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

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Date:	Wed, 25 Jul 2007 23:50:37 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Ray Lee" <ray-lk@...rabbit.org>
Cc:	"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, 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)/

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