API, I suspect.  What we _could_ do is to
> provide a way of allowing userspace to say "pretend process A touched page
> B": adopt its mm and go touch the page.  We in fact already have that:
> PTRACE_PEEKTEXT.
> 
> So I suspect this could all be done by polling maps2 and using PEEKTEXT. 
> The tricky part would be working out when to poll, and when to reestablish.
> 
> A neater implementation than PEEKTEXT would be to make the maps2 files
> writeable(!) so as a party trick you could tar 'em up and then, when you
> want to reestablish firefox's previous working set, do a untar in
> /proc/$(pidof firefox)/

Sick. But thankfully, unnecessary. The pagemaps give you more than
just a present bit, which is all we care about here. We simply need to
record which pages are mapped, then reference them all back to life..

-- 
Mathematics is the supreme nostalgia of our time.
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